New Zealand Veterinary Journal 2003 (in press)
Responsiveness, behavioural arousal and awareness in fetal and newborn lambs:
experimental, practical and therapeutic implications
DJ Mellor*§ and NG Gregory†
*Animal
†
§
Welfare Science and Bioethics Centre, IFNHH, Massey University, Palmerston North, New Zealand.
South Australian Research and Development Institute, Flaxley, SA 5153, Australia.
Author for correspondence. Email: D.J.Mellor@massey.ac.nz
Abstract
This review distinguishes between physical responsiveness, behavioural arousal and awareness in fetal and newborn
lambs, and it summarises the physical and physiological factors which activate and suppress behavioural arousal.
Important activators include rising blood oestrogen concentrations just before birth, physical stimuli during delivery,
exposure to cold on delivery, and elevation in blood oxygen levels following the onset of pulmonary respiration.
Suppressors of behavioural arousal and awareness are low oxygen levels and high concentrations of progesterone
and its metabolites in the fetal circulation, exposure to a warm intrauterine environment and to a circulating placental
factor that inhibits activity including breathing. In view of the levels of oxygen required to sustain awareness in
adult animals, the low levels in the fetal circulation, and the actions of the other suppressors, it is not likely that
awareness occurs in the fetus. Nevertheless, fetuses perform a range of physical acts that would be supported or
initiated by brainstem activity. In addition they show physical responses to potentially painful stimuli during late
gestation, but it has yet to be demonstrated that these are linked to perception of pain. It is postulated that perception
of pain could only occur once there is a level of oxygenation that supports overall awareness, and under normal
circumstances this would only occur once the newborn starts breathing air. The implications for the welfare of the
fetal lambs and calves during experimental surgery, slaughter of the pregnant dam, collection of blood (serum) from
fetuses at slaughter, and fetotomy are favourable, indicating that current practices, when carefully undertaken, are
humane.
Key words: animal welfare, behaviour, arousal, awareness, pain, fetus, birth changes, newborn, fetal surgery,
slaughter, fetal blood (serum) collection, fetotomy.
Abbreviations: ECoG, electrocorticogram; EEG, electroencephalogram; EOG, electro-oculogram; GABAA, aminobutyric acidA; PaCO2, arterial carbon dioxide partial pressure; PaO2, arterial oxygen partial pressure; REM,
rapid eye movement.
Key Points

Responsiveness, behavioural arousal and awareness may be identified by reference to uncoordinated or
coordinated skeletal muscle movements and to ECoG, EOG and breathing activity.
1

The fetal lamb responds to physical stimulation from early in pregnancy, behavioural arousal becomes evident
during late pregnancy, and awareness may appear for the first time only after birth.

Suppressors of behavioural arousal and awareness operate before birth and activators of them operate during
and immediately after birth.

Although the fetal lamb is not likely to be arousable to an aware state by noxious stimulation in utero, as a
precaution fetal surgery should only be conducted when both the mother and fetus are under general anaesthetic.

Slaughter of pregnant ewes stops placental O2 supply within seconds and, within 1 to 2 min at most, induces
very severe fetal hypoxaemia and a flattening of the fetal ECoG. Such fetuses are not capable of behavioural
arousal or awareness. Fetal lambs are therefore not likely to suffer during slaughter of their dams, and nor are
fetal calves.

Provided that fetal calf blood (serum) collection does not begin until cerebral hypoxia/anoxia has flattened the
fetal ECoG and provided the calf is prevented from breathing air, blood (serum) collection will be humane.
Allowing a safety margin, collection could begin 5 to 6 min after slaughter of the dam, but is normally delayed
for at least 20 min in Australia and New Zealand.

If the umbilical cord can be reached, it should be severed manually 5 to 6 min before fetotomy, if not, other
precautions need to be taken to maximise the humaneness of fetotomy.
Introduction
At the moment of birth the newborn lamb has no prior experience of extrauterine life. All situations it encounters
immediately afterwards are new and the intensity and character of the associated sensory inputs are obviously
transformed markedly by the event of birth. For instance, the fetus is buoyant in amniotic fluid, cushioned by soft
maternal tissues and fluids, cramped within a restricted space and its body temperature is kept just above that of the
mother (Mellor 1969, 1980, 1984; Gluckman et al 1984; Fraser and Broom 1990), whereas after birth the newborn is
exposed to gravity, air, hard surfaces, unlimited space and, usually, to cold challenge for the first time (Fraser and
Broom 1990; Lynch et al 1992). To survive, the newborn lamb must, among other things, immediately start to
breathe effectively (Mott 1961; Dawes et al 1972a) and, in cold conditions, it must also increase its heat production
(Eales and Small 1980). From about 20 to 60 minutes after birth viable lambs of different breeds will stand, and
then walk, locate the mother and her udder, drink colostrum and, in cold conditions, seek shelter (Mellor and Pearson
1977; Slee and Springbett 1986; Lynch et al 1992). Such behaviour is possible because, by the time of birth, the
sensory apparatus of the lamb, along with numerous other neurological structures, have developed sufficiently for the
lamb to use sight, hearing, smell, taste, touch, proprioception and thermal sensitivity effectively (Fraser and Broom
1990; Lynch et al 1992). Such behaviour presumably reflects the operation of innate drives initially, but learned
reactions become evident subsequently (Fraser and Broom 1990; Lynch et al 1992). This suggests that the lamb may
become more aware of its actions and surroundings as time passes, but it is not clear to what extent the lamb is aware
immediately after birth, or indeed before birth.
The lamb has been and continues to be used widely for biomedical and veterinary studies of fetal and neonatal
physiology and pathophysiology (e.g. Meschia et al 1965; Mellor and Slater 1971; Liggins et al 1973; Mellor 1987;
Harding et al 1981; Clewlow et al 1983; Berger et al 1990; Clapp et al 1988; Gluckman et al 1989; Richardson et al
1996; Johnston et al 1998; King and McCullagh 2001). This has greatly advanced knowledge of ovine prenatal
2
development and the practical or therapeutic application of that knowledge to enhancing the survival, health and
well-being of the newborn lamb (Alexander 1980; Mellor 1983, 1988; Eales and Small 1995) and, by careful
extrapolation, of other animals including the newborn human infant (e.g. Mellor and Cockburn 1986; de Haan et al
1996; Gunn et al 1998). Recent attention given to awareness in postnatal animals (e.g. Lehman 1998; Piggins and
Phillips 1998; Sommerville and Broom 1998; Kirkwood et al 2001) raises the question of the extent to which our
current knowledge of prenatal development and responsiveness permits conclusions to be drawn about awareness in
the fetus and newborn. Accordingly, the behavioural and physiological bases of the potential for arousal and
awareness in fetal and newborn lambs are considered in the early part of the present review.
These matters are directly relevant to the welfare of fetal and newborn lambs. During surgical preparation of the fetal
lamb for physiological and pathophysiological studies it is exposed to potentially noxious stimulation so that the
extent to which it might be aware in utero is relevant to whether procedures should be conducted using epidural,
paravertebral or general anaesthesia of the ewe. In addition, significant numbers of pregnant ewes, and other
ruminants (Ladds et al 1975), are slaughtered annually and their fetuses die in utero from hypoxia and hypercapnia
or, in some cases, from exsanguination during fetal blood (serum) collection. This raises the question of whether or
not such fetuses might suffer before they die. Finally, the capacity of the fetus to be aware during birth has direct
bearing on the humane management of fetotomy on those occasions when living fetuses need to be dismembered in
utero in order to resolve intractable dystocia. The later part of present review therefore addresses the welfare
implications of these practices for lambs and, where appropriate, for calves.
Awareness
Awareness is linked to wakefulness and, in general, implies that responses to stimuli involve higher brain centres and
are not merely reflexes (Sommerville and Broom, 1998).
Unaware but physically responsive
In this situation, afferent and efferent neural pathways have developed but, following some sensory input which
elicits a movement for example, complex cortical processing does not take place (Sommerville and Broom, 1998).
In the fetal lamb at different gestational ages it is thought that physical movements might occur without cortical
processing when impulse traffic does not ascend the spinal cord, or the required neural connections to the brain are
not yet in place, or its higher neural structures are poorly developed. In the present review the word responsiveness
means physical responsiveness, and when used without qualification relates only to unawareness.
Perceptual awareness
With awareness of this type, a perceived stimulus involves higher brain centres and causes a response which the
individual may or may not be able to modify voluntarily (Sommerville and Broom, 1998).
Non-modifiable
responses in perceptually aware young lambs may include spinal reflex responses to pain, and blinking when an
object passes close to the eye. Modifiable responses in such lambs may include scratching to relieve irritation.
3
Fetal and neonatal behavioural arousal and awareness
Fetal movements and what they mean
Fetal movements begin early in pregnancy (Barcroft and Barron 1937, 1939; Fraser 1989; Fraser and Broom 1990;
Berger et al 1997). Initially they are uncoordinated and involve local movements of the limbs, trunk or neck. As the
fetus matures the movements become stronger and more coordinated (some of which appear to be directed towards
changing the body’s orientation within the amniotic sac) and exhibit alternating periods of activity and inactivity
(Ruckebusch et al 1977: Rigatto et al 1982; Clewlow et al 1983; Fraser 1989; Fraser and Broom 1990; Berger et al
1997).
