Carcass and Meat Quality of Assaf Milk Fed Lambs: Effect of Rearing System and Sex

1Carcass and meat quality of Assaf milk fed lambs: effect of rearing

2 system and sex

3 *Rodríguez, A.B., Landa, R., Bodas, R., Prieto, N., Mantecón, A.R.,

4 Giráldez, F.J.

5 Estación Agrícola Experimental (CSIC). Finca Marzanas, 24346-Grulleros, León (Spain)

7* Corresponding author: Tel. (34) 987 31 71 56; Fax (34) 987 31 71 61

8E-mail address: [email protected]

1 1 9Abstract

10The effect of sex and rearing system on growth and carcass and meat characteristics of milk-

11fed Assaf lambs was studied. Thirty-six lambs, 18 males and 18 females were used. Twelve

12lambs remained with their mothers throughout the experiment (NR). Within 24-36 hours of

13birth, the rest were housed individually and fed twice a day ad libitum (AAR) or at 70% of ad

14libitum consumption (RAR) with reconstituted cow milk. Sex did not affect animal

15performance, yet females showed higher carcass and non carcass fat deposits. NR lambs

16showed greater BWG than AAR fed lambs, and AAR, higher than the RAR. Differences

17between naturally and artificially reared lambs in CCW and killing out percentage were not

18significant. Empty digestive tract and mesenteric fat weights were greater for RAR than NR

19lambs, with the AAR lambs demonstrating intermediate values; conversely, omental fat was

20greater in NR lambs. Carcass ether extract content was greater for NR lambs, possibly due to

21the greater growth. Use of ad libitum cow’s milk substitute in suckling lambs twice a day

22resulted in less body weight gain but similar killing out percentages than naturally raised

23lambs. A 70% restricted supply increased the days in suckling and reduced carcass fatness and

24compactness. Except for water loss, which was less in NR than artificially fed lambs, no

25differences were found in meat characteristics.

26Keywords: Lamb; naturally; artificially milk feeding system; growth, carcass, non carcass,

27meat quality.

28Introduction

29Traditionally, in the Mediterranean countries of EU, most dairy sheep systems produce lambs

30aimed at 10 kg live weight. This type of lamb is a very valuable product due to its appreciated

31organoleptic qualities. In Spain during many decades, Churra and Castellana were the most

32important dairy breeds and hence most of milk fed lambs were from these breeds.

33Nevertheless, in the last twenty years the population of local dairy breeds has greatly

2 2 34decreased whereas the population of foreign breeds, such as Awassi or Assaf, has increased

35(Ugarte, Ruiz, Gabiña, & Beltrán de Heredia, 2001). Currently, the Assaf breed is becoming

36the most important dairy sheep breed in a number of Spanish regions and, at this moment, its

37population is estimated to be around 800,000 animals (Ugarte et al., 2001). In consequence of

38this, lamb meat production of this foreign breed has significantly increased.

39It is well known that ewe genotype could have a significant effect on lamb performance and

40carcass and meat quality (Sañudo, Campo, Sierra, María, Olleta, & Santolaria, 1997; Beriaín,

41Horcada, Purroy, Lizaso, Chasco, & Mendizabal, 2000; Santos-Silva, Mendes, & Bessa,

422002). Different authors have analysed the growth and carcass and meat characteristics of fat-

43tailed lambs, and the Awassi is one of the most studied (Macit, Esenbuga, & Karaoglu, 2002;

44Titi, Dmour, & Abdullah, 2007).

45Likewise, comparative studies of Awassi and Spanish dairy breeds have been carried out and

46differences in parameters such as killing out percentage, carcass conformation, meat colour or

47cooking losses have been reported (Sañudo et al., 1997). Nevertheless, to the best of our

48knowledge, there are not many published data on performance and carcass and meat quality of

49Assaf lambs.

