Relationship between organ weight, carcass lean, net feed intake and gross feed conversion efficiency in composite sire line sheep. (Abstract)

Abstract

7A Relationship between organ weight, carcass lean, net feed intake and gross feed conversion efficiency in composite sire line sheep S.A. Knott1,3, F.R. Dunshea2, L. Cummins1, F.D. Brien1 and B.J. Leury 1 2 3 3 Pastoral and Veterinary Institute, Department of Primary Industries, Hamilton Vic 3300 Victorian Institute of Animal Science, Department of Primary Industries, Werribee Vic 3030 Institute of Land and Food Resources, Melbourne University, Parkville Vic 3052 Stephanie.Knott@nre.vic.gov.au Net feed intake (NFI) and gross feed conversion ratio (FCR) are commonly used to identify animals that are more efficient at converting feed into meat. NFI has been shown to be moderately heritable and negatively correlated with carcass lean in cattle (Herd and Bishop 2000). Visceral organs make a substantial contribution to whole animal energy expenditure (Baldwin et al. 1985). In particular, the gastrointestinal tract (GIT) and liver account for 4050% of wholebody cardiac output, protein synthesis and heat production (Davis et al. 1981; Webster 1981). This preliminary study examined the hypothesis that variation in the efficiency of energy utilisation in growing sheep, and therefore NFI and FCR, may be explained by differences in organ size and carcass lean. Eleven ram lambs of a composite sire line,11 months old, 41.8 kg mean liveweight, were individually fed a concentratebased diet (metabolizable energy 12 MJ/kg DM; crude protein 16% DM). Twice weekly body weight and total dry matter intake (TDMI) were measured for 41 d. After 41 d, animals were slaughtered and individual organ weights were recorded. Total organ mass was calculated as the sum of the empty GIT, liver, pancreas, spleen, heart and lungs. Carcasses were boned out into lean, fat and bone to the retail level. NFI calculation was based on the difference between actual feed consumed and the feed consumption predicted from the animals calculated requirements for maintenance and growth. Differences were observed between animals for visceral organ weights, NFI, FCR, ADG and TDMI (Table 1) but there were no significant correlations between total organ mass, nor individual organ weights, with NFI or FCR. ADG was highly correlated with FCR (r = 0.668, P<0.05) and with TDMI (r = 0.821, P<0.001), but it was not significantly correlated with NFI. NFI was negatively correlated with boneout lean tissue mass (r = 0.614, P<0.05). We conclude that variation in carcass lean but not total and individual or gan mass was related to differences in NFI between these animals. These results are consistent with those from work with beef cattle, but should be confirmed with larger numbers of animals. Baldwin, R.L., Forsberg, N.E. and Hu, C.Y. (1985). Potential for altering energy partition in the lactating cow. Journal of Dairy Science 68, 33943402. Davis, S.R., Barry, T.N. and Hughson, G.A. (1981). Protein synthesis in tissues of growing lambs. British Journal of Nutrition 46, 409419. Herd, R.M. and Bishop, S.C. (2000). Genetic variation in residual feed intake and its association with other production traits in British Hereford cattle. Livestock Production Science 63, 111119. Webster, A.J.F. (1981). The energetic efficiency of metabolism. Proceedings of the Nutrition Society 40, 121128. Table 1 Mean (� SD) results of ram lambs for ADG, TDMI, NFI, FCR, and selected organ weights. ADG (g/d) 484 (81) 1 TDMI (kg) 80.2 (9.9) NFI FCR1 Total organ mass (g) 6794 (604) Liver mass (g) 1085 (143) Total GIT (g) 4123 (450) Bone_out carcass lean (kg) 18.17 (1.8) _0.419 (0.18) 4.09 (0.46) kg DM/kg gain Recent Advances in Animal Nutrition in Australia, Volume 14 (2003)