49 The Effect of Increasing Standardized Ileal Digestible Methionine Intake During Lactation on Whole-Body Nitrogen Utilization of Primiparous Sows

Abstract

Abstract Seventy-five primiparous Yorkshire × Landrace and Yorkshire sows were used to determine the effect of increasing dietary standardized ileal digestible (SID) methionine (Met) intake on whole-body nitrogen (N) utilization during lactation. Upon farrowing (190.2 ± 18.0kg initial body weight), sows were assigned to 1 of 7 dietary SID Met levels (n = ~10), ranging from 70% to 130% of estimated SID Met requirements (0.182 to 0.338% SID Met) via the addition of DL-Met. All other indispensable amino acids were supplied above estimated requirements (1.19% SID lysine, 19.74% crude protein) and additional cysteine was supplied to minimize Met utilization for transsulfuration. Litters were standardized to 13 ± 2 piglets within 48 hours of birth and feed was offered according to a standard feeding curve (NRC, 2012). The N balance periods were between days 5 to 9 (early; N1) and 17 to 21 (Peak; N2) of lactation where total urine was collected via urinary catheters and feces was grab-sampled; titanium dioxide was used as an indigestible marker for determining apparent total tract N digestibility. In N1 and N2, 5.22 and 6.87 kg/d of experimental diet was offered in three equal meals at 0830, 1200, and 1530 h to each sow. Milk N output (g/d) was calculated using estimated milk yield based on litter growth rate and size and analyzed milk N concentration. Contrast statements were used to assess linear and quadratic effects of dietary SID Met level. During N1, N intake increased and then decreased when dietary SID Met content surpassed 0.286% (quadratic; P < 0.05). Similar relationships were observed for total N excretion (urine + fecal N; P < 0.05) resulting in no SID Met effect on N retention (77.1 ± 6.6, -12.5 ± 10.4, and 89.5 ± 8.9 g/d for total, maternal, and true milk protein N retention, respectively) or apparent N utilization efficiency (N retention/N intake×100; 53.2 ± 3.4%). During N2, as SID Met increased, N intake tended to increase (205.5 to 210.2 ± 5.7g/d; linear; P = 0.078), total N excretion tended to decrease (87.3 to 78.7 ± 6.2 g/d; linear; P = 0.087), and total N retention increased (117.9 to 131.4 ± 8.0g/d; linear; P < 0.05). True milk protein N output increased with SID Met (100.3 to 112.5 ± 8.1 g/d; linear; P < 0.05) and maternal N retention decreased and then increased when dietary SID Met content surpassed 0.260% (quadratic; P < 0.05). Apparent N utilization efficiency increased with increasing dietary SID Met (57.5 to 62.5 ± 1.2%; linear; P< 0.05). Therefore, in early lactation, SID Met intake had minimal effects on N utilization, indicating that the requirement for lactating primiparous sows may be equal to or less than 0.182% SID Met. During peak lactation, the supply of SID Met needed to maximize true milk protein N and apparent N utilization efficiency may be greater than 0.338%, which does not take into consideration the non-protein partitioning of dietary Met.