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Carcass and meat quality of Assaf milk fed lambs: effect of rearing
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system and sex
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*Rodríguez, A.B., Landa, R., Bodas, R., Prieto, N., Mantecón, A.R.,
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Giráldez, F.J.
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Estación Agrícola Experimental (CSIC). Finca Marzanas, 24346-Grulleros, León (Spain)
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* Corresponding author: Tel. (34) 987 31 71 56; Fax (34) 987 31 71 61
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E-mail address: rganabel@hotmail.com
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Abstract
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The effect of sex and rearing system on growth and carcass and meat characteristics of milk-
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fed Assaf lambs was studied. Thirty-six lambs, 18 males and 18 females were used. Twelve
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lambs remained with their mothers throughout the experiment (NR). Within 24-36 hours of
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birth, the rest were housed individually and fed twice a day ad libitum (AAR) or at 70% of ad
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libitum consumption (RAR) with reconstituted cow milk. Sex did not affect animal
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performance, yet females showed higher carcass and non carcass fat deposits. NR lambs
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showed greater BWG than AAR fed lambs, and AAR, higher than the RAR. Differences
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between naturally and artificially reared lambs in CCW and killing out percentage were not
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significant. Empty digestive tract and mesenteric fat weights were greater for RAR than NR
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lambs, with the AAR lambs demonstrating intermediate values; conversely, omental fat was
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greater in NR lambs. Carcass ether extract content was greater for NR lambs, possibly due to
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the greater growth. Use of ad libitum cow’s milk substitute in suckling lambs twice a day
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resulted in less body weight gain but similar killing out percentages than naturally raised
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lambs. A 70% restricted supply increased the days in suckling and reduced carcass fatness
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and compactness. Except for water loss, which was less in NR than artificially fed lambs, no
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differences were found in meat characteristics.
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Keywords: Lamb; naturally; artificially milk feeding system; growth, carcass, non carcass,
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meat quality.
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Introduction
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Traditionally, in the Mediterranean countries of EU, most dairy sheep systems produce lambs
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aimed at 10 kg live weight. This type of lamb is a very valuable product due to its appreciated
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organoleptic qualities. In Spain during many decades, Churra and Castellana were the most
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important dairy breeds and hence most of milk fed lambs were from these breeds.
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Nevertheless, in the last twenty years the population of local dairy breeds has greatly
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decreased whereas the population of foreign breeds, such as Awassi or Assaf, has increased
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(Ugarte, Ruiz, Gabiña, & Beltrán de Heredia, 2001). Currently, the Assaf breed is becoming
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the most important dairy sheep breed in a number of Spanish regions and, at this moment, its
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population is estimated to be around 800,000 animals (Ugarte et al., 2001). In consequence of
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this, lamb meat production of this foreign breed has significantly increased.
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It is well known that ewe genotype could have a significant effect on lamb performance and
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carcass and meat quality (Sañudo, Campo, Sierra, María, Olleta, & Santolaria, 1997; Beriaín,
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Horcada, Purroy, Lizaso, Chasco, & Mendizabal, 2000; Santos-Silva, Mendes, & Bessa,
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2002). Different authors have analysed the growth and carcass and meat characteristics of fat-
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tailed lambs, and the Awassi is one of the most studied (Macit, Esenbuga, & Karaoglu, 2002;
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Titi, Dmour, & Abdullah, 2007).
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Likewise, comparative studies of Awassi and Spanish dairy breeds have been carried out and
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differences in parameters such as killing out percentage, carcass conformation, meat colour or
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cooking losses have been reported (Sañudo et al., 1997). Nevertheless, to the best of our
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knowledge, there are not many published data on performance and carcass and meat quality of
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Assaf lambs.
