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- Title
Importance of body composition in explaining variation in feed conversion efficiency and residual feed intake between sheep.
- Authors
Knott, S. A.; Leury, B. J.; Cummins, L. J.; Dunshea, F. R.
- Abstract
Background -- The efficiency with which an animal utilises energy during growth, is dependent on a number of physiological factors including body composition and the relative proportions of lean tissue mass (LTM) and fat tissue mass (FTM), due to differences in the energy cost of depositing and maintaining these tissues. However, the relationship between body composition and maintenance energy expenditure in sheep is less clear. Objective -- To determine the relationship between feed conversion ratio (FCR, kg feed:kg gain) and residual feed intake (RFI) with body composition in rams at six months of age. Design -- Whole animal body composition, using dual energy X-ray absorptiometry (DXA) was measured in 52 crossbred rams (6mo, 36 kg) at the start and end of the study. The individually-housed rams were fed ad libitum pellets (12 MJ/kg DM, 16% CP) with feed intakes and live weights recorded for 49 d. Feed conversion efficiency was calculated as feed eaten:liveweight gain (FCR). To calculate RFI, feed intake is regressed against mean metabolic liveweight (W0.75) and average daily gain, with the residual portion, used as the measure of efficiency. The more negative the RFI value, the more efficient the animal is. Restricted maximum likelihood (REML) analysis was used to develop models relating body composition to either FCR or RFI. Outcomes -- LTM at the start and end of the study accounted for 66% of the variation in FCR, yet only accounted for 3% of the variation in RFI. FTM at the start and end of the study accounted for 11% of the variation in FCR, and none of the variation in RFI. Conclusions -- LTM is a major determinant of FCR in young sheep. Given that FCR is primarily a function of growth, and sheep at this age typically deposit more lean tissue over fat tissue, this result is not surprising. However, the nonsignificant relationship between RFI and body composition in sheep at 6mo, suggests that efficiency of energy use is independent of composition and is driven by other physiological functions.
- Subjects
BODY composition of sheep; FEED utilization efficiency; SHEEP; ANIMAL nutrition; NUTRITION
- Publication
Asia Pacific Journal of Clinical Nutrition, 2005, Vol 14, pS78
- ISSN
0964-7058
- Publication type
Article