50In addition to genotype, animal performance and meat quality can also be affected by rearing

51system (Napolitano, Braghieri, Cifuni, Pacelli, & Girolami, 2002a; Napolitano, Cifuni,

52Pacelli, Riviezzi, & Girolami, 2002b; Osorio, Zumalacárregui, Bermejo, Lozano, Figueira, &

53Mateo, 2006). In Assaf flocks, artificial rearing with milk is commonly used either for

54avoiding transmission of diseases (e.g. Visna-Maedi) and to obtain a greater amount of milk,

55provided the market price of this last one is high enough. Moreover, through artificial

56lactation controlling milk intake and, to a certain extent, the length of the rearing period could

57be easier. It might be possible to get the maximal incomes from the sale of the lambs provided

58carcass and meat characteristics were not affected.

3 3 59There are several studies comparing performance and meat quality of naturally and artificially

60reared lambs of local breeds (Osorio et al., 2006). Despite this, there is not information about

61the rearing system on performance and meat quality of Assaf lambs.

62Therefore, the objective of this study was to evaluate the effect of sex and rearing system on

63growth and carcass and meat characteristics of Assaf milk fed lambs.

64Material and methods

65Experimental design and animal management

66Thirty-six Assaf lambs were included in a 2 x 3 factorial design in which the effects of sex

67and feeding system (naturally and artificially rearing at two different levels of intake) were

68studied in lambs from 2 days old to 10 kg live body weight. Naturally reared (NR) lambs (6

69males and 6 females) were raised exclusively on maternal milk from birth to slaughter and did

70not receive any kind of solid food. Throughout of the course of the experiment NR lambs

71were always kept with their dams. Dams were supplemented with hay and concentrate, and at

72second day postpartum were allowed to graze at pasture for four hours a day.

73Artificially reared lambs were removed from the ewes within 24-36 hours of birth and housed

74in individual pens. Twelve of them (AAR) (6 males and 6 females) were fed ad libitum twice

75daily (09:00 and 19:00 h) with a commercial reconstituted cow’s milk [18.5% dry matter

76(DM), 45 g of crude protein (CP)/kg and 47 g of crude fat (ether extract)/kg]. The other

77twelve lambs (RAR) (6 males and 6 females) were fed with the same reconstituted milk

78offered twice a day at 70% of the level intake of AAR group. Daily allowance of RAR group

79was adjusted three times a week, according to LBW and intake of AAR group. The milk

80replacer was prepared immediately before the distribution and supplemented with NaCl (0.5

81g/kg), Ca2PO4 (1 g/kg) and vitamins A (500 µg/g), D3 (7.5 µg/g) and E (600 µg/kg). Reconstituted

82milk replacer was offered in clean bottles, and lambs were trained to suck the milk replacer using

4 4 83polythene tubes and silicone teats. Milk refusals were weighed to determine the milk intake. All

84lambs were weighed at birth and three times a week throughout the experimental period.

85Slaughter procedure and non carcass weights

86When animals reached 10 kg live body weight, they were anaesthetised using sodium

87pentobarbitone and slaughtered by exsanguination from the jugular vein, eviscerated and

88skinned. The whole body of each lamb was dissected into carcass (which included thymus,

89testicles, kidneys and the kidney knob and channel fat). The weights of the empty digestive

90tract and the digestive (omental and mesenteric) fat and kidney knob carcass fat depots were

91recorded.

92Carcass characteristics

93Carcasses were chilled at 4 ºC during 24 h in a conventional chill cooler and then, cold

94carcasses weight (CCW) was recorded (CCW). Chilling losses were estimated as the

95difference between cold and hot carcass weight relative to the hot carcass weight. The killing

96out percentage was calculated as the CCW expressed as a proportion of the slaughter weight.

97The following carcass measurements described by Colomer-Rocher, Delfa, and Sierra Alfranca,

981988) were assessed to determine carcass morphology: buttock perimeter (B), buttock length (G),

99carcass external length (K) and pelvic limb length (F). The index for carcass conformation (cold

100carcass weight/carcass external length) was calculated. Right half carcasses containing the tails

101were minced, mixed and homogenized in a commercial blender, and samples were taken and

102stored at -30 ºC, then lyophilized (FTS-Lyostar, United States) for chemical composition

103analysis.

