Energy: protein interactions in growing boars of high genetic potential for lean growth. 1. Effects on growth, carcass characteristics and organ weights

Abstract

AbstractSeven replicates of five littermate boar Landrace pigs were used to evaluate the effects of (a) reducing the food intake within the practical range or (b) reducing energy intake without reducing protein intake, between 33 and 90 kg live weight on growth, nitrogen balance and carcass characteristics. Three levels of food intake (ad libitum, 0·90 and 0·80ad libitum) were used and the dietary protein contents ranged from 250 to 312 g crude protein per kg dry matter (DM) to equalize protein intake with reduced food intake. All the diets were of similar amino acid composition, and lysine per kg DM ranged from 14·3 to 17·9 g. The food was given twice daily. Balance trials were conducted at 45 and 65 kg live weight and all pigs were slaughtered at 90 kg live weight to assess carcass characteristics. Reducing food intake or only energy intake significantly reduced live-weight gain (P< 0·001). Reducing food intake decreased nitrogen retention (P< 0·01) during the 65-kg balance period. Reducing food intake had no effect on fat thickness measurements but measurements at shoulder (P< 0·001), mid back (P< 0·001), C(P< 0·01) and P2 (P< 0·05) decreased and lean: fat in rumpback increased (P< 0·05) when energy intake was reduced. The weights of small intestine (P< 0·001), large intestine (P< 0·05), liver (P< 0·05) and kidneys (P< 0·05) were significantly reduced as food intake was reduced. Energy is more limiting than protein when the intake of a diet providing for optimal growth of high potential boars is reduced between 33 and 90 kg live weight.