These changes reflect the way that neural and neuromuscular development progresses from sparsely
connected rudimentary precursors of nerve tracts and brain structures very early in pregnancy to the well-defined,
complex, sophisticated and operationally effective, yet still maturing, structures that are present at birth (Barlow
1969; Bernhard and Meyerson 1973; Persson 1973; Cook et al 1987; Nitsos and Rees 1993; Nitsos et al 1994; Rees
et al 1994a, b; Fitzgerald 1996; Berger et al 1997). Apart from body stretching and other limb, trunk and neck
movements, totalling about 4,000 to 6,000 movements per day during the last 14 days of pregnancy, the fetal lamb
also exhibits gasps, sighs and shallow breathing, jaw, swallowing and tongue movements, eye movements and eyelid
opening and closing. Of particular interest here, however, is what fetal movements – fetal behaviour – might suggest
about the developmental interplay between physical responsiveness, behavioural arousal and awareness before birth
and about the manifestation of behavioural arousal and awareness after birth. Some of the behaviours that are
observed in the fetal lamb are undoubtedly rudimentary and can occur below the level of normal awareness. This is
evident from comparable behaviours that occur in human subjects who are in a vegetative state intellectually. For
example, the severely hydranencephalic infant has been observed to grimace in response to potentially painful
stimuli, to keep its eyes open, swallow and breathe spontaneously (Pallis 1982). These are brainstem functions
which do not signify higher levels of consciousness, but some of them demonstrate that the subject is not comatose.
Fetal sleep states
Distinct EEG, ECoG and EOG patterns are present in adult animals during wakefulness (awareness) and sleep
(Empson 1993; Akerstedt et al 1998; Endo et al 1998; Baars 2001; Landolt et al 2001). The same patterns of slowwave, synchronised EEG activity observed during deep sleep, which is an arousable form of unconsciousness, are
also evident in other states of global unconsciousness including general anaesthesia and coma (Baars 2001). States
resembling slow-wave and REM sleep become established in fetal lambs at 110 to 125 days in the 147-day
pregnancy in sheep (Dawes et al 1972b; Harding et al 1981; Clewlow et al 1983; Berger et al 1986; Dawes 1988),
such that near birth the fetal lamb spends most of its time (all but about 5 minutes in every hour) in those states.
Fetal behavioural arousal
Behavioural arousal is distinguished from sleep in fetal lambs by low-voltage ECoG activity, together with increases
in eye movements (EOG), postural muscle activity, breathing and responsiveness to somatic stimulation (Harding et
al 1981; Rigatto et al 1982; Clewlow et al 1983). Thus, such arousal, defined physiologically and behaviourally, can
be demonstrated and is distinct from fetal sleep states.
4
During labour the character of the fetal lamb’s ECoG changes, such that the time spent in low-voltage as opposed to
high-voltage states declines significantly and a mixed high/low-voltage state appears for the first time (Berger et al
1986). Moreover, fetal motor systems in general, including the respiratory system, are largely quiescent during
labour (Berger et al 1986; Fraser and Broom 1990; Hasan and Rigaux 1991), so that fetal behavioural arousal
apparently does not increase markedly during labour.
Newborn behavioural arousal and perceptual awareness
Immediately after birth a viable lamb lies immobile on the ground. Soon it shakes its head and gasps several times
before regular breathing begins. Within very few minutes it makes minor movements of the head, neck and limbs,
movements which increase in intensity and co-ordination as the lamb first holds its head up and then tries to stand.
Thus, behavioural arousal is usually evident in the newborn lamb within a few minutes of birth and accompanies the
onset of pulmonary respiration (Mellor et al 1972; Mellor and Pearson 1977; Berger et al 1990; Lynch et al 1992).
Although perceptual awareness is evident by 20 to 60 minutes after birth when the lamb stands for the first time and
starts teat seeking (Mellor and Pearson 1977; Slee and Springbett 1986; Fraser and Broom 1990), it is not clear
whether or not the lamb at birth immediately becomes aware of its surroundings and, if it does not, when such
awareness appears.
After birth, behavioural arousal might appear before awareness, arousal and awareness might appear simultaneously,
or awareness might appear before arousal. Whatever the case, both are required for survival of the newborn lamb.
Without behavioural arousal and the associated onset of pulmonary respiration the lamb will die of
hypoxaemia/hypercapnia very soon after birth. Without perceptual awareness the lamb will not be able to interact
with its mother, a strong ewe-lamb bond will not be established and the lamb will not receive colostrum and will die
later from starvation.
It is still not clear whether the short periods of fetal behavioural arousal during late pregnancy simply reflect
enhanced yet unconscious reflex responsiveness or indicate the earliest stage when short periods of fetal awareness
might be possible. It is clear, however, that lambs rapidly show signs of behavioural arousal and perceptual
awareness after birth, and that these bouts of arousal last longer than those in utero. This raises the question of
whether birth removes suppressors of behavioural arousal and/or in some way triggers or activates it (Table 1).
Suppressors and activators of fetal and neonatal behavioural arousal and awareness
Fetal oxygen and carbon dioxide status
Suppression
The fetal lamb’s PaO2 is usually less than about 25 per cent and its PaCO2 is usually more than about 135 per cent of
the respective values in the conscious ewe (Jones 1977; Jones et al 1977; Robinson et al 1979; Jensen et al 1991).
The low PaO2 and high PaCO2 in the fetus exist because of the concentration gradients required for these gases to
diffuse across the placenta (Meschia et al 1965; Comline and Silver 1970; Silver et al 1973). In mature animals
including human beings, severe hypoxaemia (PaO2 below about 28 mm Hg) causes unconsciousness (Brierly et al
1980; West et al 1984; Hattingh et al 1986). As carotid arterial O 2 tensions are usually 20 to 27 mm Hg in normal
5
and 12 to 18 mm Hg in placentally deficient fetal lambs (Jones, 1977; Jones et al 1977; Robinson et al 1979, 1983;
Harding et al 1985; Jensen et al 1991), the fetal brain is usually exposed to O 2 tensions that would cause
unconsciousness during postnatal life. This suggests that fetal arousal and awareness may be suppressed by the low
O2 status. This proposition is strongly supported by the observation that higher than normal fetal O 2 tensions in the
presence of normal CO2 tensions apparently stimulate continuous breathing and behavioural arousal in fetal lambs
(Baier et al 1990; Hasan and Rigaux 1991). Also, acute reductions in fetal PaO 2 decrease the incidence of
behavioural arousal (Bocking and Harding, 1986). However, during chronic moderate hypoxaemia, an initially
reduced incidence of fetal behavioural arousal returns to normal levels within about 16 hours (Bocking et al 1988).
This recovery presumably results from circulatory adjustments during hypoxaemia that enhance blood flow to the
fetal brain (Rudolph et al 1981; Rudolph, 1984), supported by the higher haematocrit in the fetus than in the mother
(Meschia et al 1965) and the greater capacity of fetal haemoglobin to deliver O 2 to fetal tissues (including the brain)
at lower than adult O2 tensions (Meschia et al 1961). In contrast, severe chronic hypoxaemia sufficient to cause a
metabolic acidosis markedly reduces the signs of behavioural arousal (Richardson et al 1992), as do repeated short
periods of severe hypoxaemia caused by reversible umbilical cord occlusion in utero (Gunn et al 1992).
Several observations in newborn lambs and calves are also relevant. First, hypotension and hypoxia are potent
stimuli that arouse normoxaemic lambs from sleep (Horne et al 1989; Johnston et al 1998), but they are less effective
in arousing lambs exposed to continuous or repeated short bouts of moderate hypoxaemia (Fewell and Konduri
1988, 1989; Walker et al 1993; Johnston et al 1998). Note that the PaO 2 during hypoxaemia in these postnatal lambs
(PaO2, 40-60 mm Hg) was greater than that in normoxaemic fetuses (20 to 27 mm Hg). Second, active, perceptually
aware newborn lambs, immersed in water at maternal body temperature and exposed to 2.5 to 7.5 per cent O 2 in
inspired air for a sufficient period to elicit a metabolic acidosis equivalent to that caused by severe hypoxaemia
during birth, rapidly exhibit depressed behavioural arousal, awareness and respiratory activity (a state distinct from
sleep), but return to an aware, active state when given room air to breathe (Eales and Small 1985). Third, the
behaviour of newborn calves which breathed air (21% O 2) for the first 2-3 minutes after birth and then breathed a gas
mixture (10.5% O2) designed to maintain their arterial O2 tensions at about 25 mm Hg for 24 hours (Tyler and
Ramsey, 1991; HD Tyler, unpublished observations), is of interest. Apparently the calves were initially fairly active,
but quickly became lethargic and then increasingly sleepy and unresponsive as the period of hypoxaemia progressed
(HD Tyler, unpublished observations).
The weight of evidence therefore suggests that the incidence of fetal behavioural arousal is a function of the arterial
O2 tension, with greater than normal O2 tensions increasing it and lower than normal O2 tensions decreasing it,
sometimes transiently. Thus, it appears that during fetal normoxaemia, the PaO 2 does have a suppressive effect on
behavioural arousal in fetal lambs, but does not abolish it.