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In addition to genotype, animal performance and meat quality can also be affected by rearing
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system (Napolitano, Braghieri, Cifuni, Pacelli, & Girolami, 2002a; Napolitano, Cifuni,
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Pacelli, Riviezzi, & Girolami, 2002b; Osorio, Zumalacárregui, Bermejo, Lozano, Figueira, &
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Mateo, 2006). In Assaf flocks, artificial rearing with milk is commonly used either for
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avoiding transmission of diseases (e.g. Visna-Maedi) and to obtain a greater amount of milk,
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provided the market price of this last one is high enough. Moreover, through artificial
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lactation controlling milk intake and, to a certain extent, the length of the rearing period could
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be easier. It might be possible to get the maximal incomes from the sale of the lambs provided
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carcass and meat characteristics were not affected.
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There are several studies comparing performance and meat quality of naturally and artificially
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reared lambs of local breeds (Osorio et al., 2006). Despite this, there is not information about
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the rearing system on performance and meat quality of Assaf lambs.
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Therefore, the objective of this study was to evaluate the effect of sex and rearing system on
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growth and carcass and meat characteristics of Assaf milk fed lambs.
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Material and methods
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Experimental design and animal management
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Thirty-six Assaf lambs were included in a 2 x 3 factorial design in which the effects of sex
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and feeding system (naturally and artificially rearing at two different levels of intake) were
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studied in lambs from 2 days old to 10 kg live body weight. Naturally reared (NR) lambs (6
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males and 6 females) were raised exclusively on maternal milk from birth to slaughter and did
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not receive any kind of solid food. Throughout of the course of the experiment NR lambs
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were always kept with their dams. Dams were supplemented with hay and concentrate, and at
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second day postpartum were allowed to graze at pasture for four hours a day.
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Artificially reared lambs were removed from the ewes within 24-36 hours of birth and housed
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in individual pens. Twelve of them (AAR) (6 males and 6 females) were fed ad libitum twice
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daily (09:00 and 19:00 h) with a commercial reconstituted cow’s milk [18.5% dry matter
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(DM), 45 g of crude protein (CP)/kg and 47 g of crude fat (ether extract)/kg]. The other
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twelve lambs (RAR) (6 males and 6 females) were fed with the same reconstituted milk
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offered twice a day at 70% of the level intake of AAR group. Daily allowance of RAR group
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was adjusted three times a week, according to LBW and intake of AAR group. The milk
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replacer was prepared immediately before the distribution and supplemented with NaCl (0.5
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g/kg), Ca2PO4 (1 g/kg) and vitamins A (500 µg/g), D3 (7.5 µg/g) and E (600 µg/kg). Reconstituted
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milk replacer was offered in clean bottles, and lambs were trained to suck the milk replacer using
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polythene tubes and silicone teats. Milk refusals were weighed to determine the milk intake. All
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lambs were weighed at birth and three times a week throughout the experimental period.
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Slaughter procedure and non carcass weights
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When animals reached 10 kg live body weight, they were anaesthetised using sodium
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pentobarbitone and slaughtered by exsanguination from the jugular vein, eviscerated and
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skinned. The whole body of each lamb was dissected into carcass (which included thymus,
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testicles, kidneys and the kidney knob and channel fat). The weights of the empty digestive
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tract and the digestive (omental and mesenteric) fat and kidney knob carcass fat depots were
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recorded.
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Carcass characteristics
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Carcasses were chilled at 4 ºC during 24 h in a conventional chill cooler and then, cold
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carcasses weight (CCW) was recorded (CCW). Chilling losses were estimated as the
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difference between cold and hot carcass weight relative to the hot carcass weight. The killing
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out percentage was calculated as the CCW expressed as a proportion of the slaughter weight.
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The following carcass measurements described by Colomer-Rocher, Delfa, and Sierra Alfranca,
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1988) were assessed to determine carcass morphology: buttock perimeter (B), buttock length (G),
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carcass external length (K) and pelvic limb length (F). The index for carcass conformation (cold
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carcass weight/carcass external length) was calculated. Right half carcasses containing the tails
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were minced, mixed and homogenized in a commercial blender, and samples were taken and
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stored at -30 ºC, then lyophilized (FTS-Lyostar, United States) for chemical composition
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analysis.
