The objective of this study was to describe the characteristics of dairy farms with different concentrations of unsaturated fatty acids (UFA) in milkfat using a stochastic farm model. Daily phenotypic cow performance was simulated using an exponential function including terms for milk, fat, protein and live weight, and a third order orthogonal polynomial of milkfat UFA concentration. Daily and yearly feed requirements were estimated from metabolisable energy requirements for maintenance, lactation, pregnancy and growth. Two groups of farms were simulated: (1) Average UFA farms (30 farms, milkfat UFA concentration = 30.04 g/100g milkfat) and (2) High UFA farms (30 farms, milkfat UFA concentration = 35.99 g/100g milkfat). Each farm was 140 ha and had 386 cows, a replacement rate of 18% and a spring calving between 20 July and 10 September. The simulation was replicated 1,000 times. High UFA farms produced significantly (P < 0.05) less milkfat (338 vs 502 kg/ha) and milksolids (692 vs 927 kg/ha) than Average UFA farms. This resulted in High UFA farms having lower (P < 0.05) gross farm income ($3815 vs $5075 /ha) and cash operating surplus ($-331 vs $598/ha) than Average UFA farms. This highlights the need to develop a payment system that rewards concentration of UFA in milkfat.
Proceedings of the New Zealand Society of Animal Production, Volume 72, Christchurch, 175-180, 2012
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