In contrast, the somewhat elevated fetal blood CO2 tensions (40 to 50 mm Hg) may not be sufficiently high to
suppress arousal and awareness because the arterial CO2 tensions required to induce anaesthesia in adult dogs (220
mm Hg; Eisele et al 1967) and monkeys (at least 115 mm Hg; Mattsson et al 1972), and comatose or semi-comatose
states in human beings (130 mm Hg; Sieker and Hickam 1956), are much higher. Nevertheless the combination of
low O2 and high CO2 tensions may synergistically enhance the suppressive effects of each gas alone (Mohan Raj et al
1992).
6
Activation
Although low blood O2 and/or high blood CO2 tensions in the fetal lamb apparently inhibit breathing in utero, as
already noted higher than usual fetal O2 tensions in the presence of normal CO2 tensions apparently stimulate
continuous fetal breathing and behavioural arousal (Baier et al 1990; Hasan and Rigaux 1991), especially after about
135 days of gestation (Hasan and Rigaux 1991). This suggests that the marked increases in O 2 and decreases in CO2
tensions that accompany the onset of pulmonary respiration immediately after birth (Comline and Silver 1972;
Mellor and Pearson 1977; Berger et al 1990) both remove an inhibition to continuous breathing and arousal (due to
low O2 and high CO2), and actively stimulate continuous breathing and arousal (due to high O 2). The onset of
breathing also rapidly increases the lamb’s PaO2 to levels well above the 28 mm Hg threshold for awareness in
mature postnatal animals (Brierly et al 1980; West et al 1984; Hattingh et al 1986) and may thereby play a major role
in promoting awareness in the lamb shortly after birth.
Clearly the onset of breathing is critical for these changes to occur. Breathing is apparently initiated in the newborn
lamb by the combined effects of several factors including umbilical cord occlusion (Adamson et al 1987; 1991) and
low blood O2 and high blood CO2 tensions (Boddy et al 1974; Jansen et al 1982; Rigatto et al 1988) immediately
after birth.
Fetal progesterone and oestrogen status
Suppression - progesterone
Progesterone, its metabolites and/or synthetic analogues have potent sedative and anaesthetic actions in adult
animals, including human beings (Paul and Purdy 1992). Progesterone metabolites can interact with GABA A
receptors, enhancing GABA binding to them, thereby increasing the activity of GABA inhibitory pathways in the
central nervous system (see Crossley et al 1997).
In the pregnant ewe the placenta produces large quantities of progesterone throughout at least the last half of
pregnancy, especially during the last 20 to 30 days (Bassett et al 1969), and thus exposes the fetus to high circulating
concentrations of progesterone and its metabolites (Seamark et al 1970; Dolling and Seamark 1979). In fetal sheep
GABAA receptors are apparently present in the brain from at least 56 days of gestation and reach adult levels by 120
days, about 27 days before birth (Villiger et al 1982). During the last 20 to 30 days of pregnancy, injections of
progesterone or its metabolites into the fetal circulation or cerebral ventricles reduce fetal EEG, ECoG and EOG
activity, breathing movements and behavioural arousal, and inhibition of placental progesterone production enhances
them (Crenshaw et al, 1966; Crossley et al 1997: Nicol et al 1997, 1998; Hirst et al 2000). This strongly implicates
progesterone and its metabolites as suppressors of fetal behavioural arousal.
During the last 3 to 5 days before birth in sheep placental progesterone production declines as placental
steroidogenesis increasingly favours oestrogen production under the action of the marked surge in fetal cortisol
production that precedes birth (Liggins et al 1973; Thorburn and Challis 1979). An associated prenatal decline in
progesterone (Power et al 1982) and its metabolite levels within the fetal circulation would reduce the associated
suppressive effects on behavioural arousal in the near-term fetal lamb and would presumably facilitate the
appearance of arousal in the lamb after birth.
Activation - oestrogen
7
Several observations suggest that fetal oestrogen status can affect behavioural arousal. First, inactive fetal lambs
delivered under epidural anaesthesia of the ewe during mid-pregnancy “quickly” become active when injected with
oestradiol-17 (DH Barron, unpublished observation). Second, inactive lambs, delivered prematurely very close to
the time of normal birth, start breathing and become aroused behaviourally within 30 to 60 seconds of being injected
with oestradiol-17 (Mellor et al 1972). Third, the switch in placental steroidogenesis away from progesterone
which occurs just before birth (Liggins et al 1973; Thorburn and Challis 1979), leads to increasing secretion of
oestrogens into fetal plasma (Challis and Patrick 1981) and, thus, exposes fetal neural tissue to rising concentrations
of oestrogens.
Although the mechanism by which oestrogens stimulate behavioural arousal and continuous
respiration is not known, the preparturient surge in its circulating concentrations (Challis and Patrick 1981) has the
clear potential to actively prepare the lamb to become behaviourally aroused and start breathing immediately after
birth.
Fetal thermal status
Suppression - warmth
There is evidence that the thermal status of the fetal lamb – in particular warmth – suppresses behavioural arousal.
First, the fetus is slightly hyperthermic in relation to the mother because the heat it generates can only be dissipated
down a thermal gradient across the placenta (Gluckman et al 1993). Second, mature fetal lambs cooled in utero such
that their cutaneous thermoreceptors are exposed to cold (via cooling coils in amniotic fluid), exhibit behavioural
arousal, shivering and increased respiratory activity, and rewarming such fetuses reverses these effects (Gunn et al
1985, 1986, 1991; Gluckman et al 1993). Third, aroused, physically active and perceptually aware newborn lambs
immersed in water at maternal body temperature assume a sleep-like, non-aroused, unaware state, and cooling the
water restores their prior aroused, aware and physically active state (Eales and Small 1980).
Activation - cold
At birth the newborn lamb commonly, but not invariably, enters air temperatures significantly below maternal body
temperature.
This would immediately remove the suppressive effect of prior warmth on behavioural arousal.
Indeed, the above evidence suggests that cold-activation of cutaneous thermoreceptors is a strong stimulus for
behavioural arousal after birth (Eales and Small 1980; Gunn et al 1985, 1986, 1991; Gluckman et al 1993).
Fetal tactile stimulation
Suppression and activation
Amniotic fluid buffers the embryo/fetus against mechanical stimulation and presumably also reduces sensations
associated with gravity, and thereby minimises tactile sensory input likely to stimulate behavioural arousal. Thus,
transfer from complete immersion in amniotic fluid in utero into the postnatal air environment leading to marked
increases in such sensory effects, may contribute to the usually rapid onset of arousal in the newborn. In addition,
manual stimulation of the ears, nose and other areas of the head of inactive newborn lambs often elicits strong
kicking and appears to aid the subsequent onset of continuous pulmonary respiration (DJ Mellor, unpublished
observations). This suggests that the compression of these body parts by the cervix and vagina during birth, and by
licking from the ewe shortly after birth, may actively help to initiate the behavioural arousal and breathing usually
seen in the lamb straight after birth.
8
Placental inhibitor
Suppression
Occluding the umbilical cord (reversibly) in the presence of adequate oxygenation via a tracheal catheter induces
behavioural arousal and continuous breathing in experimentally studied fetal lambs (Alvaro et al 1993). Infusion of
a placental extract, or a sub-fraction of it, but not the vehicle, abolished this fetal arousal and respiration within two
minutes. This suggests that a placental factor, probably a peptide, inhibits arousal and breathing during fetal life
(Alvaro et al 1993). Clearly, loss of the placenta at birth would cause an immediate decrease in the circulating
concentrations of this factor, thereby removing its inhibitory effects on behavioural arousal and respiration.
Behavioural arousal and awareness in the fetal and newborn lamb – an integrated
hypothesis
The weight of evidence presented above suggests that although fetal lambs subjected to usual in utero sensory inputs
exhibit brief periods of behavioural arousal during at least the last 20 to 30 days of pregnancy, perceptual awareness
appears for the first time only after birth. The reasons for this are suggested to be as follows. A major factor is the
fetal and neonatal O2 status. Normal fetal arterial O2 tensions (PaO2, 20-27 mm Hg) would cause unconsciousness
postnatally in mature lambs and adult sheep, moderate hypoxaemia (PaO 2, 40-60 mm Hg) inhibits arousal from sleep
in very young lambs, normal fetal O2 tensions are associated with relatively low levels of behavioural arousal (about
5 minutes in every hour) in fetal lambs, and higher than normal fetal O 2 tensions increase the incidence of fetal
behavioural arousal. Moreover, progesterone and its metabolites, buoyancy, cushioned tactile stimulation, warmth
and a placental inhibitor apparently also act to suppress fetal behavioural arousal (Table 1). However, the removal
or reversal of their effects before, during and immediately after birth (Table 1), together with an acute worsening of
fetal hypoxaemia/hypercapnia (Comline and Silver 1972; Mellor and Pearson 1977; Berger et al 1990) and umbilical
cord occlusion (Adamson et al 1987; 1991), are suggested to have the primary function of arousing the newborn
lamb sufficiently for it to initiate pulmonary respiration immediately after birth. Although the newborn is aroused at
this stage, it is not yet likely to be aware. It is postulated that only after the lamb has begun to breathe effectively and
its arterial O2 tensions have risen significantly above fetal levels would it display the first signs of perceptual
awareness. If true, the absence of awareness until after birth would indicate that the fetal lamb exposed to usual in
utero sensory inputs cannot suffer during pregnancy or during birth, and that animal welfare compromise (suffering)
can only be experienced postnatally once the lamb has become perceptually aware.
