Effect of varying levels of concentrate supplementation on growth performance and carcass traits of finisher lambs

S A Karim, M K Tripathi* and V K Singh

Central Sheep and Wool Research Institute, Avikanagar (via-Jaipur)
Rajasthan, 304 501 India
mktirpathi@gmail.com

Abstract

The slaughter study was conducted on finisher lambs drawn from a growth trial on weaner lambs maintained on grazing with concentrate supplementation of 1.5 (C1.5) and 2.5 % (C2.5) of body weight and ad-libitum concentrate (C-AL) in cafeteria system of feeding management of 90 days duration during active phase of growth to assess their carcass traits.

Weaning weight was similar in the three groups (13.9 kg) while the finishing weight was higher (P<0.01) in C-AL (27.2 kg) than C2.5 (23.2 kg) and C1.5 (20.9 kg). Level of concentrate feeding improved daily gain and feed efficiency. The empty live weight, hot carcass weight and weight of edible offals of the 3 groups also followed trend similar to that of pre slaughter weight. The dressing yield, both in terms of pre slaughter weight as well as empty live weight, although statistically similar in the three groups. The dressing yield inclusive of edible offals in terms of empty live weight (ELW) was however significantly (P<0.05) higher in C-AL than C1.5 and C2.5. The total edible and inedible offal yield as % of pre slaughter weight (PSW) was similar in the three groups (4.79 and 34.67 % of PSW). The cut weights of the primal cuts were higher in C2.5 and C-AL than C1.5 whereas as % of PSW the cut proportions were similar in 3 groups excepting leg cut which was similar in C2.5 and C-AL and significantly (P<0.01) higher in C1.5. The chilling loss % was higher in loin and rack than other primal cuts with an average of 2.7 % chilling loss of the half carcass. The lean content of primal cuts was similar in the three groups while the loin fat content was 10.3 % in C1.5, which increased (P<0.05) to 14.1 and 19.5 %, respectively in C2.5 and C-AL.

It is concluded that the growth performance was better under cafeteria system of feeding management than grazing with 1.5 or 2.5 % of body weight as concentrate supplementation. Moreover under cafeteria system of feeding management the feed conversion efficiency improved while half carcass fat content remained well within limit (9 %) providing a carcass of desired quality thus rendering the production system suitable for commercial application. Better performance of C-AL lambs was the reflection of higher concentrate intake, however higher feed cost per kg meat was incurred.

Key words: carcass traits, concentrate supplementation, growth, lambs

Introduction

Under the existing land utilization in the country sheep are traditionally reared on grazing with top feed supplementation during critical summer months. The male lambs in farmers flock surplus to the breeding requirement are disposed off for slaughter at 9- 12 months of age weighing 22 kg (Karim 2004) with average carcass weight of 10- 11 kg (Kondaiah and Agnihotri 1995). The male lambs under field condition have poor growth rate and in active phase of growth (3- 6 months) attain 60- 70 g average daily gain (Kaushish et al. 1990) while these native lambs under intensive feeding management are able to attain 150 g average daily gain (Karim and Rawat 1996) indicating that the feeding management has to be optimized for enhancing mutton production.

Carcass evaluation is essential for growth studies to determine relative efficiency of finisher lambs in converting feed to animal tissue. The slaughter traits, in turn are modulated by heredity, feeding regimen and prevailing rearing environment. It is however realized that for practical meat disposal in the country, the western concept of meat grading is not practiced as different primal cuts do not fetch variable market prices. Indian consumers usually prefer meat with desired fat content (12- 15 %) whereas fat content exceeding 20 % is not liked by the locals. Moreover higher fat deposition in the carcass reduces the feed conversion efficiency thus increasing the cost of feed input/kg gain in live weight and hence is uneconomical. A series of slaughter studies conducted at the station on finisher lambs drawn from breeding and feeding experiments indicated that the native lambs in farmers flock have dressing yield (Ratio of hot carcass weight to pre slaughter weight) of 40 % which increased to 50 % under organized feeding management (CSWRI 1998). Moreover the dressing percentage was generally higher in lambs maintained under high level of feeding than their range managed/low plane fed counterparts (Katiyar et al. 1974; Krishnamohan and Chryalu 1983; Sen et al. 2000).

The reported slaughter study was conducted on finisher lambs drawn from a growth trial on weaner lambs maintained on grazing with varying level of concentrate supplementation and cafeteria system of feeding management to assess their carcass traits.
 

