Growth rate and its effect on empty body weight carcass weight and dissected carcass composition of sheep
Murray, D.M.; Slezacek, O.
Journal of Agricultural Science 87(1): 171-179
ISSN/ISBN: 0021-8596 DOI: 10.1017/s0021859600026721
The effect of 3 different growth rates from 15-40 kg live weight on the body composition of lambs was studied. The treatments were High (H) ad lib feed intake, Low (L) restricted feed intake and High-Maintenance-High (HMH) ad lib feed intake from 15-25 kg followed by a 50 day period during which live weight was maintained constant, which in turn was followed by ad lib feeding. The animals were individually penned and fed a pelleted lucerne chaff-cereal grain mixture. Two animals were killed at the start of the experiment (15 kg) and the remaining 27 animals (9 in each treatment) were killed at common live weights of 25, 30, 35 and 40 kg. Analyses of covariance were used to compare linear regression equations representing results from each treatment using the logarithmic transformation of the allometric equation, y = axb. Animals in the H and L treatments had a mean growth rate from 15 kg until slaughter of 0.23 and 0.09 kg/day, respectively. From a live weight of 15-25 kg, the HMH group grew at a similar rate as the H group, i.e., 0.22 and 0.21 kg/day, respectively. After the 50-day period of maintenance of live weight, the HMH animals killed at 30, 35 and 40 kg showed a marked compensatory growth response to ad lib feeding. These HMH animals had a mean growth rate of 0.37 kg/day compared with 0.26 kg/day for H animals over identical live-weight ranges. Empty body weight (EBW) formed a similar proportion of full body weight (FBW) in all 3 treatments. As a proportion of FBW, hot carcass weight (HCW) was similar in the H and L treatment, while at the 35 and 40 kg slaughter weights HCW was less in the HMH than in the H treatment. HCW also formed a lower proportion of EBW at the 35 and 40 kg slaughter weights in the HMH, than in both the H and L treatments. In the L treatment, HCW formed a greater proportion of EBW than in the H treatment, indicating a greater offal component of EBW in the H animals. At the same dissected side weight (DSW), the amount of muscle, bone, connective tissue and total side fat (TSF) was similar in the 3 treatments. Although no differences were found between treatment in TSF, there were significant treatment effects on both the subcutaneous and inter-muscular fat depots. Animals in the H treatment had more and less, respectively, subcutaneous and intermuscular fat than the L animals. The amount of intermuscular fat was also greater in the HMH than in the H treatment.