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Meat characteristics
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Meat characteristics were evaluated in the longissimus thoracis and longissimus lumborum
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muscles of the left carcass. At the 6th rib, the muscle pH was measured, using a Metrohm®
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pH meter, equipped with a penetrating electrode. Immediately after 1 hour blooming,
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instrumental color CIE L* (lightness), a* (redness) and b* (yellowness) (CIE, 1986) readings
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were taken in the longissimus thoracis muscle at 13th rib using a spectrophotometer (Minolta
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Croma Meter 2002, Germany). Eye muscle area was measured in the 6th rib position by
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outlining on a transparency and then using a plannimeter (Areameter MK2, Holland).
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The longissimus lumborum muscle was minced, frozen (–20 ºC), lyophilized (FTS-Lyostar,
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United States) and analyzed for chemical composition. A subsample from longissimus
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thoracis muscle was taken to determine the water holding capacity. Filter paper press
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procedure described by Grau and Hamm (1953) and modified by Sierra (1973) was used to
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determine pressure losses. The remaining portion was vacuum-packed and frozen (–20º C) for
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subsequent measurements of cooking losses and instrumental hardness. Longissimus thoracis
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muscles were cooked in a water bath until internal temperature reached 70ºC. Cooking loss
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was expressed as a proportion of the initial weight. Longissimus thoracis cooked samples (10
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x 10 x 20 mm prismatic portions) were used to determine Warner-Bratzler shear force
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(Texture Analyzer TA.XT2, Great Britain).
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Chemical analysis
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The procedures outlined by the AOAC (1999) were used to determine dry matter (DM,
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method ID 950.46), ash (method ID 920.153), Kjeldahl N (CP, method ID 981.10) and crude
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fat content (method ID 960.39) of the carcass and longissimus lumborum samples.
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Statistical analysis
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The data were subject to an analysis of variance according to a factorial design to determine
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the effect of sex and rearing system on animal performance, carcass and meat characteristics.
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When the F-test for rearing system or sexrearing system effects were significant (P < 0.05),
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multiple comparisons among means were examined by the least significance difference test.
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All analyses were performed using the GLM procedure of the Statistical Analysis Systems
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(SAS, 1999).
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Results
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Intake and growth performance
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Mean values of dry matter intake, daily body weight gain (BWG) and feed conversion
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efficiency are shown in Table 1. Neither growth rate nor feed conversion efficiency were
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affected (p>0.05) by sex. Regarding the effect of feeding treatments, daily body weight gain
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of naturally reared lambs was consistently (p<0.05) higher than that of artificially reared
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lambs. As expected, AAR lambs showed also a higher growth rate and lower feed conversion
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efficiency than those of restricted group (RAR) (p<0.05). There was no significant (p>0.05)
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interaction between rearing system and sex for any of these parameters.
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(Table 1 near here)
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Non-carcass and carcass characteristics
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Neither dietary treatment nor sex affected non-carcass weight (see table 2). Sex did not affect
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the weight of the empty digestive tract, but significant differences in the weight of empty
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digestive tract were observed between rearing systems (p<0.05). The empty digestive tract
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was 19% greater in RAR than in NR lambs (p<0.05). Digestive tract and fat depots were
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affected by rearing system. NR lambs showed greater omental and lower mesenteric content
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than RAR lambs (p<0.05). As regards the sex effect, males presented lower total digestive fat
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values than females (p<0.05).
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(Table 2 near here)
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Carcass weight and killing out percentage were not significantly (P>0.05) affected. Chilling
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losses were significantly (p<0.05) greater in RAR lambs than in NR or AAR lambs. The RAR
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lambs showed significantly longer carcasses (p<0.001) than NR and AAR lambs, while pelvic
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limbs length where higher for RAR than for NR lambs (p<0.05). Consequently, NR carcass
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compactness index was greater than in artificially reared lambs (p<0.01). There were not
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significant differences in linear measurements due to sex effect (p>0.10).
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With the exception of ether extract content of the carcass (26% higher for females than for
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males, p<0.01), there were not significant differences in chemical composition of the carcass
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composition due to sex effect (p>0.10). There were differences in carcass fat content between
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feeding systems, RAR lambs showed lower values than NR lambs (p<0.05).
