The relative protein and energy requirements of boars, gilts and barrows

Abstract

Two experiments were conducted to study the response of boars, gilts and barrows to increasing levels of dietary crude protein and digestible energy. In the first experiment boars, gilts and barrows were fed diets ranging in crude protein from 14.6 to 22.7 per cent in restrictive amounts between 20 and 70 kg liveweight. Growth rate and food conversion efficiency measurements ranked the sexes in order of superiority as boars, gilts and barrows. Boars contained more lean in their hams than gilts or barrows and had lower back fat measurements than barrows. Although analysis of variance indicated there was no significant sex by protein interaction, the multiple regression equations of growth rate and the proportion of lean in the ham for the three sexes were significantly different from one another. The response curves based on the regression equations indicated that for optimum growth, boars and gilts required 19.6 per cent crude protein whereas barrows required only 18.4 per cent crude protein. The proportion of lean in the ham was maximized with 21 per cent crude protein for boars and 20 per cent crude protein for the gilts and barrows. There was a significant quadratic relationship between economic returns and dietary protein. The relationship was the same for boars and gilts and significantly different from that for barrows; returns were maximized at approximately the same protein level as growth rate for the three sexes. In the second experiment, 30 boars and 30 gilts were allocated to 30 treatment groups involving the two sexes, three levels of digestible energy (14.59, 15.51 and 16.22 MJ kg-1) and five levels of crude protein (18.2, 19.4, 20.6, 21.8 and 23.0 per cent). All diets were fed restrictively and pig performance was compared over the liveweight range 20 to 80 kg. Boars grew significantly faster, had a significantly lower food conversion ratio and produced leaner carcases than gilts. Increasing the DE level of the diet improved growth rate and food conversion efficiency but reduced carcase quality. Dietary protein level had no effect on any performance or carcase quality measurement.