Empirical algebraic modelling of lactation curves using Irish data

The purpose of this study was to find a well-fitting, robust, single-equation model to describe the shape of lactation curves for Irish dairy cows. The suitability of a number of algebraic models that depict lactation curves was examined, using Irish test day data. The analysis was carried out on a total of 14,956 lactation records from commercial and experimental herds and included both autumn and spring calving animals. ‘Goodness of fit’ and adherence of the various models to the assumptions of regression analysis were examined. Multicollinearity posed a severe problem in the application of the best-fit model but omitting one of the variables from the estimation procedure reduced this effect. The modified model, referred to as the Ali-B model, is a single equation model that can be easily updated and incorporated into computer code. This is in contrast with the Standard Lactation Curve (SLAC) method, a method of interpolation, which is currently used by the Irish industry. The effects of seasonal factors on milk production were estimated and added to the Ali-B model to create a production profile for cows calving in specific months. The Ali-B model provided an acceptable level of accuracy in representing the shape of the lactation curve for Irish dairy cows, and can be easily modified for different environmental scenarios.