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Meat characteristics
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As shown in Table 3, there were not significant differences due to feeding system in the
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longissimus thoracis pH after 24 hours postmortem, colour parameters, cooking losses and
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chemical composition (p>0.05). Pressure losses showed 15% greater values in artificially
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(AAR and RAR) than in NR lambs. Sex did not affect longissimus thoracis and longissimus
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lumborum characteristics, with the exception of water (p<0.05) and ether extract contents
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(p<0.001). Male lambs showed significantly 45% lower values in ether extract content than
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female lambs.
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(Table 3 near here)
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Discussion
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Effect of sex
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There is convincing evidence that growth rate, feed conversion efficiency, body composition
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and carcass and meat quality can be affected by sex, although sexual dimorphism appears at
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different body weight depending on the sheep breed.
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Greater fat content, either in digestive depots or in the carcass and meat, in females than in
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males observed in the present experiment could be supported by the concept that females
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mature faster and fatten earlier than males (Butterfield, 1988). Similar results have been found
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by Miguel, Huidobro, Díaz, Velasco, Lauzurica, Pérez et al. (2003) in Manchega and by
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Horcada, Beriain, Purroy, Lizaso, and Chasco (1998) in Lacha suckling lambs. These results
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confirm that, in Assaf breed, differences due to sex can be also evident at a very low body
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weight, although adult size is greater for Assaf than other native Spanish breeds.
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The results of meat chemical composition found in this study are in agreement with those of
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Hoffman, Muller, Cloete, and Schmidt (2003) who reported that water is mainly located in
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muscle and its content decrease as intramuscular fat proportion increase. Several meat
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characteristics such as hardness or colour parameters are related to intramuscular fat content
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(Fahmy, Boucher, Poste, Grégoire, Butler, & Comeau, 1992). Nevertheless, the lack of
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differences in all of these parameters suggests that differences due to sex in adipose growth
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observed in the present study were quantitatively irrelevant on meat characteristics. Other
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studies on Spanish sheep breeds, including the Churra (Manso, Mantecón, & Castro, 1998)
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and Manchega (Cañeque, Lauzurica, Guía, & López, 1990; Vergara & Gallego, 1999)
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reported non differences between sexes.
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Effect of rearing system
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Spanish dairy sheep flocks are usually conceived to produce lambs and milk. Feed intake of
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suckling lambs during the first weeks of life depends on milk production of their dams and the
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suckling regime. Thus, milk intake and, consequently, growth rate increase as milk yield and
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the suckling frequency increase and it is not surprising that for low yielding dairy ewes lamb
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performance may be worse for naturally than artificially reared lambs, if those receive milk-
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replacer several times a day. In the present study, AAR lambs received milk-replacer only
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twice a day, whereas NR lambs remained continuously with their mothers, which are high
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yielding dairy ewes (Ugarte et al., 2001). Therefore, the differences reported in average daily
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gain between NR and AAR lambs probably were associated with differences in the milk
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intake.
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Native dairy Spanish sheep breeds, such as Churra, Manchega, Lacha or Castellana, are much
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less productive than Assaf or Awassi ewes (Ugarte et al., 2001). Thus, it is not surprising that
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average daily gain values for NR Assaf lambs were similar to those reported by Al Jassim,
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Aziz, Zorah, and Black (1999) for Awassi suckling lambs and greater than those reported for
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naturally reared lambs of different Spanish breeds (Peláez, 1979; De la Fuente, Tejón, Rey,
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Thos, & López-Bote, 1998; Beriain et al., 2000).
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On the other hand, it is noteworthy to point out that intake, growth rate and feed conversion
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efficiency values of AAR lambs obtained in this study were similar to those obtained by
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Peláez (1979) in Churra lambs also fed with cow’s reconstituted milk twice a day. This
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suggests that, when they are fed in the same conditions, performance of Assaf lambs is similar
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to that of Churra lambs. Other authors reported similar growth rates for artificially or
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naturally reared lambs, although this fact depends on breed and feeding regime (Napolitano et
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al., 2002a).
