Sheep and beef farmers target an increase in lamb growth rates as a means of increasing on-farm profit. Increasing any performance parameter invariably increases feed demand, resulting in either a need to increase feed supply or reduce feed demand in some other area of the farm system, therefore potentially affecting profit. A whole-farm-system model was used to assess the impact of increasing lamb weaning weight and post-weaning growth rate on farm profit and enterprise selection of three farms from three regions (Otago, Gisborne and Northland). Farm profit did not always increase with an increase in weaning weight or post-weaning growth rate. Farm profit was highest in the cool temperate region when weaning weight was at the base weight (27 kg) and post-weaning growth rate was 75 g/d greater than current. Farm profit was highest in the dry temperate region when weaning weight was 32 kg (6 kg above the base weight) and post-weaning growth rate was 50 g/d greater than the base growth profile. In the warm, temperate region, farm profit was highest at the two extremes, the highest weaning weight (30.6 kg) and post-weaning growth rate profile (100 g/d greater than the base profile) and at the lowest weaning weight (24.6 kg) and post-weaning growth rate profile (50 g/d less than the base profile). This demonstrates the interactions and trade-offs between feed supply and lamb growth rate on farm, and highlights that increasing lamb liveweight gain does not necessarily equate to increased profit.
Proceedings of the New Zealand Society of Animal Production, Volume 76, Adelaide, 132-136, 2016
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