Implications for fetal lambs during surgery
Surgical procedures with the fetal lamb and ewe under general anaesthetic have usually been conducted between
about 80 and 135 days of the 147-day pregnancy (e.g. Mellor 1980, 1984; Harding et al 1981; Clewlow et al 1983;
Berger et al 1986; Richardson et al 1996; Nichol et al 1998; King and McCullagh 2001), with some done as early as
40 days of gestation (e.g. Berger et al 1997). Such surgery has involved catheterisation, instrumentation and/or
tissue ablations of fetal lambs to allow them to be studied in conscious, unstressed ewes once the effects of the
anaesthesia and surgery have passed. Small body size and tissue fragility are major limitations to studying very
9
young fetuses, and difficulty in manipulating large fetuses and a greater chance that surgery will induce premature
birth when conducted after about 135 days of gestation usually set the upper age limit.
Experienced fetal surgeons report that such invasive procedures do not cause withdrawal or other movements by
fetal lambs from about 60 days of gestation or later provided that the general anaesthetics given to the ewe have had
sufficient time to act on the fetus (PJ Berger, JE Harding, R Harding, DJ Mellor, AM Walker, DW Walker and IR
Young, independent unpublished observations). In contrast, surgery on unanaesthetised fetuses in ewes given
epidural anaesthesia, an approach used rarely during the last 30 years, elicits strong leg, trunk and/or neck
movements, especially after about 120 days of gestation. These observations show that general anaesthesia of the
ewe is effective in virtually eliminating behavioural responses of the fetus to surgical stimulation. Such behavioural
responses to noxious stimuli in newborn and young lambs are considered to indicate the generation and awareness of
pain (Mellor and Murray 1989; Kent et al 1998), but the situation in the fetus is not as clear.
The fetal responses to putatively painful stimuli appear to be somewhat exaggerated, and a simple interpretation is
that the fetal lamb is more sensitive to painful stimuli. However, this may not be the case. Instead, based on findings
in rat pups, it is just as likely that the strong behavioural responses in the fetus occur because they have not yet been
entrained under central inhibitory control (Fitzgerald, 1999). Thus, the exaggerated responses are probably a feature
of immaturity of the central nervous system rather than enhanced pain perception. The capacity to feel pain can be
inferred by the presence and activation of appropriate functional nerve pathways in combination with behavioural
effects. Unfortunately knowledge in that area does not extend to quantitative assessment of pain, but the inference is
that as the newborn lamb is capable of responding to undoubtedly painful stimuli (Mellor and Murray 1989), the
mature fetal lamb would have the capacity for neurotransmission in pain pathways. This raises the question of
whether or not the increased behavioural activity of unanaesthetised fetuses due to surgical stimulation indicates
responsiveness without arousal, arousal or both arousal and awareness. In part, this will depend on the age of the
fetus and its associated neurological development. If noxious surgical stimulation, which is not usually encountered
in utero, were to induce a state of awareness, the fetus would presumably feel pain.
It seems likely that fetal surgery applied to the hind- and fore-quarters, but not to the head, of the unanaesthetised
fetal lamb before about 105 days, and possibly as late as about 120 days of gestation, may simply induce
responsiveness without arousal.
After about 120 days, however, arousal might be elicited.
The reasons for
proposing this are as follows. First, stimulation by light touch or stretch of hind limb receptors in fetal lambs elicits
electrical discharges in dorsal root ganglia and/or dorsal horn cells of the spinal cord from about 75 days of gestation
(Rees et al 1994a, b), and fibres projecting from dorsal horn cells, and presumably entering the spinothalamic tract,
can carry signals at least as far as the thoracic spinal cord from about 105 days (Rees et al 1994a). Second, although
it is not known at what fetal age sensory signals from the hind limb might reach the cerebral cortex (Rees et al
1994a), electrical activity in the somatosensory cortex can be elicited by sensory input from the forelimb from about
125 day of gestation (Cook et al 1987). Third, behavioural arousal in chronically instrumented, non-stimulated fetal
lambs, well after recovery from the associated surgery, becomes evident only from about 120 days of gestation
(Ruckebusch et al 1977; Clewlow et al 1987).
In contrast to surgical stimulation of the body, stimulation of the face of unanaesthetised fetal lambs has the
potential to elicit behavioural arousal earlier than 120 days of gestation, as electrical activity can be evoked in the
somatosensory cortex by input from the nose and lips of the fetal lamb from about 70 days (exteriorised fetus;
10
Persson 1973) or 97 days (chronically instrumented fetus; Cook et al 1987). However, this could occur only if
neurophysiological development within the brain prior to about 120 days were such that the noxious stimulation of
surgery, not usually encountered in utero, could override any inhibition to behavioural arousal which might exist
before it appears naturally in the non-stimulated fetus.
Even if mature, unanaesthetised fetuses were to become both responsive and behaviourally aroused during surgery, it
is not likely that they would become aware. Direct fetal surgery usually involves partial exposure of the uterus
through an abdominal incision (with the mother anaesthetised), removal of some portion of the fetal fluids (returned
later) and partial or complete exposure of the fetus through an incision in the uterine wall. Such exposure and
manipulation of the uterus and fetus usually compromises uterine and/or umbilical blood flow and placental gas
exchange and leads to increased fetal hypoxaemia and hypercapnia (Barcroft et al 1940; Barron and Meschia 1954;
Meschia et al 1965; Comline and Silver 1970, 1972). This fetal hypoxaemia/hypercapnia becomes progressively
worse the nearer to birth the uterine and fetal exposure occurs (Barcroft et al 1940; Barron and Meschia 1957), so
any associated suppressive effects on fetal arousal and awareness (Table 1) would thereby be increased in older,
more mature and otherwise potentially more arousable fetuses. It is also noteworthy that the bovine placenta and
amniotic fluid contain a substance which promotes analgesia (Pinheiro Machado et al 1997). Its effect depends on a
simultaneous elevation of opioid levels, and the substance, known as placental opioid enhancing factor, has not yet
been characterised. Its actions have been examined in the mother, but not in the fetus and newborn where they may
be more relevant.
Notwithstanding this analysis, it is recommended that, in accord with common practice during the last 30 years,
general anaesthesia of the mother and fetus be used both to minimise fetal movements (responsiveness) during
surgery and to make sure that the fetus remains unaroused and unaware throughout. Note, however, that even while
it is completely anaesthetised the fetus will exhibit physiological stress responses due to direct surgical stimulation,
to cooling and to increased hypoxaemia/hypercapnia through compromised placental gas exchange (Jones 1977;
Jones et al 1977; Gunn et al 1985, 1986). Such stress responses also occur in adult ewes during surgery conducted
under general anaesthesia (Pearson and Mellor 1975) and do not indicate awareness.
Implications for fetuses during slaughter of pregnant ewes
Sheep are usually slaughtered by a neck cut that severs both carotid arteries and jugular veins. Although most
commercial slaughter is preceded by electrical or captive-bolt stunning, most non-stunned sheep apparently
experience profound brain dysfunction within 5 to 7 seconds (maximum 22 seconds) through a catastrophic decline
in blood flow to the brain during exsanguination (Newhook and Blackmore 1982; Gregory and Wotton 1984). Fifty
per cent of the blood that is voided following the neck cut is lost during the first 10 seconds, and this corresponds to
about one third of total blood volume (Gregory and Wilkins 1984). Systemic blood pressure at this stage is
substantially reduced. Indeed it is too low to allow the development of a bruise. This implies that peripheral
resistance exceeds systemic pressure from about 10 seconds after the neck cut, and it is anticipated that blood flow in
the uterus would cease near to this time. In pregnant ewes placental gas exchange would also stop and this would
rapidly lead to very severe fetal hypoxaemia and hypercapnia and to a sudden marked reduction in O 2 delivery to the
fetal brain (Jensen et al 1987). This is likely to cause a rapid flattening of the fetal ECoG and quickly eliminate any
potential for behavioural arousal or awareness, because ECoG activity of fetal lambs is substantially depressed
11
within 1 minute of complete umbilical cord occlusion in utero (Mallard et al 1992) and becomes isoelectric when
pregnant ewes breathe a gas mixture containing no O2 for about 5 minutes (Mann et al 1970).
However, the rapid worsening of fetal hypoxaemia/hypercapnia after the throat cut of the ewe has the potential,
initially, to stimulate behavioural arousal, especially in fetuses close to birth (Boddy et al 1974; Jansen et al 1982;
Rigatto et al 1988), because the increased hypoxaemia/hypercapnia seen during normal vaginal birth and subsequent
severance of the umbilical cord apparently does so (Berger et al 1990). Indeed, some near-birth fetal lambs
delivered by hysterectomy, using epidural anaesthesia of the ewe, have been seen to lift their heads within 10 to 30
seconds while still inside the excised uterus (DJ Mellor, unpublished observations relating to Hart et al 1971).