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The regulation of the digestive tract growth is complex as it is affected by metabolic,
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chemical and physical factors, and most of the development occurs during the fetal and
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perinatal period (Baldwin et al., 2004). Regarding milk fed lambs, it has been suggested that
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ruminal and intestinal mass development is usually faster for lambs reared under natural
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conditions (Kaiser, 1976; De la Fuente et al., 1998). Our findings do not agree with those,
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since digestive tract weight was greater for artificially than for naturally reared lambs.
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However, feeding frequency or meal size could modulate gastrointestinal development
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(Kristensen, Sehested, Jensen, & Vestergaard, 2007), which could explain the differences
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between naturally and artificially reared lambs as average meal size could be expected to be
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greater for the latter. On the other hand, the effect of the feeding system on omental and
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mesenteric fat deposition followed different patterns. Thus, the greatest mesenteric fat
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deposition occurred with the artificially reared lambs, while naturally reared lambs showed
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the greater omental fat content. Although differences in the development of the different
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sections of the digestive tract could explain those effects, this statement can not be confirmed
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since those data were not recorded in the present study.
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In agreement with Napolitano et al. (2002a) there were not differences in killing out
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percentage between naturally and artificially reared lambs. However, the higher chilling
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losses observed in RAR lambs might be attributed to a lower carcass fat content compared
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with NR and AAR lambs. It is well known that fat content has an effect on chilling losses
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since fat act slows down moisture evaporation (Johnson, Hunt, Allen, Kastner, Danler, &
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Schrock, 1988).
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The 70% milk restriction level of RAR compared with AAR lambs resulted in a lower carcass
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fat deposition, yet not in a muscle deposition as was shown by the similar values of carcass
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crude protein content. This differences points out that RAR raised animals, had energy and
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protein supply enough to reach the maximum protein deposition but not for achieving the
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same fat accretion, as was suggested by Webster (1986) who reported that fat deposition is
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directly related to energy:protein intake rate.
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The rearing system affected the pressure losses of water from the longissimus thoracis
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muscle, the other meat characteristics being unaffected. Generally restricted feeding animals
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could lower water holding capacity as a result of a lower fat content (Hornick, Van Eenaeme,
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Clinquart, Diez, & Istasse, 1998). In our case, the differences between artificially reared
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lambs were not significant, whereas differences in pressures losses were found between
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artificial and naturally reared lambs. Naturally reared lambs could be more sensitive to pre-
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slaughter stress than artificially reared lambs as the latter were individually accommodated
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and used to management. Pre-slaughter stress could reduce muscle glycogen reserves and as a
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consequence result in a higher initial pH and lower pressure losses. Results of the present
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study showed that pH values at 24 hours were similar for both, naturally and artificially reared
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groups. However, as was previously reported (Fernandez, Monin, Culioli, Legrand, &
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Quilichini, 1996), differences in the pH decline during the first hours from slaughter may
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affect water holding capacity of meat. Likewise, differences in water holding capacity when
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lambs have different growth pattern may have been the net effect of a number of factors,
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including differences in the nature of the collagen (Purchas, Burnham, & Morris, 2002) that
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were not measured directly in this study.
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The results of this study show that the employment of artificial rearing systems permitted
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carcass characteristics similar to those observed in naturally raised lambs, and similar to the
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values found in other autochthonous breeds, when milk replacer is given ad libitum twice a
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day. A milk restricted supply reduced carcass fatness and compactness. Except for water
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holding capacity, no differences were found in the meat characteristics analyzed.
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References
266
AL Jassim, R.A.M., Aziz, D.I., Zorah, K., Black, J.L. 1999. Effect of concentrate feeding on milk
267
yield and body-weight change of Awassi ewes and the growth of their lambs. Animal Science, 69,
268
441-446.
269
AOAC (1999). Official methods of analysis of the Association of Official Analytical Chemist (16th
270
Ed.). AOAC, International, Gaithersburg (United States).