Materials and methods

Sixty weaner (About three months old) were adopted from a local farmer adopted under Jaivigyan Project. The lambs were dewormed and vaccinated against enterotoxaemia and divided into 3 equal groups. The lambs were maintained in groups in separate enclosures under a side open asbestos roofed animal shed for further 90 days. They were fed under cafeteria system of feeding management and offered ad lib. roughage (Prosopis cineraria and Albizia lebbeck leaves in ratio of 50: 50) in feeding troughs during morning hours. Residue, if any, of the previous day was weighed and discarded the next day before fresh feed offer. Besides ad lib. roughage the C1.5 and C2.5 lambs were offered concentrate (Maize 29, GN cake 30, wheat bran 20, de oiled rice bran 18, mineral mixture 2 and common salt 1 parts) of1.5 and 2.5 % of body weight, respectively while the C-AL lambs were maintained under cafeteria system of feeding management with free choice concentrate and roughage in separate containers. The feeding experiment continued for 90 days followed by a slaughter study on 6 finisher lambs from each group to assess carcass traits.

The lambs were fasted for 18 hrs with free access to water and slaughtered as per the standard procedures by Halal method. Carcass, edible (Testicle, spleen, pancreas, mesenteric fat, caul fat, kidney fat, kidney, heart, liver) and non edible (Head, skin, fore and hind canons, lungs with trachea, gall bladder, penis, empty GI tract) offal weights were recorded immediately after slaughter. Lungs, trachea and heart were weighed as one piece and designated as pluck. Weight of ingesta was determined as the difference between full and empty digestive tract. The empty live weight was computed as the difference between pre slaughter weight and weight of digestive content. The hot carcass was then split to fore and hind quarters. The fore and hind quarters were further split along the mid line and the left half was disjointed as per ISI (1963) specifications to standard cuts viz. leg, loin, rack, neck and shoulder and breast and fore shank. The cuts were chilled over night at 4°C and the next day the cuts were dissected into lean, fat and bone which was expressed as proportion of chilled weight of the various cuts. The dissected bones of different cuts were boiled for 15 mins in 2 % KOH solution and KOH bone content was determined. Loin eye area (cm²) was recorded on the cut surface of Longissimus dorsi muscle at the interface of 12^th and 13^th ribs on both the sides of the carcass.

The data generated in the experiment were subjected to analysis of variance and significant group differences were compared using SPSS 10 package.
 

Results and discussion

Weaning weight was similar in the three groups (13.9 kg) while the finishing weight was higher (P<0.01) in C-AL (27.2 kg) than C2.5 (23.2 kg) and C1.5 (20.9 kg), similar trend was for average daily gain and feed efficiency (Figure 1).

Figure 1.  Effect of level of concentrate feeding (C1.5, 1.5 % of LW; C2.5, 1.5 % of LW; C-AL, ad-libitum) on average daily gain (ADG) and feed efficiency (%, g gain/ 100g feed intake)

Initial live weight of lambs were similar but concentrate supplementation significantly increased gain and feed conversion ration with increase in concentrate supplementation (Table 1)

Higher growth rate in high concentrate fed lambs was due to better plane of nutrition which was also observed by Santra et al. (2002). The results indicated that farmer’s weaner lambs have higher growth potential under cafeteria system of feeding management than those reported for the genotype maintained under extensive range management (Kaushish et al. 1990).

The pre slaughter weight reflected the trends of finishing weight of the three groups which was also higher (P<0.01) in C-AL followed by C2.5 and C1.5, in that order (Table 2).

The empty live weight, hot carcass weight and weight of edible offals of the 3 groups also followed trend similar to that of pre slaughter weight. The dressing yield, both in terms of pre slaughter weight as well as empty live weight, although statistically similar in the three groups, was generally higher in C-AL than other two groups. The dressing yield inclusive of edible offals in terms of empty live weight (ELW) was however significantly (P<0.05) higher in C-AL than C1.5 and C2.5. The range of dressing yield of the lambs observed in the study was similar to earlier reports on Indian sheep (Karim and Rawat 1997; Karim et al. 2002; Sen et al. 2004). The loin eye area as index of muscle growth was similar in the three groups (12.8 cm²) indicating that tissue accretion of even C1.5 was optimum for the genotype.

Edible organ weight, kidney fat and caul fat content was generally higher in high concentrate fed groups which was reflected in higher (P<0.01) total edible offal weight in C-AL followed by C2.5 and C1.5 in that order (Table 3).

The total edible offal weight expressed in terms of pre slaughter weight was however similar in the three groups (4.79 % of PSW). Likewise the inedible offal weights and total inedible offal weight were also higher in C-AL than C2.5 and C1.5 whereas on expression of total inedible offal weight in terms of pre slaughter weight, the differences were non significant with over all average of 34.67 %. The higher edible and inedible offal weights of C-AL and C2.5 than C1.5 reflected the variation in their pre slaughter weight which got rationalized on expression in terms of pre slaughter weight hence the difference was found non significant.

The data on primal cuts and percent yield of half carcass are presented in Table 4.  The cut weights of the primal cuts reflected the trend of pre slaughter weight and were higher in C2.5 and C-AL than C1.5.