Feed conversion efficiency (FCE) and seasonality of feed demand were assessed within a demand-driven deterministic steadystate model of a sheep livestock system. Weekly animal feed demands were simulated within ExcelTM. Overall flock structure and seasonality of demand were then determined using linear programming. Key inputs were individual animal energy requirements (MJME) for maintenance, pregnancy, lactation and growth. Whole-of-system FCE was measured as grams of meat carcass per MJME. Overall system output was constrained by a fixed but arbitrary system limit of 10 million MJME. Increasing the lambing percentage from 110% to 170% increased FCE by 20%, with less total system feed required during the pregnancy period but with more feed required post-weaning. Increasing pre-weaning liveweight gain from 250 g/day to 450 g/day increased FCE by only 1%, but with a transfer of feed demand from post-weaning to pre-weaning. Increasing post-weaning liveweight gain from 100 g/day to 300 g/day increased FCE by 8% with earlier slaughter reducing overall post-weaning requirements. Increasing carcass weight from 12 kg to 24 kg increased FCE by 28%, with a major shift in feed demand from pre-weaning to post-weaning. Implications for improving pastoral sheep farm productivity and profitability are discussed.
Proceedings of the New Zealand Society of Animal Production, Volume 75, Dunedin, 9-14, 2015
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