Carcass conformation and joints composition of Churra Galega Bragançana and crossbred lambs by Suffolk and Merino Precoce sire breeds

Carcasses of Churro Galego Bragançano purebred and Suffolk and Merino Precoce crossbred lambs reared under three different conventional production system of northeast of Portugal were evaluated. Carcasses of male lambs had larger muscle longissimus width (P < 0.05) and smaller subcutaneous fat thickness (P < 0.05) than the female lambs. Carcasses of crossbred lambs had higher (P < 0.05) compactness indices and leg and shoulder proportion than Bragançano purebred. Suffolk crossed had lower KKCF proportion (P < 0.05) than Bragançano and Merino crossbred lambs. Male lambs had higher (P < 0.05) muscle proportion in almost all carcass joints than the female lambs. It was concluded that Suffolk can be used as sire breed in Bragançano ewes to produce lambs with leaner and more compact carcasses and better fat distribution, which allows slaughtering at higher slaughter weight, specially in more intensive production systems. Female lambs should be slaughtered at lower carcass weight than male lambs in order to produce carcasses with the same fattening degree.

Palabras clave: ovino, cruzamiento, composición tisular, sistemas de producción, razas autóctonas.Kempster et al. (1987a) pointed out that matching crossbreeding with production systems is the key factor in lamb production improvement, in order to get leaner carcasses at optimum slaughter weight and age.Kirton et al. (1995a) supported that to produce heavy lambs with higher meat content, producers must use rams with large mature size as sire breeds and raise lambs to higher slaughter weights.Several authors (Croston et al., 1987;Kempster et al., 1987aKempster et al., , 1987b;;Teixeira et al., 1996;Ellis et al., 1997) have investigated the effect of crossbreeding in lamb carcass composition with promising results.Nevertheless little information is available on crossbreeding effect on carcass conformation measurements, carcass joints proportion and joints tissue composition.
The aim of this study was to evaluate the effect of two improved sire breeds, Suffolk and Merino Precoce, when mated to Churro Galego Bragançano local breed ewes, on carcass conformation measurements, joints proportion and in joints tissue composition in three different production systems in the northeast of Portugal.

Animals
This study was carried out on 151 male and female lambs from Churra Galega Bragançana local breed and from crossbred lambs by Suffolk and Merino Precoce sire breeds.The study was conducted on three different farms (location), selected to cover a range of management systems and climatic conditions of the northeast of Portugal.The location 1 was the Escola Superior Agrária de Bragança Experimental Farm, with an intensive management, producing lambs off grass, with conserved forages and with access to commercial concentrates.The commercial concentrate used had the following composition (g kg -1 ): crude protein 160, crude cellulose 90, ash 100, crude fat 40; and was offered ad libitum in a daily distribution until slaughter.The location 2 was an upland farm at 400 to 600 m high in the Montesinho Natural Park (Bragança), producing lambs off grass, some meadow hay, with a major period, in which stubbles are grazed.The location 3 was a hill farm above 800 m high in Montesinho Natural Park, producing lambs in extensive areas of hill grazing, with no feed supply, harsh weather during winter and grazing in oak areas of Quercus pyrenaica forest during summer.
In each location, two rams of each of the sire breeds, Churra Galega Bragançana, Suffolk and Merino Precoce, were used.The rams remained on the same farms throughout the 4 years of the experiment.The ewes from each location were assigned by random into three groups of 30 ewes for mating with the pairs of rams from each breed for a period of 30 days.
Lambs were reared under the conventional conditions of each farm and were slaughtered in order to attain the carcass weight between 8 to 14 kg, according to the conventional weight requirements for lamb consumption in Portugal (Alves and Teixeira, 1995).

Slaughter procedure and carcass measurements
Lambs were slaughter in the experimental slaughterhouse of the Escola Superior Agrária de Bragança, after 24 h fasting.Following slaughter, carcasses were weighed and cooled at 6ºC for 24 h.Carcass conformation measurements (Pálsson, 1939;Timon and Bichard, 1965) were taken on carcasses suspended in a gamble of constant width between legs (Fig. 1), described as follows: (i) carcass length (K, mm) -from the basis of the tail to the basis of the neck; (ii) leg  length (F, mm) -the smallest distance from the perineum to the interior face of the tarsal-metatarsal articular surface; (iii) width of the buttocks (G, mm) -the width measured using the measuring calliper at the level of the proximal edge of the patellae; (iv) width of chest (Wr, mm) -the greatest width of the chest, (v) width of the shoulders (S, mm) -the greatest width of the shoulders, (vi) circumference of thorax (U, mm)the circumference measured using a tape held horizontally around the thorax at the level of the caudal portion of the scapula; (vii) anterior circumference of buttocks (ACB, mm) -the circumference measured using a tape held horizontally around the buttocks at the level of the maximum width of the trochanter, (viii) posterior circumference of buttocks (PCB, mm) -the circumference measured using a tape held horizontally around the buttocks at the level of the caudal insertion.The leg compactness was evaluated by the relation between the width of the buttocks and leg length (G/F×100).The carcass compactness was evaluated by the relation between hot carcass weight (HCW) and carcass length (HCW/K, g cm -1 ) as proposed by Pálsson (1939).
Carcasses were halved through the centre of the vertebral column and the kidney knob and channel fat (KKCF) was removed and weighed.The left side was divided into eight standardised commercial joints: leg, chump, loin, ribs, anterior ribs, shoulder, breast and neck according to the commercial jointing and cutting system (Fig. 2) of Estação Zootécnica Nacional (Calheiros and Neves, 1968).Some tissue measurements (Pálsson, 1939;Timon and Bichard, 1965) were taken on the surface of muscle longissimus at 12 th -13 th ribs level, with a metal ruler (Fig. 3), as follow: (i) maximum muscle width (A, mm); (ii) maximum muscle depth (B, mm); (iii) subcutaneous fat depth above B (C, mm).Each joint was dissected into muscle, subcutaneous fat, inter-muscular fat, bone and remainder (major blood vessels, ligaments, tendons and thick connective tissue sheets associated with some muscles).

