Influence of Dietary Phosphorus Level on Growth and Bone Development in Boars and Gilts

The dietary phosphorus level supporting maximum growth rate was not greater than .40% for gilts, but for boars was between .4 and .6%. However, for maximum development of the radius and femur, gilts required more than .4% and boars more than .6%. In the First experiment a corn-soy bean meal diet containing .9% calcium and .32% phosphorus was supplemented with phosphorus to .36, .40 and .44%. Three pens of four boars received each diet from weaning to 90 kilograms. Growth increased from 630 to 822g/day when the phosphorus level was increased from .32 to .40%, but bone development responded to all three increments of phosphorus. In the second experiment a diet containing .8% calcium and .4% phosphorus was supplemented with phosphorus to .6, .8 and 1.0%. Three pens of eight gilts and three pens of eight boars received each diet. Increasing the phosphorus level from .4 to .6% improved the gain of the boars from 798 to 875g/day, but there was no response for the gilts. The force required to break the femurs responded in the same way, increasing for the first dietary phosphorus increment for the boars, but not changing significantly for the gilts. Analyses of 10 batches of each diet showed the extent of between and within mix variation encountered in nutritional experiments.