Although these fetal lambs were delivered immediately and successfully revived (the purpose was to produce live
lambs), had they been left in the uterus their PaO2 would have continued to fall rapidly to levels incompatible with
either behavioural arousal or awareness, because in fetal lambs in utero the PaO 2 falls to about 30 per cent of fetal
normoxaemic levels within two minutes of complete umbilical cord occlusion (Mallard et al 1992). Thus, although
some near-birth fetal lambs may initially exhibit behavioural arousal soon after the throat cut in slaughtered pregnant
ewes, this is likely to be short-lived (1 to 2 minutes at most) and probably would not be accompanied by awareness,
because the PaO2 would remain well below the suggested threshold for awareness (Brierly et al 1980; West et al
1984; Hattingh et al 1986).
As the key features of the physiology of fetal lambs, calves and other ruminants are likely to be similar in these
respects, slaughter of pregnant ruminants, whether near to birth or not, is not likely to cause their fetuses any
suffering prior to death in utero.
Implications for collection of fetal calf blood (serum) and other tissues at slaughter
Collection of fetal calf blood (serum) occurs in some processing plants after the pregnant uterus has been removed
from the cow at the evisceration stage, which usually occurs no sooner than 20 to 30 minutes after the neck cut in
Australia and New Zealand. This, plus veterinary inspection, means that blood (serum) collection usually does not
begin earlier than 25-40 minutes after slaughter of the cow. Two main collection methods, or variations of them, are
used. After partial or complete removal of the calf from the uterus, either (i) a 12 to 16 gauge needle attached to a
tube is inserted between the 4th and 5th ribs into the fetal heart and blood is collected into bottles under vacuum until
no more flows, or (ii) the fetus, suspended from an A-frame, has a device which simulates a pumping action placed
over the thorax and blood is collected from the unclamped umbilical cord until flow stops. The usual practice of
collecting blood (serum) at least 20 minutes after slaughter of the cow ensures that the fetuses experience prolonged
cerebral anoxia, would be unaware and therefore could not suffer during the process.
Manipulating calf or lamb fetuses from 5 to 6 minutes after slaughter of the dam is usually not undertaken in
commercial processing plants in Australia and New Zealand, but may occur in some plants elsewhere (Jochems et al
2002). However, this could be done humanely provided that particular precautions are taken. The observations on
sheep slaughter noted above, and the observation on a small number of cows that 6 to 8 minutes of umbilical cord
occlusion in utero is sufficient to cause subsequent death in fetal calves (Dufty and Sloss 1977), indicate that
provided at least 5 to 6 minutes elapse after the neck cut of the dam, the fetus would be severely
hypoxaemic/hypercapnic, would have a flat ECoG and would be unaware when removed from the uterus. However,
12
its heart may still be beating at this early stage and intermittent gasping may occur, so that near-birth fetuses which
are still alive when removed from the uterus soon after slaughter of the dam have the potential to start breathing and
become aware. There are two simple ways to prevent this. The fetus’s head can be retained inside part of the
amniotic sac or the trachea can be clamped so that gasping cannot inflate the lungs, thereby ensuring that the fetus
remains unaware and incapable of suffering. Stunning the fetus with a captive bolt has also been suggested (Jochems
et al 2002).
Collection of other fetal tissues, including the hide, should be done only after the fetus is dead. Processing can be
delayed until then. Alternatively, if the heart is still beating when the fetus is exposed, cutting its throat immediately
would guarantee that it remained unaware before death.
Implications for undertaking fetotomy
It is often difficult to tell whether an undelivered fetus requiring fetotomy is still alive. A straightforward method,
especially for posterior and breach presentations where the umbilical cord is usually accessible, is to feel for a pulse
in the cord. Note however that the presence of a pulse provides little information about fetal O 2 status. Depending
on whether or not the required fetal parts are accessible, withdrawal responses can sometimes be elicited in living
fetuses by strongly pinching the tongue, a lip or the anus or by applying strong pressure to the supraorbital ridge of
an eye socket. Responses to these stimuli are interpreted by some veterinarians as indicating fetal awareness, but if
great pressure is required to achieve a response it is more likely that deep reflexes are being elicited in unaroused
fetuses which have become severely hypoxaemic during the protracted labour that usually precedes the decision to
undertake a fetotomy.
Fetuses that respond to moderate tongue, lip, anal or supraorbital stimulation, or that
withdraw a leg in response to it being pulled or to pedal reflex stimulation, or “chew” or suck on a finger placed in
the mouth, are likely to be less hypoxaemic and are therefore potentially more arousable by noxious stimulation.
Where an undelivered fetus requiring fetotomy is still alive and the umbilical cord can be reached via the vagina, the
cord should be severed manually. Such a fetus would not be arousable to an aware state while still in utero from 2 to
3 minutes after cord severance (Mallard et al 1992), so, allowing a safety margin and also for the attainment of an
isoelectric EEG (Mann et al 1970), fetotomy could be conducted humanely from 5 to 6 minutes after cord severance.
Cord severance may be more easily accomplished with fetal lambs than fetal calves because of the longer reach
required in the latter. If the cord cannot be severed, other strategies should be attempted to ensure that the fetus is
not aware, or to kill it, before fetotomy is conducted. When the head and neck are delivered but the shoulders are
jammed, the fetus can be killed by a throat cut and exsanguination before fetotomy. Where the head is not delivered
- for instance, when the fetus is in a “head-back” position with its neck and/or a shoulder presented to the cervix decapitation using an embryotomy wire, which is achievable within about 30 seconds once the wire is correctly
placed, would kill the fetus. Depending on its O2 status, the initial cutting of the neck required to sever the carotid
and vertebral arteries may elicit fetal behavioural arousal, but, if this occurred, it would be expected to be very brief.
When the presentation of the fetus at the cervix will permit injection of agents like pentobarbitone, ketamine or
xylazine, sufficient time should be given for them to act before fetotomy. Making such an injection can be very
difficult when the uterus is tightly contracted around a fetus which is awkwardly positioned in relation to the cervix,
and can lead to practitioners injecting themselves or the cow. Provided they can be done safely, such injections
13
should be attempted, especially when a throat cut or decapitation is not possible before cutting away another body
part, and best practice would dictate that they should precede a throat cut and decapitation as well.
Fetotomy is sometimes required when an almost fully delivered, breathing and aware calf has its hind quarters
wedged in the dam’s pelvis. Such young must be killed before fetotomy, preferably using the best practice approach
just noted.
Discussion
From the evidence outlined in this review, one can piece together the factors that bring about behavioural arousal and
awareness when a lamb is born. During the lead-up to parturition, the fetus is exposed to progressively lower
circulating levels of progesterone and its metabolites and to an acute rise in oestrogen concentrations. These changes
act to enhance behavioural arousal, which, at the time of delivery, is provoked by five factors. These factors are
physical stimulation of the face and ears as the fetus passes along the birth canal, severance of the umbilical cord,
hypoxaemia/hypercapnia arising from cord severance, sudden loss of an arousal-inhibiting factor normally released
by the placenta, and eventually, increased oxygenation brought about by the onset of breathing following delivery.
It is likely that a crucial prerequisite of awareness is the increased oxygenation that occurs once the newborn starts to
breathe air. The normal levels of O2 in the circulations of the fetal lamb and of the newborn before it starts to
breathe air, are apparently below those required to support awareness in the neonate and adult. This means that,
under normal circumstances, it is improbable that the fetus could experience perceptual awareness before it is
delivered. If so, it is only after the onset of breathing that the brain would receive blood that contains sufficient O 2 to
support awareness.
However, there is no direct evidence which proves that fetuses remain unaware and unable to experience pain
throughout pregnancy. It can be argued that the greater capacity of fetal as opposed to adult haemoglobin to deliver
O2 to tissues at low O2 tensions (Meschia et al 1961), the higher haematocrit (Meschia et al 1965) and the higher rate
of blood perfusion through fetal tissues (Rudolph et al 1981; Rudolph 1984) may be sufficient to support fetal
awareness, or it may confer on the fetus the capacity to be aroused to an aware state during noxious (e.g. surgical)
stimulation.
It would be difficult to test this.
Nevertheless, it would be helpful in the future to test for
responsiveness in cortical regions of the brain associated with perceptual awareness, using neural imaging
techniques. This could add to our understanding of the likelihood of fetal perceptual awareness.
Physical activity in a fetus can be disconcerting when it occurs in response to manipulation of the pregnant animal,
for example during surgery or slaughter. However, provided the mother has not been super-oxygenated, and
provided the fetus is prevented from breathing air, the analysis in this review suggests that physical activity is not a
major cause for concern about the welfare of fetuses. This is especially so when the manipulation is associated with
marked fetal hypoxaemia. At slaughter, the rapid onset of cerebral hypoxia/anoxia in the fetus is terminal and
ensures that fetuses do not suffer, whether or not their blood (serum) is collected. On the other hand, where the aim
is to deliver live newborns, it is important that normal breathing be established as soon as possible after the umbilical
cord has been severed. Some slaughtermen occasionally try to salvage fetuses on the slaughterboard, which they
14
hope to hand-rear. This practice carries risks, as the period of hypoxaemia experienced by the fetus before it is taken
from the uterus of the dead mother may be too protracted to permit it to survive for long.
In situations where a fetotomy has to be conducted, the primary concern should be the survival and welfare of the
dam. Some practitioners favour performing a Caesarean section over a fetotomy when the fetus is still alive.
