THE EFFECT OF BODY-WEIGHT ON THE UPPER LIMIT TO PROTEIN DEPOSITION INA DEFINED POPULATION OF GROWING GILTS

In a stress-free environment and given adequate intakes of essential n utrients, protein deposition (PD) in growing pigs is determined by eit her energy intake or the genetically determined upper Limit to body pr otein deposition (PDmax). In this experiment, the effect of metaboliza ble 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 limit ing 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 P D over the entire BW range. Based on the N balances, PD increased up t o intakes of 22.6, 21.3, and 25.1 MJ ME/d at 25, 40, and 70 kg BW, res pectively. At higher ME intakes, PDmax was at least 156 g/d at 25 kg b ody weight; it was 149 g/d at 40 and 150 g/d at 70 kg BW. The serial s laughter 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 n ecessary to achieve PDmax. The results indicate that PDmax at 25 kg BW is at least as high as at 40 and 70 kg BW.