Our objectives were to investigate how a cow model, "Molly", deals with once-a-day milking and to use "Molly" in a Whole Farm Model to explore farm systems where once-a-day milking might produce results on a per hectare basis comparable to twice-a-day milking. We compared our model outputs to observed data from a Milking Frequency trial run by Dexcel at a research farm in Taranaki. Changing the rate constants for milk removal and degradation of the lactation hormone complex in "Molly" resulted in the model expressing the acute and chronic effects of once-a-day milking. The once-a-day cow model fed ad lib seasonal grass pasture showed a decrease in milksolids yield (kg/cow) of 31% in Friesians compared to the observed 28%. When we used .Molly. in the Whole Farm Model it showed that farm performance with once-a-day milking was 1135 kg milksolids/ha when a Friesian herd was stocked at 7% higher and their lactation was extended by 14 days compared to a twice-a-day herd (1132 kg milksolids/ha). We conclude that farm performance with once-a-day milking is strongly dependent on selecting cows with higher lactational persistence under once-a-day milking and managing for extended lactations.
Proceedings of the New Zealand Society of Animal Production, Volume 64, Hamilton, 237-240, 2004
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