Bearing in mind that the reasoned conclusion from this review is that the fetus is not likely to be in a position to
suffer until it breathes air, especially if it is severely hypoxaemic, it is suggested that the decision to do a Caesarean
or a fetotomy should be based primarily on welfare considerations for the dam rather than the fetus. In particular, the
focus should be on the post-operative pain and discomfort the dam is likely to experience following either procedure.
An additional factor is the practitioner’s skill with both procedures, the welfare consequences of a well executed
fetotomy generally being preferable to those of a badly completed Caesarean, and a Caesarean done well being
preferable to a poorly executed fetotomy.
In general terms, sheep are precocial animals at birth. The newborn lamb is behaviourally and neurologically welladvanced, and this provides it with survival advantages. The concepts about the physiology of the development of
behavioural arousal and awareness described in this review are also likely to apply to other livestock species, and in
particular to those which are at a comparable stage of neural development by the end of pregnancy.
Acknowledgements
We are particularly grateful to the following people for helpful discussion during the long gestation period of this
review: Alistair Gunn and Jane Harding (Auckland University), Carina Mallard and Sandra Rees (Melbourne
University), Philip Berger, Richard Harding, Adrian Walker, David Walker and Ross Young (Monash University),
Howard Tyler (Iowa State University), Cheryl McMeekan, Kevin Stafford and Jos Vermunt (Massey University),
and David Bayvel (Ministry of Agriculture and Forestry). We also thank MAF for financial support.
References
Adamson SL, Richardson BS, Homan J. Initiation of pulmonary gas exchange by fetal sheep in utero. Journal of
Applied Physiology 62, 989-98, 1987
Adamson SL, Kuipers IM, Olson DM. Umbilical cord occlusion stimulates breathing independent of blood gases
and pH. Journal of Applied Physiology 70, 1796-1809, 1991
Akerstedt T, Hume K, Minors D, Waterhouse J. Experimental separation of time of day and homeostatic
influences on sleep. American Journal of Physiology: Regulation, integrative and Comparative Physiology
274, R1162-8, 1998
Alexander G. Husbandry practices in relation to maternal and offspring behaviour. In: Wodzicka-Tomaszewska M,
Edey TN, Lynch JJ (eds). Behaviour – Reviews in Rural Science, Behaviour in Relation to Reproduction,
Management and Welfare of Farm Animals 4, 99-107. University of New England Press, Armidale, 1980
15
Alvaro R, de Almeida V, Al-Alaiyan S, Robertson M, Nowacsyk B, Cates D, Rigatto H. A placental extract
inhibits breathing induced by umbilical cord occlusion in fetal sheep. Journal of Developmental Physiology
19, 23-8, 1993
Baars BJ. There are no known differences in brain mechanisms of consciousness between humans and other
mammals. Animal Welfare 10, S31-40, 2001
Baier RJ, Hasan SU, Cates DB, Hooper B, Nowaczyk B, Rigatto H. Effects of various concentrations of O2 and
umbilical cord occlusion on fetal breathing and behavior. Journal of Applied Physiology 68, 1597-1604, 1990
Barcroft J, Barron DH. Movements in midfoetal life in the sheep embryo. Journal of Physiology 91, 329-51, 1937
Barcroft J, Barron DH. The development of behaviour in foetal sheep. Journal of Comparative Neurology 70,
477-502, 1939
Barcroft J, Kennedy JA, Mason MF. Oxygen in the blood of the umbilical vessels of sheep.
Journal of
Physiology 97, 347-56,1940
Barlow RM. The fetal sheep: morphogenesis of the nervous system and histochemical aspects of myelination.
Journal of Comparative Pathology 135, 249-62, 1969
Bassett JM, Oxborrow TJ, Smith ID, Thorburn GD. The concentration of progesterone in the peripheral plasma
of the pregnant ewe. Journal of Endocrinology 45, 449-57, 1969
Barron DH, Meschia G. The carbon dioxide gradient between the foetal and maternal bloods of sheep and goats.
Yale Journal of Biology and Medicine 29, 480-95, 1957
Berger PJ, Walker AM, Horne R, Brodecky V, Wilkinson MH, Wilson F, Maloney JE. Phasic respiratory
activity in the fetal lamb during late gestation and labour. Respiratory Physiology 65, 55-68, 1986
Berger PJ, Horne RSC, Soust M, Walker AM, Maloney JE. Breathing at birth and the associated blood gas and
pH changes in the lamb. Respiratory Physiology 82, 251-66, 1990
Berger PJ, Kyriakides MA, Cooke IRC. Supraspinal influence on the development of motor behavior in the fetal
lamb. Journal of Neurobiology 33, 276-88, 1997
Bernhard, C.G. and Meyerson, B.A. Morphological and physiological aspects of the development of recipient
functions in the cerebral cortex. In: R.S. Comline, K.W. Cross, G.S. Dawes and P.W. Nathanielsz (eds).
Fetal and Neonatal Physiology. Pp 1-19. Cambridge University Press, 1973
Bocking AD, Harding R. Effects of reduced uterine blood flow on electrocortical activity, breathing, and skeletal
muscle activity in fetal sheep. American Journal of Obstetrics and Gynecology 154, 655-62, 1986
Bocking AD, Gagnon R, Milne KM, White SE. Behavioural activity during prolonged hypoxemia in fetal sheep.
Journal of Applied Physiology 65, 2420-6, 1988
Boddy K, Dawes GS, Fisher R, Pinter S, Robinson JS. Foetal respiratory movements, electrocortical and
cardiovascular responses to hypoxaemia and hypercapnia in sheep. Journal of Physiology 243, 599-618,
1974
Brierly JB, Prior DF, Calverly J, Jackson SJ, Brown AW. The pathogenesis of ischaemic neuronal damage along
the cerebral arterial boundary zone in Papio anubis. Brain 103, 929-45, 1980
Challis JRG, Patrick JE. Fetal and maternal oestrogen concentrations throughout pregnancy in sheep. Canadian
Journal of Physiology and Pharmacology 59,970-8, 1981
Clapp JF, Peress NS, Wesley M, Mann LI. Brain damage after intermittent partial cord occlusion in the
chronically instrumented fetal lamb. American Journal of Obstetrics and Gynecology 159, 504-9, 1988
Clewlow F, Dawes GS, Johnston BM, Walker DW. Changes in breathing, electrocortical and muscle activity in
the unanaesthetized fetal lamb with age. Journal of Physiology 341, 463-76, 1983
16
Comline RS, Silver M. Daily changes in foetal and maternal blood of conscious pregnant ewes with catheters in
umbilical and uterine vessels. Journal of Physiology 209, 567-86, 1970
Comline RS, Silver M. The composition of foetal and maternal blood during parturition in the ewe. Journal of
Physiology 222, 233-56, 1972
Cook CJ, Gluckman PD, Johnston BM, Williams C. The development of the somatosensory evoked potentials in
the unanaesthetised fetal sheep. Journal of Developmental Physiology 307, 335-53, 1987
Crenshaw MC, Meschia G, Barron, DH. Role of progresterone in inhibition of muscle tone and respiratory rhythm
in foetal lambs. Nature 212, 842, 1966
Crossley KJ, Nicol MB, Hurst JJ, Walker DW, Thorburn GD. Suppression of arousal by progesterone in fetal
sheep. Reproduction Fertility and Development 9, 767-73, 1997
Dawes GS (1988). The 1987 James A.F. Stevenson Memorial Lecture. The development of fetal behavioural
patterns. Canadian Journal of Physiology and Pharmacology 66, 541-8, 1988
Dawes GS, Fox HE, Richards RT. Variations in asphyxial gasping with age in lambs and guinea-pigs. Quarterly
Journal of Experimental Physiology 57, 131-8, 1972a
Dawes GS, Fox HE, Leduc BM, Liggins GC, Richards RT. Respiratory movements and rapid eye movement
sleep in the foetal lamb. Journal of Physiology 220, 119-43, 1972b
de Haan HH, Gunn AJ, Gluckman PD. Experiments in perinatal medicine: what have we learnt? Prenatal and
Neonatal Medicine 1, 16-25, 1996
Dolling M, Seamark RF. Progesterone metabolites in fetal sheep plasma: the effect of nephrectomy. Journal of
Developmental Physiology 1, 399-413, 1979
Dufty JH, Sloss V. Anoxia in the bovine foetus. Australian Veterinary Journal 53, 262-7, 1977
Eales FA, Small J. Summit metabolism in newborn lambs. Research in Veterinary Science 29, 211-8, 1980
Eales FA, Small J. Effects of acute hypoxia on heat production capacity and summit metabolism in newborn lambs.
