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)
6
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 sexrearing 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).
151 (Table 2 near here)
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.
170 (Table 3 near here)
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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