104Meat characteristics

105Meat characteristics were evaluated in the longissimus thoracis and longissimus lumborum

106muscles of the left carcass. At the 6th rib, the muscle pH was measured, using a Metrohm® pH

107meter, equipped with a penetrating electrode. Immediately after 1 hour blooming,

5 5 108instrumental color CIE L* (lightness), a* (redness) and b* (yellowness) (CIE, 1986) readings

109were taken in the longissimus thoracis muscle at 13th rib using a spectrophotometer (Minolta

110Croma Meter 2002, Germany). Eye muscle area was measured in the 6th rib position by

111outlining on a transparency and then using a plannimeter (Areameter MK2, Holland).

112The longissimus lumborum muscle was minced, frozen (–20 ºC), lyophilized (FTS-Lyostar,

113United States) and analyzed for chemical composition. A subsample from longissimus

114thoracis muscle was taken to determine the water holding capacity. Filter paper press

115procedure described by Grau and Hamm (1953) and modified by Sierra (1973) was used to

116determine pressure losses. The remaining portion was vacuum-packed and frozen (–20º C) for

117subsequent measurements of cooking losses and instrumental hardness. Longissimus thoracis

118muscles were cooked in a water bath until internal temperature reached 70ºC. Cooking loss

119was expressed as a proportion of the initial weight. Longissimus thoracis cooked samples (10

120x 10 x 20 mm prismatic portions) were used to determine Warner-Bratzler shear force

121(Texture Analyzer TA.XT2, Great Britain).

122Chemical analysis

123The procedures outlined by the AOAC (1999) were used to determine dry matter (DM,

124method ID 950.46), ash (method ID 920.153), Kjeldahl N (CP, method ID 981.10) and crude

125fat content (method ID 960.39) of the carcass and longissimus lumborum samples.

126Statistical analysis

127The data were subject to an analysis of variance according to a factorial design to determine

128the effect of sex and rearing system on animal performance, carcass and meat characteristics.

129When the F-test for rearing system or sexrearing system effects were significant (P < 0.05),

130multiple comparisons among means were examined by the least significance difference test.

131All analyses were performed using the GLM procedure of the Statistical Analysis Systems

132(SAS, 1999).

6 6 133Results

134Intake and growth performance

135Mean values of dry matter intake, daily body weight gain (BWG) and feed conversion

136efficiency are shown in Table 1. Neither growth rate nor feed conversion efficiency were

137affected (p>0.05) by sex. Regarding the effect of feeding treatments, daily body weight gain

138of naturally reared lambs was consistently (p<0.05) higher than that of artificially reared

139lambs. As expected, AAR lambs showed also a higher growth rate and lower feed conversion

140efficiency than those of restricted group (RAR) (p<0.05). There was no significant (p>0.05)

141interaction between rearing system and sex for any of these parameters.

142 (Table 1 near here)

143Non-carcass and carcass characteristics

144Neither dietary treatment nor sex affected non-carcass weight (see table 2). Sex did not affect

145the weight of the empty digestive tract, but significant differences in the weight of empty

146digestive tract were observed between rearing systems (p<0.05). The empty digestive tract

147was 19% greater in RAR than in NR lambs (p<0.05). Digestive tract and fat depots were

148affected by rearing system. NR lambs showed greater omental and lower mesenteric content

149than RAR lambs (p<0.05). As regards the sex effect, males presented lower total digestive fat

150values than females (p<0.05).

152Carcass weight and killing out percentage were not significantly (P>0.05) affected. Chilling

153losses were significantly (p<0.05) greater in RAR lambs than in NR or AAR lambs. The RAR

154lambs showed significantly longer carcasses (p<0.001) than NR and AAR lambs, while pelvic

155limbs length where higher for RAR than for NR lambs (p<0.05). Consequently, NR carcass

156compactness index was greater than in artificially reared lambs (p<0.01). There were not

157significant differences in linear measurements due to sex effect (p>0.10).