Research in Veterinary Science 39, 212-15, 1985
Eales FA, Small J. Practical lambing and lamb care - a veterinary guide (2nd edition). Longman Group Ltd, 1995
Eisele JH, Eger EI, Muallem M. Narcotic properties of carbon dioxide in the dog. Anesthesiology 28, 856-65,
1967
Empson J. Sleep and Dreaming (2nd Ed.). Pp 22-39. Harvester Wheatsheaf, New York, 1993
Endo T, Roth C, Landolt H-P, Werth E, Aeschbach D, Achermann P, Borbely AA. Selective REM sleep
deprivation in humans: effects on sleep and sleep EEG. American Journal of Physiology: Regulatory,
Integrative and Comparative Physiology 274, R1186-94, 1998
Fewell JE, Konduri GG. Repeated exposure to rapidly developing hypoxemia influences the interaction between
oxygen and carbon dioxide in initiating arousal from sleep in lambs. Pediatric Research 24, 28-33, 1988
Fewell JE, Konduri GG. Influence of repeated exposure to rapidly developing hypoxaemia on the arousal and
cardiopulmonary response to developing hypoxaemia in lambs. Journal of Developmental Physiology 11,
77-82, 1989
Fitzgerald M. Development of somatosensory function. In: Eds. Gluckman PD, Heyman MA. Pediatrics and
Perinatology (2nd edition). Pp 379-82. Arnold (Hodder Headline Group), Auckland, 1996
Fitzgerald M. Development and neurobiology of pain. In: Wall PD, Melzack R. (eds). Textbook of Pain. (4th
edition). Pp 235-51. Churchill Livingstone, Edinburgh, 1999
Fraser AF. The phenomenon of pandiculation in the kinetic behaviour of the sheep fetus.
Behaviour Science 24, 169-82, 1989
17
Applied Animal
Fraser AF, Broom DM. Farm animal behaviour and welfare. Pp 198-207, 227-38, 247-55. Beilliere Tindall,
London, 1990
Gluckman PD, Gunn TR, Johnston BM, Quinn JP. Manipulation of the temperature of the fetal lamb in utero. In:
Nathanielsz PW (ed). Animal Models in Fetal Medicine (IV). Pp 37-56. Perinatology Press, Ithaca, New
York, 1984
Gluckman PD, Johnston BM, Nathanielsz PW. (eds). Advances in fetal physiology: reviews in honour of G.C.
Liggins. Advances in Perinatal Medicine (VII). Pp 1-420. Perinatology Press, Ithaca, New York, 1989
Gluckman PD, Gunn TR, Johnston BM. The effect of cooling on breathing and shivering in unanaesthetised fetal
lambs in utero. Journal of Physiology 343, 495-506, 1993
Gregory NG, Wilkins LJ. Effect of cardiac arrest on susceptibility to carcass bruising in sheep. Journal of Science
of Food and Agriculture 35, 671-6, 1984
Gregory NG, Wotton SB. Sheep slaughtering procedures. II. Time to loss of brain responsiveness after
exsanguination or cardiac arrest. British Veterinary Journal 140, 354-60, 1984
Gunn AJ, Parer JT, Mallard EC, Williams CE, Gluckman PD. Cerebral histologic and electrocorticographic
changes after asphyxia in fetal sheep. Pediatric Research 31, 486-91, 1992
Gunn AJ, Gluckman PD, Gunn TR. Selective head cooling in newborn infants after perinatal asphyxia: a safety
study. Pediatrics 102, 885-902, 1998
Gunn TR, Johnston BM, Iwamoto HS, Fraser M, Nicholls MG, Gluckman PD. Haemodynamic and
catecholamine responses to hypothermia in the fetal sheep in utero. Journal of Developmental Physiology 7,
241-9, 1985
Gunn TR, Butler J, Gluckman PD. Metabolic and hormonal responses to cooling the fetal sheep in utero. Journal
of Developmental Physiology 8, 55-66, 1986
Gunn TR, Ball KT, Gluckman PD. Reversible umbilical cord occlusion: Effects on thermogenesis in utero.
Pediatric Research 30, 513-7, 1991
Harding JE, Jones CT, Robinson JS. Studies on experimental growth retardation in sheep. The effects of a small
placenta in restricting transport to and growth of the fetus. Journal of Developmental Physiology 7, 427-42,
1985
Harding R, Poore ER, Cohen GL. The effect of brief episodes of diminished uterine blood flow on breathing
movements, sleep states and heart rate in fetal sheep. Journal of Developmental Physiology 3, 231-43, 1981
Hart R, Mackay JMK, McVittie CR, Mellor DJ. A technique for the derivation of lambs by hysterectomy.
British Veterinary Journal 127, 419-24, 1971
Hasan SU, Rigaux A. The effects of lung distension, oxygenation, and gestational age on fetal behavior and
breathing movements in sheep. Pediatric Research 30, 193-201, 1991
Hattingh J, Cornelius ST, Ganhao MF, Fonseca F. Arterial blood gas composition, consciousness and death in
rabbits. Journal of the South African Veterinary Association 57, 13-16, 1986
Hirst JJ, Egodagamage KC, Walker DW. Effect of neuroactive steroid infused into the cerebral ventricles of fetal
sheep in utero using small infusion volumes. Journal of Neuroscience Methods 97, 37-44, 2000
Horne RSC, Berger PJ, Bowes G, Walker AM. Effect of sinoaortic denervation on arousal responses to
hypotension in newborn lambs. American Journal of Physiology 256, H434-40, 1989
Jansen AH, Ioffe S, Russell BJ, Chernick V. Influence of sleep state on the response to hypercapnia in fetal lambs.
Respiratory Physiology 48, 125-42, 1982
Jensen A, Hohmann M, Kunzel W. Dynamic changes in organ blood flow and oxygen consumption during acute
asphyxia in fetal sheep. Journal of Developmental Physiology 9, 41-55, 1987
18
Jensen A, Roman Ch, Rudolph AM. Effect of reducing uterine blood flow on fetal blood flow distribution and
oxygen delivery. Journal of Developmental Physiology 15, 309-23, 1991
Jochems, CEA, ven der Valk JBF, Stafleu FR and Baumans V. The use of fetal bovine serum: ethical or
scientific problem? Alternatives to Laboratory Animals 30, 219-227, 2002
Johnston RV, Grant DA, Wilkinson MH, Walker AM. Repetitive hypoxia depresses arousal from active sleep in
newborn lambs. Journal of Physiology 510, 651-9, 1998
Jones CT. The development of some metabolic responses to hypoxia in the foetal sheep. Journal of Physiology
265, 743-62, 1977
Jones CT, Boddy K, Robinson JS, Ratcliffe JG. Developmental changes in the responses of the adrenal glands of
foetal sheep to endogenous adrenocorticotrophin, as indicated by hormone responses to hypoxaemia. Journal
of Endocrinology 72, 279-92, 1977
Kent JE, Molony V, Graham MJ. Comparison of methods for the reduction of acute pain produced by rubber ring
castration or tail docking of week-old lambs. The Veterinary Journal 155, 39-51, 1998
King KJ, McCullagh P. Splenectomy of the fetal lamb early in development as a model of congenital asplenia.
Australian & New Zealand Journal of Surgery 71, 41-5, 2001
Kirkwood JK, Hubrecht RC, Wickens S, O’Leary H, Oakeley S (eds.) Consciousness, cognition and animal
welfare. Animal Welfare 10 Suppl, S1-251, 2001
Ladds PW, Summers PM, Humphrey JD. Pregnancy in slaughtered cows in north-eastern Australia. Australian
Veterinary Journal 51, 472-7, 1975
Landolt H-P, Raimo EB, Schierow BJ, Kelsoe JR, Rapaport MH, Gillin JC. Sleep and sleep
electroencephalogram in depressed patients treated with phenelzine. Archives of General Psychiatry 58, 26876, 2001
Lehman H Animal awareness. Applied Animal Behaviour Science 57, 315-25, 1998
Liggins GC, Faircough RT, Grieves SA, Kendall JZ, Knox BS. The mechanism of initiation of parturition in the
ewe. Recent Progress in Hormone Research 29, 111- 59, 1973
Lynch JJ, Hinch GN, Adams DB. The behaviour of the lamb. In: The Behaviour of Sheep: Biological Principles
and Implications for Production. Pp 153-77. CAB International and CSIRO Australia, 1992
Mallard EC, Gunn AJ, Williams CE, Johnston BM, Gluckman PD. Transient umbilical cord occlusion causes
hippocampal damage in the fetal sheep. American Journal of Obstetrics and Gynecology 167, 1423-30, 1992
Mann LI, Prichard JW, Symmes D. EEG, ECG, and acid-base observations during acute fetal hypoxia. American
Journal of Obstetrics and Gynecology 106, 39-51, 1970
Mattsson JL, Stinson JM, Clark CS. Electroencephalographic power-spectral changes coincident with onset of
carbon dioxide narcosis in rhesus monkey. American Journal of Veterinary Research 33, 2043-9, 1972
Mellor DJ. Vascular anastomosis and fusion of foetal membranes in multiple pregnancy in sheep. Research in
Veterinary Science 10, 361-367, 1969
Mellor DJ. Investigations of the fluid spaces of the sheep conceptus. In: Nathanielsz PW (ed). Animal Models in
Fetal Medicine (I). Pp 59-106. Elsevier/North Holland, 1980
Mellor DJ. Nutritional and placental determinants of fetal growth rate in sheep and consequences for the newborn
lamb. British Veterinary Journal 139, 307-24, 1983
Mellor DJ. Investigations of fetal growth in sheep. In: Nathanielsz PW (ed). Animal Models in Fetal Medicine (IV).
Pp 149-73. Perinatology Press, Ithaca, New York, 1984
Mellor DJ. Feeding pregnant ewes and newborn lambs during experiment. In: Nathanielsz PW (ed). Animal Models
in Fetal Medicine (VI). Pp 55-92. Perinatology Press, Ithaca, New York, 1987
19
Mellor DJ. Integration of perinatal events, pathophysiological changes and consequences for the newborn lamb.
