Phosphorus in the feeding of pigs : effect of diet on the absorption and retention of phosphorus by growing pigs

An extensive review is given of the literature concerning phosphorus feeding of pigs. Subjects dealt with are: 1. physiological background, regulation and effect of diet composition and nutrient supply on phosphorus absorption and retention; 2. estimation of the amount of P present in the bodies of pigs using several models and 3. estimations of the P requirements of slaughter pigs from results of balance and slaughter experiments.In the own experiments -using balance, slaughter, digestibility and feeding trials- on growing pigs the following aspects were studied: accuracy of measurements ; P absorption and retention as related to diet composition and nutrient supply; the effects of reduced P supply on performance and, possibly, on locomotory disturbances. It was shown that in phosphorus balance studies, because of carry-over effects, the adaptation period should be at least 21 days when there is a substantial change in phosphorus supply. Effects of dietary energy and protein on P absorption and retention could best be explained by their effect on the daily amount of protein and fat retention. The retention of P measured by the balance was only six per cent (25 + 17 g P) higher than measured by the comparative slaughter technique. Animals with a normal type of daily gain retained 5.0 to 5.1 g P/kg live weight gain, those with a leaner gain 0.2 to 0.3 g P/kg live weight gain more.A technique was described to measure the digestibility of P in various feedstuffs and feed phosphates; substantial differences in digestibility of P between various feedstuffs and feed phosphates were observed. Maximal utilization of P was found at a dietary Ca/digestible P ratio between 2.9 and 3.5.In various feeding trials, leg weakness was not observed any more frequently when slaughter pigs from 30 kg live weight onwards received diets with very low concentrations of phosphorus (g/kg feed) and calcium. However, calcification of the bones was poorer than that of the control animals.Both optimal and just sufficient P requirements for slaughter pigs, were derived. These were expressed as the concentration of digestible P per kg diet.