Mathematical equations to describe lactation curves for Holstein- Friesian cows in New South Wales

Abstract

Researchers have characterised dairy milk production using a wide variety of statistically estimated equations that regress the average yield per unit time of cows in a given parity against time. The various functions employed to explain average daily milk yield include the incomplete gamma, the inverse polynomial, the Mitscherlich exponential form, and the multiphasic curve. Most of the lactation research has been carried out in the Northen Hemisphere and the applicability of the results to Australian conditions is limited due to differences in herd and feed management practices. The usefulness of some functions in developing management strategies is also limited, as it is difficult to determine lactation characteristics, such as time to peak yield and the milk production at this peak. Herd recording data from New South Wales were used to estimate equations for ‘average’ Holstein-Friesian dairy cows of varying parities. Of the 4 functions used in this study, one was not statistically appealing, the multiphasic function, and of the others, 2 functions, the incomplete gamma function and the inverse polynomial, performed well statistically and in replicating the underlying data. Thus, the simplest functions were more robust.