215 Optimizing the Standardized Ileal Digestible Lys-To-Net Energy Ratio for Nitrogen Utilization of Sows Throughout a 24-Day Lactation Period

Abstract

Abstract Fifty multiparous sows (average parity 3.7±0.9 and initial BW 245.6±32.5 kg) were used to evaluate the effects of dietary standardized ileal digestible (SID) Lys-to-net energy (NE) ratios on nitrogen utilization throughout a 24-day lactation period. Sows were randomly assigned to one of five isoenergetic feeding programs that provided equally spaced and increasing Lys-to-NE ratios between 2.79 and 5.50 g SID Lys/Mcal NE. The feeding programs were generated by blending the two extreme diets in varying proportions using a precision feeding system and were provided to sows immediately after farrowing (d1) and until weaning at d 24 ± 1. At farrowing, litters were standardized to 12 piglets. Three nitrogen balances were conducted from d 4 to 7±1 (NB1), 12 to 15 ± 1 (NB2), and 20 to 23 ± 1 (NB3) using total urine collection and fecal grab sampling. Contrast statements were used to determine linear and quadratic effects of increasing Lys-to-NE ratios. Linear (LBL) and quadratic (QBL) broken-line and polynomial quadratic (QPM) models were used to determine the optimum dietary Lys-to-NE ratios for N retention. The Bayesian information criterion was used to assess best fit. Feeding program did not influence sow ADFI (5.96 ± 0.19 kg/d), BW change (-5.4 ± 4.1 kg) or change in backfat thickness (-2.0 ± 1.1 mm) over the entire 24-d lactation period, but piglet ADG increased with dietary Lys-to-NE ratio (linear; P < 0.05). Sow N intake increased with dietary Lys-to-NE ratio in NB2 and NB3 (linear; P< 0.001). Nitrogen retention (N intake – N output in urine and feces) increased with dietary Lys-to-NE ratio in all NB (linear; P = 0.05, P < 0.001, and P < 0.001 for NB1 -to 3, respectively). The QPM showed an inflection point at 3.75 g Lys/Mcal NE during NB1 and the QBL model showed break points at 2.87 and 4.83 g Lys/Mcal NE in NB2 and NB3, respectively. Nitrogen retention in milk increased with dietary Lys-to-NE ratio only in NB1 (linear; P < 0.05) and the QPM showed inflection points at 4.31, 4.37, and 4.90 g Lys/Mcal NE for NB1-to-3, respectively. Maternal nitrogen retention (N intake – N output in urine, feces, and milk) decreased and then increased in NB1 (quadratic; P < 0.01) and increased in NB2 and NB3 (linear; P < 0.01) with dietary Lys-to-NE ratio. The QPM showed inflection points at 4.01 and 3.01 g Lys/Mcal NE for NB1 and NB2, respectively, and the QBL model showed a breakpoint at 4.83 g Lys/Mcal NE for NB3. To optimize N retention, feeding programs with a Lys-to-NE ratio between 3.75 and 4.31, 2.87 and 4.37, and 4.83 and 4.90 g SID Lys/Mcal NE should be considered during early, mid, and peak lactation, respectively. Therefore, precision feeding programs can be developed to match the ideal SID Lys-to-NE ratio more closely at different stages of lactation to improve sow performance and reduce nitrogen excretion to the environment.