The effect of body weight on the upper limit to protein deposition in a defined population of growing gilts.

Abstract

In a stress-free environment and given adequate intakes of essential nutrients, protein deposition (PD) in growing pigs is determined by either energy intake or the genetically determined upper limit to body protein deposition (PDmax). In this experiment, the effect of metabolizable energy (ME) intake on PD was determined in 24 female pigs between 25 and 70 kg BW. Casein and cornstarch-based diets that were not limiting in any of the essential nutrients were offered semi-ad libitum (12 pigs) or restrictively at 1.8, 2.2, or 2.6 times the ME requirements for maintenance (MEm; four pigs at each level of ME intake). Nitrogen balances were determined over 7-d periods at approximately 25, 40, and 70 kg BW. The serial slaughter method was used to determine average PD over the entire BW range. Based on the N balances, PD increased up to intakes of 22.6, 21.3, and 25.1 MJ ME/d at 25, 40, and 70 kg BW, respectively. At higher ME intakes, PDmax was at least 156 g/d at 25 kg body weight; it was 149 g/d at 40 and 150 g/d at 70 kg BW. The serial slaughter technique showed a PDmax of 127 g/d at ME intakes above 22.5 MJ/d. At 25 kg BW, intakes of ME of approximately four times MEm are necessary to achieve PDmax. The results indicate that PDmax at 25 kg BW is at least as high as at 40 and 70 kg BW.