Modelling lactation curves of Friesian cows in a subtropical climate

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Abstract
Monthly herd recording data from Friesian cows in south-east Queensland are used to evaluate 20 models of the lactation curve, 10 being drawn from the literature and 10 being original. The curve of Wood (1967) with equation y =a nb exp(–cn),and its modificationy =a nfc/cosh(en), generally gave the lowest values for the error mean square across all seasons of calving. However, the model which predicts a constant initial yield, followed by a linear decline,y =a forn =Sc, y =a - b(n –c) forn > c, is as good as the previous two models for winter calving cows. Hence it is a useful representation of the lactation curve in south-eastern Queensland, where about 40% of cows are calved in winter. The inverse polynomial modely =nl(a +bn + en2) is a useful model for lactations commencing in the summer months.