Dietary protein requirement of hyper-prolific sows in late gestation

This study aimed to determine the protein requirement of hyper-prolific sows in late gestation. Forty-eight multiparous sows were assigned to one of six dietary treatments according to body weight (BW; 287 ± 5 kg) on d 84 of gestation and parity (3.8 ± 0.1) and fed 3.3 kg/d from d 84 to 108 of gestation. Five dietary treatments had increasing concentrations of dietary protein [expressed as standardized ileal digestible (SID) lysine (Lys); 3.05 to 6.90 g/kg]. The sixth treatment (high-cAA) had reduced crude protein (CP) relative to Lys concentration and was supplemented with crystalline amino acids (AA), so that the concentration of the supplemented AA matched that of the diet containing 6.90 g/kg of SID Lys and the remaining essential AA matched that of the diet containing 3.05 g/kg of SID Lys. Sow BW and backfat thickness (BF) were measured and blood was sampled on d 84, 96 and 108 of gestation and weekly during lactation. Deuterium oxide was injected on d 84 and 108 of gestation and on d 3 and 28 of lactation to estimate sow body composition. A nitrogen (N) balance was conducted on d 107 of gestation. At the onset of farrowing, colostrum and blood were sampled from the sows and number and birth time of live- and stillborn piglets, and birth weight of liveborn were recorded. Piglets were weighed and colostrum sampled at 12, 24, and 36 h after the onset of farrowing, and thereafter weekly weighing and milk sampling during lactation. From d 84 to 108 of gestation sow BW increased with SID Lys until reaching a plateau at 5.63 g/kg of SID Lys (P = 0.02) and sow BF had a polynomial relationship with SID Lys, which peaked at 4.85 g/kg of SID Lys (P = 0.04). On d 107 of gestation, N retention and utilization increased linearly with SID Lys and reached plateaus at 5.60 (P < 0.001) and 5.07 g/kg of SID Lys (P < 0.01), respectively. Reproductive parameters were not affected by dietary treatments and there were no indications of carry-over effects to lactational performance. During the treatment period, sows fed the high-cAA diet had higher BW (P < 0.01) and body protein (P = 0.02) gain than sows fed 3.05 g/kg of SID Lys and on d 107 of gestation they had reduced excretion of urea and N in urine (P < 0.001 for both) relative to sows fed 6.90 g/kg of SID Lys. Also, compared to any other treatment, the plasma concentration of sows fed the high-cAA diet gradually decreased during the treatment period (P < 0.01), indicating reduced AA oxidation. In conclusion, a SID Lys concentration of 4.85 to 5.07 g/kg (16.0 to 16.7 g/d) from d 84 to 108 of gestation ensures optimal utilization of N and maximizes BF gain in hyper-prolific sows. Piglet and litter birth weight and sow milk yield were unaffected by dietary concentration of SID Lys. Feeding late gestating sows diets with reduced CP relative to Lys and supplemented with crystalline AA, improved N balance, with no indications of impaired reproductive and subsequent lactational performance or reduced maternal gain, suggesting that the AA composition of the high-cAA diet met the sows’ requirement for essential AA.