271
Baldwin, R. L., McLeod, R., Klotz, J. L., & Heitmann, R. N. (2004). Rumen development,
272
intestinal growth and hepatic metabolism in the pre- and postweaning ruminant. Journal of Dairy
273
Science, 87, 55–65
274
Beriaín, M.J., Horcada, A., Purroy, A., Lizaso, G., Chasco, J., & Mendizabal, J.A. (2000).
275
Characteristics of Lacha and Rasa Aragonesa lambs slaughtered at three live weights. Journal of
276
Animal Science, 78, 3070-3077.
277
Butterfield, R.M. (1988). New concepts of sheep growth. Department of Veterinary Anatomy
278
University of Sydney (Australia).
279
Cañeque Martínez, V., Lauzurica Gómez, S., Guía, E., & López, E. (1990). Empleo de distintas
280
cantidades de leche en lactancia artificial de corderos de raza Manchega. ITEA, 86, 164-171.
281
CIE (1986). Colorimetry, 2nd Edn. CIE Publications 15.2 Commission Internationale de
282
l'Eclairage, Viena (Austria).
283
Colomer-Rocher, F., Delfa, R., & Sierra Alfranca, I. (1988). Metodo normalizado para el estudio de
284
los caracteres cuantitativos y cualitativos de las canales ovinas producidas en el area Mediterránea,
285
según los sistemas de producción (1). Cuadernos del INIA, 17, 19-41.
286
De la Fuente, J., Tejón, D., Rey, A., Thos, J., & López-Bote, C. (1998). Effect of rearing system on
287
growth, body composition and development of digestive system in young lambs. Journal of Animal
288
Physiology and Animal Nutrition, 78, 75-83.
289
Fahmy, M.H., Boucher, J.M., Poste, L.M., Grégoire, R., Butler, G., & Comeau, J.E. (1992). Feed
290
efficiency, carcass characteristics and sensory quality of lambs, with or without prolific ancestry,
291
fed diets with different protein supplements. Journal of Animal Science, 70, 1365-1374.
13
292
Fernandez, X., Monin, G., Culioli, J., Legrand, I., & Quilichini, Y. (1996). Effect of duration of
293
feed withdrawal and transportation time on muscle characteristics and quality in Friesian-Holstein
294
calves. Journal of Animal Science, 74, 1576–1583
295
Grau, R., & Hamm, R. (1953). Eine einfache methode zur bestimmung der wasserbindung im
296
muskel. Naturwissenschafen, 40, 29-30.
297
Hoffman, L.C., Muller, M., Cloete, S.W.P., & Schmidt, D. (2003). Comparison of six crossbred
298
lambs types:sensory, physical and nutritional meat quality characteristics. Meat Science, 65, 1265-
299
1274.
300
Horcada, A., Beriain, M.J., Purroy, A., Lizaso, G., & Chasco, J. (1998). Effect of sex on meat
301
quality of Spanish lamb breeds (Lacha and Rasa Aragonesa). Animal Science, 67, 541-547.
302
Hornick, J.L., Van Eenaeme, C., Clinquart, A., Diez, M., & Istasse, L. (1998). Different periods of
303
feed restriction before compensatory growth in Belgian Blue bulls: I. Animal performance, nitrogen
304
balance, meat characteristics, and fat composition. Journal of Animal Science, 76, 249-259.
305
Johnson, R. D., Hunt, M. C., Allen, D. M., Kastner, C. L. Danler, R. J. & Schrock, C. C. (1988).
306
Moisture uptake during washing and spray chilling of holstein and beef-type steer carcasses.
307
Journal Animal Science, 66, 2180-2184.
308
Kaiser, A.G. (1976). The effects of milk feeding on the pre- and post-weaning growth of calves, and
309
on stomach development at weaning. Journal of Agriculture Science, Cambridge, 87, 357-363.
310
Kristensen, N. B., Sehested, J., Jensen, S. K., & Vestergaard, M. (2007). Effect of milk allowance
311
on concentrate intake, ruminal environment, and ruminal development in milk-fed holstein Calves.
