The effect of breed (Large White × Landrace ν. purebred Meishan) on the diets selected by pigs given a choice between two foods that differ in their crude protein contents

Abstract

AbstractTwo pig breeds, one improved (Cotswold Fl hybrid Large White × Landrace pigs = LWX) and the other unimproved (Chinese Meishan pigs = CM) were used to test the proposition that the genotype of the pig has an effect on the selection of a diet from two foods that differ in their crude protein content. From 21 to 34 kg live weight, the pigs were given access to either one of three foods or a choice of two foods with similar digestible energy concentration (16 MJ digestible energy per kg) but a different crude protein (CP) concentration. This resulted in four dietary treatments: (i) free and continuous access to low (L) crude protein food alone (130 g CP per kg, no. = 4 of each breed); (ii) free and continous access to high (H) crude protein food alone (252 g CP per kg, no. - 4 of each breed); (Hi) free and continuous access to moderate (M) crude protein food alone (206 g CP per kg, no. = 4 of each breed) and (iv) free and continuous access to both foods L and H as a choice (no. = 6 of each breed). On all treatments the LWX performed significantly better than the CM pigs in terms of live-weight gain and food conversion efficiency (P< 0·001). The LWX and CM pigs given access to a single food contained the same amounts of protein in their bodies at 34 kg live weight, but the CM pigs had a considerably higher lipid (P< 0·001) and a lower water content (P< 0·001). When given a choice, the LWX pigs selected a significantly higher proportion of foodH(521v.226 (s.e.d. 49) g food H per kg for LWX and CM respectively) and therefore, a higher CP content in their diet (194v.144 (s.e.d. 5·4) g CP per kg respectively) than the CM pigs. The performance of pigs given a choice between two foods, in terms of live weight and rate of protein gain, was comparable with the best performance achieved on a single food (M) for the LWX, and better than the best performance on a single food (L) for the CM pigs. Thus, when given a choice between an appropriate pair of foods that differ in their crude protein content, pigs are able to select a diet that meets their requirements and allows them to express the growth characteristics typical for their breed (genotype).