A sheep intake model was adjusted for dairy cows and used to illustrate intake in relation to inherent hunger, days in milk (DIM), and herbage allowance. Intake is predicted by an exponential function of pregrazing herbage mass, stocking density and hunger drive (k). In adjusting the model, k was re-parameterised using a data set of n = 1,198; it was then adjusted to represent intake decline from peak to end of lactation. This adjustment resulted in splitting k into a and b. Parameter a represented inherent hunger and b its persistence during lactation. The re-parameterised model was tested against an independent data set (n = 287). The square root of mean prediction error was 1.57, indicating good prediction accuracy. Data from three different cow strains, New Zealand-70 and -90 and North American-90 (n = 210, 293 and 271, respectively) were used to reestimate a and b, and to illustrate inherent hunger drive. a and b differed (P <0.01) between strains. Then, with the adjusted and re-parameterized models, the interaction effect of herbage allowance, strain, and DIM on intake were simulated. The adjusted model offers an easy-to-use tool to compare, interpret and illustrate feeding scenarios.

P, Gregorini, AJ Romera, PC Beukes, JL Rossi, and KA MacDonald

Proceedings of the New Zealand Society of Animal Production, Volume 69, Christchurch, 28-31, 2009
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