7 7 158With the exception of ether extract content of the carcass (26% higher for females than for

159males, p<0.01), there were not significant differences in chemical composition of the carcass

160composition due to sex effect (p>0.10). There were differences in carcass fat content between

161feeding systems, RAR lambs showed lower values than NR lambs (p<0.05).

162Meat characteristics

163As shown in Table 3, there were not significant differences due to feeding system in the

164longissimus thoracis pH after 24 hours postmortem, colour parameters, cooking losses and

165chemical composition (p>0.05). Pressure losses showed 15% greater values in artificially

166(AAR and RAR) than in NR lambs. Sex did not affect longissimus thoracis and longissimus

167lumborum characteristics, with the exception of water (p<0.05) and ether extract contents

168(p<0.001). Male lambs showed significantly 45% lower values in ether extract content than

169female lambs.

171Discussion

172Effect of sex

173There is convincing evidence that growth rate, feed conversion efficiency, body composition

174and carcass and meat quality can be affected by sex, although sexual dimorphism appears at

175different body weight depending on the sheep breed.

176Greater fat content, either in digestive depots or in the carcass and meat, in females than in

177males observed in the present experiment could be supported by the concept that females

178mature faster and fatten earlier than males (Butterfield, 1988). Similar results have been found

179by Miguel, Huidobro, Díaz, Velasco, Lauzurica, Pérez et al. (2003) in Manchega and by

180Horcada, Beriain, Purroy, Lizaso, and Chasco (1998) in Lacha suckling lambs. These results

181confirm that, in Assaf breed, differences due to sex can be also evident at a very low body

182weight, although adult size is greater for Assaf than other native Spanish breeds.

8 8 183The results of meat chemical composition found in this study are in agreement with those of

184Hoffman, Muller, Cloete, and Schmidt (2003) who reported that water is mainly located in

185muscle and its content decrease as intramuscular fat proportion increase. Several meat

186characteristics such as hardness or colour parameters are related to intramuscular fat content

187(Fahmy, Boucher, Poste, Grégoire, Butler, & Comeau, 1992). Nevertheless, the lack of

188differences in all of these parameters suggests that differences due to sex in adipose growth

189observed in the present study were quantitatively irrelevant on meat characteristics. Other

190studies on Spanish sheep breeds, including the Churra (Manso, Mantecón, & Castro, 1998)

191and Manchega (Cañeque, Lauzurica, Guía, & López, 1990; Vergara & Gallego, 1999)

192reported non differences between sexes.

193Effect of rearing system

194Spanish dairy sheep flocks are usually conceived to produce lambs and milk. Feed intake of

195suckling lambs during the first weeks of life depends on milk production of their dams and the

196suckling regime. Thus, milk intake and, consequently, growth rate increase as milk yield and

197the suckling frequency increase and it is not surprising that for low yielding dairy ewes lamb

198performance may be worse for naturally than artificially reared lambs, if those receive milk-

199replacer several times a day. In the present study, AAR lambs received milk-replacer only

200twice a day, whereas NR lambs remained continuously with their mothers, which are high

201yielding dairy ewes (Ugarte et al., 2001). Therefore, the differences reported in average daily

202gain between NR and AAR lambs probably were associated with differences in the milk

203intake.

204Native dairy Spanish sheep breeds, such as Churra, Manchega, Lacha or Castellana, are much

205less productive than Assaf or Awassi ewes (Ugarte et al., 2001). Thus, it is not surprising that

206average daily gain values for NR Assaf lambs were similar to those reported by Al Jassim,

207Aziz, Zorah, and Black (1999) for Awassi suckling lambs and greater than those reported for

9 9 208naturally reared lambs of different Spanish breeds (Peláez, 1979; De la Fuente, Tejón, Rey,

209Thos, & López-Bote, 1998; Beriain et al., 2000).