British Veterinary Journal 144, 552-69, 1988
Mellor DJ, Cockburn F. A comparison of energy metabolism in the newborn infant, piglet and lamb. Quarterly
Journal of Experimental Physiology 71, 361-79, 1986
Mellor DJ, Murray L. Effects of tail docking and castration on behaviour and plasma cortisol concentrations in
young lambs. Research in Veterinary Science 46, 387-91, 1989
Mellor DJ, Pearson RA. Some changes in the composition of blood during the first 24 hours after birth in normal
and growth retarded lambs. Annales de Recherches Veterinaires 8, 460-7, 1977
Mellor DJ, Slater JS. Daily changes in amniotic and allantoic fluid during the last three months of pregnancy in
conscious, unstressed ewes with catheters in their foetal fluid sacs. Journal of Physiology 217, 573-604, 1971
Mellor DJ, Stafford KJ. Animal welfare implications of neonatal mortality and morbidity in farm
animals. Applied Animal Behaviour Science (submitted).
Mellor DJ, Mackay JMK, Williams JT. Effects of oestrogen on activity and survival of lambs delivered by
hysterectomy. Research in Veterinary Science 13, 399-401, 1972
Meschia G, Hellegers A, Blechner JN, Wolkoff AS, Barron DH. A comparison of the oxygen dissociation curves
of the bloods of maternal, foetal and newborn sheep at various pHs. Quarterly Journal of Experimental
Physiology 46, 95-100, 1961
Meschia G, Cotter JR, Breathnach CS, Barron DH. The haemoglobin, oxygen, carbon dioxide and hydrogen ion
concentrations in the umbilical bloods of sheep and goats as sampled via plastic indwelling catheters.
Quarterly Journal of Experimental Physiology 50, 185-95, 1965
Mohan Raj AB, Wotton SB, Gregory NG. Changes in the somatosensory evoked potentials and spontaneous
electroencephalogram of hens during stunning with a carbon dioxide and argon mixture. British Veterinary
Journal 148, 147-56, 1992
Mott JC. Ability of young animals to withstand total oxygen lack. British Medical Bulletin 17, 144-8, 1961
Newhook JC, Blackmore DK. Elecetroencephalographic studies of stunning and slaughter of sheep and calves:
Part 1 – The onset of permanent insensibility in sheep during slaughter. Meat Science 6, 221-33, 1982
Nicol MB, Hurst JJ, Walker DW, Thorburn GD. Effect of alteration of maternal plasma progesterone
concentrations on fetal behavioural state during late gestation. Journal of Endocrinology 152, 379-86, 1997
Nicol MB, Hurst JJ, Walker DW. Effect of pregnane steroids on electrocortical activity and somatosensory evoked
potentials in fetal sheep. Neuroscience Letters 253, 111-4, 1998
Nitsos I, Rees S. Development of immunoreactivity for calcitonin gene-related peptide, substance P and glutamate in
primary sensory neurons, and for serotonin in the spinal cord of fetal sheep. Neuroscience 54, 239-52, 1993
Nitsos I, Sexton PM, Rees S. The ontogeny of [125I]rat--CGRP binding sites in the spinal cord of sheep: a prenatal
and postnatal study. Neuroscience 62, 257-64, 1994
Pallis C. Reappraising death. British Medical Journal 285: 1409-12, 1982
Paul SM, Purdy RH. Neuroactive steroids. Federation of American Society of Experimental Biology Journal 6,
2311-22, 1992
Pearson RA, Mellor DJ. Some physiological changes in pregnant sheep and goats before, during and after surgical
insertion of uterine catheters. Research in Veterinary Science 19, 102-4, 1975
Persson HE. Functional development in the somatosensory cortex of foetal sheep. In: Comline RS, Cross KW,
Dawes GS, Nathanielsz PW (Eds.). Fetal and Neonatal Physiology. Pp 20-7. Cambridge University Press,
1973
20
Piggins D, Phillips CJC. Awareness in domesticated animals – concepts and definitions.
Applied Animal
Behaviour Science 57, 181-200, 1998
Pinheiro Machado FLC, Hurnik JF, Burton JH. The effect of amniotic fluid ingestion on the nociception of
cows. Physiology & Behavior 62,1339-44, 1997
Power SGA, Patrick JE, Carson GD, Challis JRG. The fetal membranes as a possible source of progesterone in
the amniotic and allantoic fluids of pregnant sheep. Endocrinology 110, 481-6, 1982
Rees S, Nitsos I, Rawson J. The development of cutaneous afferent pathways in fetal sheep: a structural and
functional study. Brain Research 661, 207-22, 1994a
Rees S, Rawson J, Nitsos I, Brumley C. The structural and functional development of muscle spindles and their
connections in fetal sheep. Brain Research 642, 185-98, 1994b
Richardson BS, Carmichael L, Homan J, Johnston L, Gagnon R. Fetal cerebral, circulatory, and metabolic
responses during heart rate decelerations with umbilical cord compression. American Journal of Obstetrics
and Gynecology 175, 929-36, 1996
Richardson BS, Carmichael L, Homan J, Patrick JE. Electrocortical activity, electroocular activity, and breathing
movements in fetal sheep with prolonged and graded hypoxemia. American Journal of Obstetrics and
Gynecology 167, 553-8, 1992
Rigatto H, Blanco CE, Walker DW. The response to stimulation of hindlimb nerves in fetal sheep, in utero, during
the different phases of electrocortical activity. Journal of Developmental Physiology 4, 175-85, 1982
Rigatto H, Lee D, Davi M, Moore M, Rigatto E, Cates D. Effect of increased arterial CO2 on fetal breathing and
behaviour in sheep. Journal of Applied Physiology 64, 982-7, 1988
Robinson JS, Kingston EJ, Jones CT, Thorburn GD. Studies on experimental growth retardation in sheep. The
effect of removal of endometrial caruncles on fetal size and metabolism.
Journal of Developmental
Physiology 1, 379-98, 1979
Robinson JS, Jones CT, Kingston EJ. Studies on experimental growth retardation in sheep. The effects of
maternal hypoxaemia. Journal of Developmental Physiology 5, 89-100, 1983
Ruckebusch Y, Gaujoux M, Eghbali B. Sleep cycles and kinesis in the fetal lamb. Electroencephalographic &
Clinical Neurophysiology 42, 226-37, 1977
Rudolph AM. The fetal circulation and its response to stress. Journal of Developmental Physiology 6, 11-19, 1984
Rudolph AM, Itskovitz J, Iwamoto H. Reuss ML, Heymann M. Fetal cardiovascular responses to stress.
Seminars in Perinatology 5, 109-21, 1981
Seamark RF, Nancarrow CD, Gardner J. Progesterone metabolism in ovine fetal blood: the formation of 3hydroxy-pregn-4-en-20-one and other substances. Steroids 15, 589-603, 1970
Sieker HO, Hickam JB. Carbon dioxide intoxication: the clinical syndrome, its etiology and management with
particular reference to the use of mechanical respirators. Medicine 35, 389-423, 1956
Silver M, Steven BH, Comline RS. Placental exchange and morphology in ruminants and mare. In: Comline RS,
Cross KW, Dawes GS, Nathanielsz PW (Eds.). Fetal and Neonatal Physiology. Pp 245-71. Cambridge
University Press, 1973
Slee J, Springbett A. Early postnatal behaviour in lambs of ten breeds. Applied Animal Behaviour Science 15, 22940, 1986
Sommerville BA, Broom DM. Olfactory awareness. Applied Animal Behaviour Science 57, 269-86, 1998
Thorburn GD, Challis JRG. Endocrine control of parturition. Physiological Reviews 59, 877-88, 1979
Tyler H and Ramsey H. Hypoxia in neonatal calves: effect on selected metabolic parameters. Journal of Dairy
Science 74, 1957-1962, 1991
21
Villiger JW, Taylor KM, Gluckman PD. Multiple benzodiazapine receptors in the ovine brain: ontogeny,
properties, and distribution of 3H-diazapam binding. Paediatric Pharmacology 2, 179-87, 1982
Walker AM, Carroll J, de Preu ND, Horne RSC. Modification of arousal responses following hypoxia in
newborn lambs. In: Walker AM, McMillan C, National SIDS Council (eds). Second SIDS International
Conference and First SIDS Global Strategy Meeting. Pp. 238-42. Perinatology Press, New York, 1993
West JB, Hackett PH, Maret KH, Milledge JS, Peters RM, Pizzo CJ, Winslow RM. Pulmonary gas exchange
on the summit of Mt. Everest. Journal of Applied Physiology 55, 678-87, 1984
22
Table 1: Summary of Suppressors and Activators of Fetal Behavioural Arousal
Suppressors
 fetal blood oxygen and/or  blood carbon dioxide levels.
 fetal blood levels of progesterone and progesterone metabolites.
 fetal body and skin temperature – warmth.
 fetal somatosensory stimulation.
 placental inhibitor of arousal and breathing.
Activators
 fetal and newborn blood oxygen levels.
 fetal and newborn blood levels of oestrogens.
 fetal and newborn skin temperature activating cold thermoreceptors.
 fetal and newborn somatosensory stimulation (tactile, gravitational).
23