初產母豬妊娠期間不同飼喂水平下蛋白沉積情況的動態研究

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　　初產母豬妊娠期間不同飼喂水平下蛋白沉積情況的動態研究

　　E. G. Miller, C. L. L. Levesque, N. Trottier和C. F. M. de Lange

　　初產妊娠母豬體蛋白沉積是其氨基酸需要量的主要決定因素。但是有關蛋白沉積的動態數據十分有限。本研究的主要目的在于測定2個飼喂水平下初產妊娠母豬體蛋白（妊娠相關組織和母體）的沉積狀況。同時檢測母豬妊娠期和哺乳期體重和背膘的變化情況。我們假定，由于胎兒需求量的增加，采食量對妊娠期母豬體蛋白沉積的影響將降低。

　　試驗選用51頭約克夏初產妊娠母豬（妊娠28±0.5d初始均重168.6±2.2kg，初始背膘厚16.9±0.8mm）。試驗分為兩組，妊娠期（33-112±0.5d）飼喂同一種日糧（代謝能3.30Mcal/kg，粗蛋白17.8%，SID賴氨酸0.82%），但是采食量不同，高采食量組為2.54kg/d，低采食量組為1.87kg/d。試驗在5個不同時期（妊娠第38、52、66、87天，每期4天）觀察母豬氮平衡狀況，包括導尿管收集全部尿液，使用指示劑檢測糞氮消化率。使用NRC（2012）妊娠母豬模型，基于產仔數（包括死胎）和平均初生重計算每頭母豬每個時間段妊娠相關的蛋白沉積（胎兒、乳腺、子宮、胎盤和羊水）。母豬體蛋白沉積是根據整體蛋白沉積和妊娠相關蛋白沉積的差值計算的來。

　　在所有時間段內，高采食量組母豬的整體蛋白沉積和母豬本身體蛋白沉積均穩定高于低采食量組40.1±5.2g/d（P＜0.001）。不論采食量高低，母豬整體蛋白沉積隨妊娠期延長顯著增加（線性和二次線性，P＜0.02），而母豬本身蛋白沉積顯著降低（三次線性，P＜0.01）。母豬哺乳期采食量和仔豬生長性能不受妊娠期采食量的影響。高采食量組初產母豬在妊娠期體重和背膘厚損失更多（P≤0.03）。

　　總之，妊娠期采食量對母豬整體蛋白沉積和母豬本身體蛋白沉積的影響一致。但是隨著妊娠時間延長，母豬本身體蛋白沉積逐漸降低，這與NRC（2012）的報道相反，這對于使用析因法估計初產母豬妊娠后期氨基酸需要量有著重要的意義。

　　Dynamics of nitrogen retention in gestating gilts at two feeding levels

　　E. G. Miller, C. L. L. Levesque, N. Trottier and C. F. M. de Lange

　　Whole-body protein deposition (Pd) is a main determinant of AA requirements of gestating gilts; however, data on the dynamics of Pd is limited. The main objective of this study was to measure whole-body Pd (pregnancy-associated and maternal) during gestation in gilts at 2 feeding levels. Changes in BW and backfat (BF) throughout gestation and subsequent lactation performance were also evaluated. We hypothesized that the effect of feed intake on maternal Pd decreases toward the end of gestation due to increased fetal nutrient demands. Fifty-one pregnant Yorkshire gilts (initial BW and BF at d 28 ± 0.5 of gestation were168.6 ± 2.2 kg and 16.9 ± 0.8 mm, respectively) were used. Gilts were assigned to 1 of 2 feeding levels (high feeding level and low feeding level; 2.54 and 1.87 kg/d, respectively) of the same diet (3.30 Mcal ME/kg, 17.8% CP, 0.82% standard ileal digestible Lys) from d 33 to 112 ± 0.5 of gestation. Nitrogen balance observations (based on total urine collection with urinary catheters and determination of fecal N digestibility using an indigestible marker) were made at 5 distinct time periods, each 4 d in length, starting at d 38, 52, 66, 87, and 108 ± 0.5 of gestation. Pregnancy-associated Pd (fetus, mammary gland,uterus, and placenta and fluids) was calculated for each gilt and N balance period using the NRC (2012) gestating sow model, based on actual litter size (including stillborns) and mean piglet birth weight. Maternal Pd was calculated as the difference between whole-body Pd and pregnancy-associated Pd. Across all N balance periods, whole-body and maternal Pd were consistently 40.1 ± 5.2 g/dgreater (P < 0.001) for the high feeding level compared with the low feeding level. At both feeding levels, whole-body Pd increased (linear and quadratic, P< 0.020) with day of gestation and maternal Pd decreased (cubic, P <0.010) with day of gestation. During lactation, maternal voluntary feed intake and litter performance were not affected by gestation feeding level. Gilts on the high feeding level lost more BW and BF during lactation (P ≤ 0.030). In summary, the effect of feeding level on whole-body and maternal Pd was constant throughout gestation. However, the gradual decline in maternal Pd withday of gestation is in contrast to that reported by the NRC (2012) and has important implications for the factorial estimation of AA requirements of gestating gilts toward the end of gestation。