Statistical analysis
The carcass data were analysed using the mixed models procedure (proc mixed) of SAS (1998) an used location (L), sire breed (SB) and sex (S) as fixed effects and their interaction.The data were adjusted to constant cold carcass weight as linear covariate (Steel and Torrie, 1982).A Tukey's pairwise test was used to examine the significance of the differences between locations, sire breed and sex least-square means.

Carcass measurements
The least square means for treatments effects on carcass measurements are presented in Table 1.There was no signif icant (P > 0.05) effect of farm location on killing-out proportion, carcass perimeter measurements and on leg compactness indices.There was a significant effect of location on linear carcass measurements F (P < 0.05) and S (P < 0.01) without affecting (P > 0,05) other linear measurements.There was a location effect (P < 0,05) for longissimus muscle measurements, since carcasses from location 2 showed higher (P < 0.05) longissimus muscle width (A) than carcasses from location 1 and 3 and carcasses from location 3 presented higher (P < 0.05) subcutaneous fat thickness (C) than carcasses from the other two locations.
Sire breed did not affect (P > 0.05) killing-out proportion but changed the majority of other variables.Carcasses of Churra Galega Bragançana pure-breed lambs showed higher length measurements (K, P < 0.05; F, P < 0.05) and lower width measurements (Wr, P < 0.05; S, P < 0.05) than crossbred lambs.Carcasses of Merino Precoce and Suffolk crossbred lambs showed higher perimeter measurements (ACB, P < 0.05 and PCB, P < 0.05).Carcasses of Suffolk crossbred lambs had higher longissimus muscle width (A, P < 0.05) and no differences (P > 0.05) were found among genotypes in B and C measurements.Churra Galega Bragançana pure-breed lambs presented lower carcass (P < 0.05) and leg compactness (P < 0.01) indices (PCQ/K and G/F) than crossbred.Linear and perimeter measurements of carcasses were not affected (P > 0.05) by sex of lambs, although, carcasses of male lambs had greater muscle longissimus width and smaller (P < 0.05) subcutaneous fat thickness than the female lambs.Female lambs showed higher (P < 0.001) killing-out proportion than male lambs.Only the interaction location → sire-breed → sex for PCB measurement was signif icant (P < 0.05), which had little practical importance.

Carcass joints proportion
The least square means for treatment effects on carcass joints proportion are presented in Table 2. Carcasses from location 1 had higher (P < 0.05) leg proportion than carcasses from the other two locations.Carcasses from location 2 had higher (P < 0.05) KKCF proportion than the other two locations.

Carcass joints composition
The least square means for treatments effects on carcass joints proportion are presented in Table 3. Lambs from location 1 presented higher muscle proportion in all carcass joints but significant (P < 0.05) differences were only detected in leg, chump, loin, middle neck and in breast.Lambs from location 2 had lower (P < 0.05) subcutaneous fat proportion in the ribs than the lambs from the other two locations.Carcasses of lambs from location 3 showed higher inter-muscular fat proportion (P < 0.05) in some carcass joints, especially evident in chump, loin (P < 0.05) and breast (P < 0.05).
Carcasses of Suffolk crossbred lambs had lower (P < 0.05) muscle proportion on middle neck and no differences (P > 0.05) were found in all others joints.Suffolk crossbred lambs had lower (P < 0.05) subcutaneous fat proportion in the chump and in the loin carcass joints.No differences (P < 0.05) were found in intermuscular fat between sire breeds.
Male lambs showed higher (P < 0.05) muscle proportion in all carcass joints than female lambs, except for the middle neck joint where no differences (P > 0.05) were found.Female lambs showed a higher (P < 0.05) subcutaneous fat proportion in the loin and in the ribs.Female lambs had higher (P < 0.05) intermuscular fat proportion and lower (P < 0.05) bone proportion in all carcass joints than the male lambs, however, no differences (P > 0.05) were found in bone proportion of loin.

