Modelling the dietary calcium requirement of reproductive sows and variation in dietary calcium: phosphorus ratio with performance level

Due to the relative high mineral phosphate cost and the consequences of phosphorus supplied in excess on the environment, a strong trend towards improved adequacy between its supplies and requirements has been observed for a while in reproductive sows. Conversely, calcium mineral sources are relatively cheap, and the dietary calcium level is not limited by any regulation. As calcium and phosphorus interact in the digestive tract and in their metabolism, their supplies need to be balanced. Based on available literature on phosphorus (large) and calcium (scarce), a model was developed that assesses calcium requirements in reproductive sows. Due to difficulties in the assessment of the degree of bone mineralization in practice, the present version of the model cannot be used to simulate consequences of inadequate supplies of calcium or phosphorus. Phosphorus can be supplied on a digestible basis with reference to tables of nutritive values of feedstuffs, but this is presently not the case for calcium. Consequently, different hypotheses for calcium digestibility are used in the model, which will need to be updated (as well as the definition of the maintenance requirement). Given these limitations, the model is used to investigate the effect of physiological stage and productivity level (prolificacy, milk production) on the daily requirement of calcium.