Lesson-5.THE OESTRUS CYCLE
The estrus cycle is defined as the time between periods of estrus. The average length of
the estrous cycle is similar for all farm species. It is about 17 days for the Ewe,21 days
for the Cow and Doe,22 days for the Mare and 20 days for the Sow. Individual variation
is seen in all species. Estrous cycles ranging from 17 to 24 days are considered normal in
the cow and a range of 19 to 25 days is reported in the Mare. While variation among
individuals of a particular species is expected, variable cycles for one individual may
indicate an abnormality.
Oestrus cycle in different species of animals
Cow
Ewe
Estrous cycle(days )
21
17
Metestrus
(days)
3-4
Diestrus
Estrus
Ovulation
( Days )
Sow
20
2-3
2-3
10-14
10-12
18-24 hrs
24-36hrs
10-12hrs
late estrus
after estrus
11-13
48-72hrs
mid
estrus
Mare
22
Doe
21
2-3
2-3
10-12
4-8days
1-2 days
before
estrus ends
13-15
30-40hrs
Few
hours
after estrus
Periods of the estrous cycle:
The periods of estrous cycle are estrus, Metestrus, Diestrus and Proestrus. These periods
occur in a cyclic and sequential manner except for periods of anoestrus (absence of
cycling) in seasonal breeders such as the ewe, doe and mare, as well as anestrus during
pregnancy and the early post partum period for all species.
Period
Estrus
Metestrus
Diestrus
Proestrus
days
1
2-4
5-16
17-21
principal features
Behavioral signs of estrus
Ovulation
Corpus luteum function
Rapid follicle growth
Figure. The Oestrus cycle.
Figure. Ovarian changes during the oestrus cycle
Estrus:
is defined as the period of time when the female is receptive to the male and will stand
for mating. The duration of estrus in different species of animals is given in table….
Changes in the reproductive organs and behaviour of the animal are brought about by the
effect of Oestrodiol on the brain and the reproductive organs.
Internal signs of estrus.
 The uterus become enlarged and tonic
 The cervice become enlarged and open
 Graffian follicle can be palpated, mostly on the right ovary
Behavioral signs of estrus:
Early heat




will not stand to be
ridden -smells other
cows
attempts to ride
other cows
vulva moist, red and
slightly swollen
restless and bellows
Standing heat






stands to be ridden
nervous
and
excitable
rides other cows
may hold up milk
vulva moist and red
clear
mucus
discharge
Figure 5. Signs and stages of the Oestrus
Late Heat



will not stand to be
ridden
smells other cows
clear
mucus
discharge
from
vulva
Metestrus:
The period of metestrus begins with the cessation of estrus and lasts for about 3
days. Primarily, it is a period of formation of the corpus luteum. However,ovulation
occurs during this period in Cows and does. Also, a phenomenon known as metestrous
bleeding occurs in cows, appearing in about 90% of all metestrus periods in heifers and
45% in mature cows. During late proestrus and estrus, high estrogen concentrations
increase the vascularity of the endometrium, this vascularity reaching its peak about 1
day after the end of estrus. With declining levels, some breakage of capillaries may
occur, resulting in a small loss of blood. This will be noticed as a patch of blood on the
tail approximately 35-45 hours after the end of estrus. It is not an indication of conception
or of a failure to conceive.
Diestrus:
is characterised as the period in the cycle when the corpus luteum is fully
functional. In the cow it starts about day 5 of the cycle, when an increase in blood
concentration of progesterone can first be detected and ends with regression of the corpus
luteum on day 16 or 17. It has been called the period of preparation of the uterus for
pregnancy.
Proestrus:
Proestrus begins with the regression of the corpus luteum and drop in progesterone and
extends to the start of the estrus. The principal distinguishing feature of proestrus is the
occurance of rapid follicle growth and maturation. Late during this period the effects of
estrogen on the duct system and behavioral symptoms of approaching estrus can be
observed.
Classification of Animal based on oestrus cycle.
Monoestrusanimals
Animals whichhas one oestrus cycle per year. Eg- wild
Polyoestrus
Animals which has frequent periodic oestrus
cyclethroughout the year.- Eg- Cattle,pig, mare, etc.
Seasonal polyoestrus-
Animal which have periodic oestrus cycle during certain
season of the year- Sheep, Yak
The bitch and queens are more nearly like the monoestrus animals. The bitch may have 24 periods of oestrus each year
Estrus Detection in farm animals.
Estrus detection methods falls in three broad categories.
1. Physical methods.
This further includes
 Observation of the External signs of signs of estrus- This could be done once
in the morning and once in the evening.
 Use of teasers- Teaser bulls ( Vesectomized).
 Use of paints. – tail Paints
 Rectal temperature- 2 –3 0 C higher
2. Per rectal method
Palpation of enlarged. tonic uterus, enlarged and dilated cervix, Graffian follicle on
the ovary.
3. Hormonal assay- measuring the milk progesterone level- < 2 ug/ml indicates
Estrus.
Figure . changes in blood plasma hormones concentration during oestrus cycle
_________( oestradiol) ----------- ( Progesterone)
Figure. Hormonal picture during the oestrus cycle.