Optimal protein concentration in diets for sows during the transition period

The aim of the present study was to determine the optimal concentration of dietary protein required in transition diets for multiparous sows that enhance the farrowing process, colostrum production, and subsequent lactation performance. Forty-eight multiparous sows were allotted to one of six dietary treatments according to body weight (290 ± 3 kg) and parity (3.8 ± 0.2) from day 108 of gestation until 24 h after the onset of farrowing. The diets were isoenergetic and contained increasing concentrations of dietary protein (expressed as standardized ileal digestible [SID] Lys) and were supplied at a daily feed supply of 3.8 kg. On day 108 of gestation and days 2, 7, 14, 21, and 28 of lactation, body weight, and back fat thickness were recorded, and blood was sampled on day 108 of gestation, at the onset of farrowing, and days 3, 10, 17, and 24 of lactation from the sows for analysis of plasma metabolites. On day 115 of gestation, urine, and feces were collected for nitrogen (N) balance. The number of liveborn and stillborn piglets and time of birth were recorded and blood from every fourth piglet was sampled at birth for blood gas analysis. Piglets were weighed individually from birth until weaning, to estimate the colostrum and milk yield of the sows. Colostrum and milk samples were collected, and their compositions were determined. On days 3 and 28 of lactation, sows were injected with deuterium oxide to estimate body composition. The N utilization was maximized when the concentration of SID Lys in the transition diet was 6.06 g/kg (P < 0.01). When urinary concentrations of urea were expressed relative to creatinine, the relative concentration of urea remained low until a dietary concentration of 6.08 g SID Lys/kg, above which the relative concentration of urea increased (P < 0.01). Stillbirth rate increased linearly with increasing SID Lys concentration in the transition diet (P < 0.001), thus the concentration of SID Lys should be kept as low as possible without impairing sow performance excessively. A carry-over effect on milk yield was observed, showing that a dietary SID Lys concentration of 5.79 g/kg during transition optimized milk production at an average yield of 13.5 kg/d (P = 0.04). Increasing loss of body fat in lactation was observed with increasing SID Lys concentration in the transition diet (P = 0.03). In conclusion, the transition diet of multiparous sows should contain 5.79 g SID Lys/kg when fed 3.8 kg/d (13.0 MJ ME/kg), for a total SID Lys intake of 22 g/d.