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Impact of reduced crude protein diets on lactating sow nitrogen utilization and piglet performance
Forty lactating multiparous Yorkshire sows were used to determine if reducing dietary crude protein (CP) and supplementing with crystalline amino acids (CAA) increases piglet performance and maternal N utilization during early and peak lactation. Sows were assigned to 1 of 4 diets: [1] 16.0% CP (as-fed; analyzed contents; HCP); [2] 15.7% CP (MHCP); [3] 14.3% CP (MLCP); [4] 13.2% CP (LCP); diet HCP was formulated using soybean meal and corn as the only Lys sources. Across diets standardized ileal digestible (SID) content of Lys was 0.86%, based on analyzed content and estimated SID. Other essential AA were included to exceed requirements. Sow and piglet BW were measured on d 1, 3, 7, 14, 18 and 21 of lactation. Sow N balances were conducted between d 3 and 7 (early) and d 14 and 18 (peak). Milk N output was calculated from estimated milk yield and analyzed true protein concentration. Sow BW change and litter ADG did not differ between diets (mean: −248 and 2259 g/d, respectively), nor did sow average daily DM intake (mean: 4.05 and 6.12 kg/d; early and peak lactation, respectively) or fecal N digestibility (mean: 88.6%). Nitrogen intake decreased as dietary CP decreased (114.3, 106.0, 107.4, and 99.0±5.29 g/d and 169.5, 168.3, 161.2, and 145.1±5.29 g/d for HCP, MHCP, MLCP, and LCP in early and peak lactation, respectively; Linear (L) P<0.05 and quadratic (Q) effects of diet CP content: P>0.10). In early lactation, N retention (N intake – N excretion with feces and urine) and milk N output were not affected by diet (P>0.10), and N retained as percentage of N intake tended to increase as dietary CP decreased (L: P=0.09). In peak lactation, N retention decreased (122.5, 123.8, 121.2, and 109.0±4.88 g/d for HCP, MHCP, MLCP, and LCP, respectively; L: P<0.05 and Q: P=0.16), N retained as percentage of intake tended to increase (L: P=0.11), and estimated efficiency of using retained N for milk N output increased (51.0, 55.2, 57.1, and 66.3±8.43 % for HCP, MHCP, MLCP, and LCP, respectively; L: P<0.05). Feeding lactating diets reduced in CP from 16.0 to 14.3% with CAA inclusion as partial replacement for limiting AA maintains piglet performance and improves N utilization efficiency, but at the lowest dietary CP N retention during peak lactation was reduced.
Keywords: amino acid intake, lactating sows, nitrogen retention