210On the other hand, it is noteworthy to point out that intake, growth rate and feed conversion

211efficiency values of AAR lambs obtained in this study were similar to those obtained by

212Peláez (1979) in Churra lambs also fed with cow’s reconstituted milk twice a day. This

213suggests that, when they are fed in the same conditions, performance of Assaf lambs is similar

214to that of Churra lambs. Other authors reported similar growth rates for artificially or

215naturally reared lambs, although this fact depends on breed and feeding regime (Napolitano et

216al., 2002a).

217The regulation of the digestive tract growth is complex as it is affected by metabolic,

218chemical and physical factors, and most of the development occurs during the fetal and

219perinatal period (Baldwin et al., 2004). Regarding milk fed lambs, it has been suggested that

220ruminal and intestinal mass development is usually faster for lambs reared under natural

221conditions (Kaiser, 1976; De la Fuente et al., 1998). Our findings do not agree with those,

222since digestive tract weight was greater for artificially than for naturally reared lambs.

223However, feeding frequency or meal size could modulate gastrointestinal development

224(Kristensen, Sehested, Jensen, & Vestergaard, 2007), which could explain the differences

225between naturally and artificially reared lambs as average meal size could be expected to be

226greater for the latter. On the other hand, the effect of the feeding system on omental and

227mesenteric fat deposition followed different patterns. Thus, the greatest mesenteric fat

228deposition occurred with the artificially reared lambs, while naturally reared lambs showed

229the greater omental fat content. Although differences in the development of the different

230sections of the digestive tract could explain those effects, this statement can not be confirmed

231since those data were not recorded in the present study.

10 10 232In agreement with Napolitano et al. (2002a) there were not differences in killing out

233percentage between naturally and artificially reared lambs. However, the higher chilling

234losses observed in RAR lambs might be attributed to a lower carcass fat content compared

235with NR and AAR lambs. It is well known that fat content has an effect on chilling losses

236since fat act slows down moisture evaporation (Johnson, Hunt, Allen, Kastner, Danler, &

237Schrock, 1988).

238The 70% milk restriction level of RAR compared with AAR lambs resulted in a lower carcass

239fat deposition, yet not in a muscle deposition as was shown by the similar values of carcass

240crude protein content. This differences points out that RAR raised animals, had energy and

241protein supply enough to reach the maximum protein deposition but not for achieving the

242same fat accretion, as was suggested by Webster (1986) who reported that fat deposition is

243directly related to energy:protein intake rate.

244The rearing system affected the pressure losses of water from the longissimus thoracis

245muscle, the other meat characteristics being unaffected. Generally restricted feeding animals

246could lower water holding capacity as a result of a lower fat content (Hornick, Van Eenaeme,

247Clinquart, Diez, & Istasse, 1998). In our case, the differences between artificially reared

248lambs were not significant, whereas differences in pressures losses were found between

249artificial and naturally reared lambs. Naturally reared lambs could be more sensitive to pre-

250slaughter stress than artificially reared lambs as the latter were individually accommodated

251and used to management. Pre-slaughter stress could reduce muscle glycogen reserves and as a

252consequence result in a higher initial pH and lower pressure losses. Results of the present

253study showed that pH values at 24 hours were similar for both, naturally and artificially reared

254groups. However, as was previously reported (Fernandez, Monin, Culioli, Legrand, &

255Quilichini, 1996), differences in the pH decline during the first hours from slaughter may

256affect water holding capacity of meat. Likewise, differences in water holding capacity when

11 11 257lambs have different growth pattern may have been the net effect of a number of factors,

258including differences in the nature of the collagen (Purchas, Burnham, & Morris, 2002) that

259were not measured directly in this study.

260The results of this study show that the employment of artificial rearing systems permitted

261carcass characteristics similar to those observed in naturally raised lambs, and similar to the

262values found in other autochthonous breeds, when milk replacer is given ad libitum twice a

263day. A milk restricted supply reduced carcass fatness and compactness. Except for water

264holding capacity, no differences were found in the meat characteristics analyzed.

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