Modelling the dynamics of feed intake in growing pigs; interest for modelling populations of pigs

Modelling approaches are more and more used as an alternative to animal experimentation. Growth models are most often based on the prediction of feed intake, the efficiency of nutrient utilization, and the phenotypic potential of the animal. The drawback of these models is that feed intake is described by an empirical function of body weight and that variation between pigs is ignored. The aim of the present study was to compare four functions describing feed intake (linear, power, exponential or the gamma function) and to characterize the relation between parameters describing growth in a population. Seven batches of 144 growing barrows and gilts each, originating from crossbred LWxLD sows and eight purebred or crossbred sire lines were used. The pigs were weighed at 10, 13, 16, 19, 21 and 23 weeks of age and their individual feed intake was recorded daily through an automatic feed dispenser. For each equation, models were fitted individually to the data and the quality of the prediction was evaluated by the root mean square error of prediction. The gamma function provided the most precise fit of the data irrespective of genotype and gender. The gamma function is the “least-empirical” one and expresses feed intake relative to the maintenance energy requirement, implying that animals eat for maintenance once they are mature and non‐productive. Based on this model, eight parameters define an individual profile.Some relations between parameters have been shown, while some others are considered independent. This will allow the generation of virtual batches built on a realistic variation structure. These virtual batches will allow later stochastic simulations, taking into account individual variation in the response of the batch.