Carcass measurements
The killing-out proportion has a great importance in live animal commercialisation and is highly conditioned by food type and by gastrointestinal contents at slaughter time and, also, by fattening grade.The positive association between the fattening grade and killing-out proportion was already described by Kirton et al. (1995b).The highest killing-out proportion presented by lambs from location 3 can be explained by their higher fattening degree, which can be confirmed by the greater subcutaneous fat thickness (+0.7 mm), probably due to their slower growth rate, which led to a higher degree of maturity at slaughter, as described by Kirton and Morris (1989).As expected, female lambs showed higher killingout proportion than male lambs, due probably to their higher fattening degree when compared at the same carcass weight (Wood et al., 1983;Kirton and Morris, 1989;Jeremiah et al., 1997c;McClinton and Carson, 2000) as confirmed by their larger subcutaneous fat thickness and KKCF proportion.
The farm location effect on carcass conformation measurements, when compared at same cold carcass weight, was small and not important.The longest and thinnest carcasses presented by Churra Galega Bragançana lambs are in accordance to the expected results, since this is a local breed without selection pressure for carcass conformation.
Since Pálsson (1939) pioneer work carcass compactness indices have been used as objective indicators of carcass conformation.In this way, shorter and thicker carcasses show a more compact aspect, which can be advantageous, since it can improve consumer attractiveness to joints with higher muscle area, as pointed out by Hopkins et al. (1997).These authors observed that better conformation is associated to higher muscle:bone ratio.Nevertheless, the opposite was observed in this study, where Churra Galega Bragançana purebred lambs showed higher muscle: bone ratio, as previously published by Teixeira et al. (1996).These differences could be explained by the lower carcass weight used in this study.Kirton and Pickering (1967) did not find differences in meat content and in joint proportions between lambs with compact (bloky) or poor (leggy) conformation.This seems to be conf irmed by this study results, since sire breeds differences observed in compactness indices do not produce great differences in carcass joints proportion.
The higher muscle longissimus width presented by Suffolk crossbred carcasses can be an advantage, since it is associated to higher muscle area, which in turn is closely associated to carcass conformation.Joints with higher muscle area have better visual appreciation and higher consumers acceptability, as pointed out by Kempster (1983).On the other hand, several authors (Kirton et al., 1995b;Hopkins et al., 1997;Hopkins and Fogarty, 1998) found no differences in muscle longissimus area among carcasses from different sire breeds, mainly between Suffolk and Texel crosses.Kirton et al. (1995b), in a 10 years study in New Zealand, observed significant differences in muscle longissimus area among lambs of different sire breeds, when data were corrected to the same carcass weight.
The muscle longissimus width were 3 mm larger on male lamb carcasses than on female carcasses, which is contrary to Jeremiah et al. (1997a), who found no sex differences in this measurement.
The larger subcutaneous fat thickness presented by female lambs, when compared at the same carcass weight, supports the theory that male lambs, due to their higher growth rate, have less subcutaneous fat than female lambs as widely described in the bibliography (Jones, 1982;Kirton and Morris, 1989;Teixeira et al., 1996;Jeremiah et al., 1997a;McClinton and Carson, 2000).

Carcass joints proportion
The higher KKCF proportion for Churra Galega Bragançana pure-breed carcasses seems to confirm the theory that hill or ewe-type breeds have more internal body fat than specialised meat type breeds, as suggested by Kempster and Cuthberson (1977), Wood et al. (1980b) and Teixeira et al. (1996) and that crossbreeding can improve the fat distribution in carcasses.
Sire breed influenced the carcass joint proportion; however, the differences found, apart from being statistically different, were small.These results are in agreement to those attained by Hopkins and Fogarty (1998) who found significant differences in carcass joint proportion in a study with Texel, Poll Dorset, Border Leicester and Merino sire breeds mated to Border Leicester × Merino and Merino ewes.Cruickshank et al. (1996) also found differences between sire breeds in the higher valuable carcass joints.Fraser and Stamp (1989) attributes the breed differences for joint proportion to the higher lumbar and sacred vertebras growth in specialized meat type breeds.
Male lambs had higher leg and forequarter joint proportions than female lambs, mainly for neck and shoulder joints.On the other hand, they had lower KKCF and loin proportion than female lambs.These results seem to confirm those from Carpenter et al. (1969), who verified that female lambs and wethers produce carcasses with higher hindsaddle proportion than male lambs, probably as a result of the highest shoulders proportion in male lambs.On the other hand, Jeremiah et al. (1997c) found no significant sex differences on hindsaddle and longsaddle proportion; although these authors removed the KKCF fat from the carcass.In the same way, Jeremiah et al. (1997c) found no consistent differences in shoulders proportion (corresponding in our cutting system to the shoulder plus neck joints) among genders (male, female and wethers) due the different chronological age at slaughter.

Figure 1 .
Figure 1.Schematic representation of the carcass conformation measurements.

Figure 3 .
Figure 3. Schematic representation of muscle longissimus depth (B) and width (A) and subcutaneous fat thickness (C), adapted from Wood and MacFie (1980a).