312
Journal of Dairy Science, 90, 4346-4355.
313
Macit, M., Esenbuga, N., & Karaoglu, M. (2002). Growth performance and carcass characteristics
314
of Awassi, Morkaraman and Tushin lamb grazed on pasture and supported with concentrate. Small
315
Ruminant Research, 44, 241-246.
316
Manso, T., Mantecón, A.R., & Castro, T. (1998). Rendimiento a la canal, quinto cuarto y despiece
317
de corderos de raza Churra sometidos a distintas estrategias de alimentación. Archivos de
318
Zootecnia, 47, 73-84.
319
Miguel, E., Huidobro, F.R., Díaz, M.T., Velasco, S., Lauzurica, S., Pérez, C., Onega, E., Blázquez,
320
B., & Cañeque, V. (2003). Methods of carcass classification based on subjetive assessments of
14
321
carcass fatness and of carcass conformation: effect of sex on the prediction of tissue composition in
322
carcasses of sucking lambs. Animal Science, 77, 383-393.
323
Napolitano, F., Braghieri, A., Cifuni, G.F., Pacelli, C., Girolami, A. (2002a). Behaviour and meat
324
production of organically farmed unweaned lambs. Small Ruminant Research, 43, 179-184.
325
Napolitano, F., Cifuni, G.F., Pacelli, C., Riviezzi, A.M., & Girolami, A. (2002b). Effect of artificial
326
rearing on lamb welfare and meat quality. Meat Science, 60, 307-315.
327
Osorio, M.T., Zumalacárregui, J.M., Bermejo, B., Lozano, A., Figueira, A.C., & Mateo, J. (2006).
328
Effect of ewe's milk versus milk-replacer rearing on mineral composition of suckling lamb meat
329
and liver. Small Ruminant Research, 68, 296-302.
330
Peláez, R. (1979). Digestibilidad, utilización de la energía y balances de nitrógeno en corderos de
331
raza Churra, criados artificialmente a base de leche de oveja, leche de vaca y sustitutivos lácteos.
332
PhD Thesis. Universidad de León. Facultad de Veterinaria. León, Spain.
333
Purchas, R. W., Burnham, D. L., & Morris, S. T. (2002). Effects of growth potential and growth
334
path on tenderness of beef longissimus muscle from bulls and steers. Journal of Animal Science, 80,
335
3211–3221.
336
Santos-Silva, J., Mendes, I.A., & Bessa, R.J.B. (2002). The effect of genotype, feeding system and
337
the slaughter weight on the quality of light lambs. 1. Growth, carcass composition and meat quality.
338
Livestock Production Science, 76, 17-25.
339
Sañudo, C., Campo, M.M., Sierra, I., María, G.A., Olleta, J.L., & Santolaria, P. (1997). Breed effect
340
on carcasse and meat quality of suckling lambs. Meat Science, 46, 357-365.
341
SAS INST. INC. (1999). SAS/STAT®. User's Guide (Version 8) .SAS Publishing, Cary, NC
342
(United States).
343
Sierra, I., 1973. Producción de cordero joven y pesado de la raza Rasa Aragonesa. Instituto de
344
Economía y Producciones Ganaderas del Ebro, 18, pp. 1-28.
345
Titi, H.H., Dmour R.O., & Abdullah, A.Y. (2007). Growth performance and carcass characteristics
346
of Awassi lambs and Shami goat kids fed yeast culture in their finishing diet. Animal Feed Science
347
and Technology (In press).
348
Ugarte, E., Ruiz, R., Gabiña, D., & Beltrán de Heredia, I. (2001). Impact of high-yielding foreign
349
breeds on the Spanish dairy sheep industry. Livestock Production Science, 71, 3-10.
15
350
Vergara, H., & Gallego, L. (1999). Effect of type of suckling and length of lactation period on
351
carcass and meat quality in intensive lamb production systems. Meat Science, 53, 211-215.
352
Webster, A.J.F. (1986). Factors affecting the body composition of growing and adult animals.
353
Proceedings of the Nutrition Society, 45, 45-53.
354
355
356
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