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試驗一，選用2批共45頭初產(chǎn)母豬（妊娠39.4±1天，體重158.0±8.0kg），進行3期氮平衡試驗。母豬隨機分為4個日糧處理，分別提供最大蛋白質(zhì)沉積下SID賴氨酸日需要量（NRC2012）的60、70、80、90%，妊娠早期（第41-52天）、中期（第68-79天）、末期（第96-107天）SID賴氨酸日需要量分別為10.44、9.6、16.04g/d。日糧代謝能為3300kcal/kg，粗蛋白含量為11.6%，妊娠早期、中期飼喂量為2.13kg/d，妊娠后期飼喂量為2.53kg/d。每個試驗期為12天，7天試驗期，5天糞尿收集期，使用導尿管收集全部尿液，使用標記物測定粗蛋白消化率。通過NRC（2012）模型預測每個試驗期全體蛋白沉積所需要的SID賴氨酸量。通過日賴氨酸沉積量和SID賴氨酸攝入量計算每個處理中賴氨酸的沉積效率。檢測每個妊娠期體蛋白沉積、賴氨酸沉積、賴氨酸效率是否存在線性、二次線性效應。通過SID賴氨酸攝入量對體賴氨酸沉積量生成回歸方程，將截距設為0時，計算方程斜率k值。

在妊娠早期和中期，日糧SID賴氨酸和蘇氨酸對體蛋白沉積、賴氨酸沉積和蘇氨酸沉積沒有顯著影響。在妊娠后期，體蛋白沉積、賴氨酸沉積和蘇氨酸沉積線性提高（P＜0.001）。妊娠后期，SID賴氨酸和蘇氨酸k值均為0.54。妊娠早期和中期體蛋白沉積無變化，這可能是因為賴氨酸和蘇氨酸的過量攝入。最低日糧賴氨酸和蘇氨酸供應下，妊娠早期它們的沉積效率分別為0.49和0.32；妊娠中期沉積效率分別為0.61和0.52。

Two experiments were conducted to determine the efficiency of utilizing SID Lys and Thr for whole-body protein retention (kSIDLys and kSID Thr) in pregnant gilts. In Exp. 1, 45 gilts (158.0 ± 8.0 kg at day 39.4 ± 1 of gestation) in 2 groups were used in a 3-period nitrogen(N)-balance study. Gilts were assigned to 1 of 4 diets set to provide 60, 70, 80, and 90% of predicted daily SID Lys requirement for protein retention (NRC, 2012) in each of early (day 41 to 52, 10.44 g/d), mid- (day 68 to 79, 9.60 g/d), and late gestation (day 96 to 107, 16.04 g/d). Diets contained 3,300 kcal ME/kg and 11.6% CP; given at a rate of 2.13 kg/d in early and mid-gestation and at 2.53 kg/d during late gestation. The 12-d balance period (7-d adaptation; 5-d urine and fecal collection) was based on total urine collection using urinary catheters and determination of fecal N digestibility using indigestible marker. The SID Lys required for whole-body protein retention was estimated using the NRC (2012) model and the predicted Lys content of each gestation pool. Lysine efficiency at each diet Lys level was calculated as the ratio of daily Lys retention and SID Lys intake. The linear and quadratic response in whole-body N and Lys retention and Lys efficiency for each balance period was determined. The kSID Lys was determined from the slope generated by regressing whole-body Lys retention vs. SID Lys intake, with y-intercept set to 0. In Exp.2, 45 gilts (165.7 ± 13.6 kg at day 39.1 ± 2 of gestation) were assigned to 1 of 4 diets set to provide 60, 70, 80, and 90% of the predicted daily SID Thr requirement for protein retention in each of early (6.46 g/d), mid- (6.05 g/d), and late gestation (9.75 g/d). Animal management, N-balance procedure, data collection and calculation, and statistical analyses were patterned from Exp.1. In early and mid-gestation, whole-body N retention, as well as Lys and Thr retention, was not affected by the dietary SID Lys and Thr. In late gestation, there was a linear increase (P < 0.001) in whole-body N, Lys and Thr retention. The kSID Lys and kSIDThr in late gestation were determined to be 0.54. The lack of response in whole-body protein retention in early and mid-gestation may in partly reflect excess Lys and Thr intake. Lysine and Thr efficiency calculated at the lowest dietary Lys and Thr was 0.49 and 0.32 in early gestation and 0.61 and 0.52 in mid-gestation, respectively. Based on the available evidence, kSIDLys and kSIDThr do not appear to be constant throughout gestation.

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