初产母猪妊娠期间不同饲喂水平下蛋白沉积情况的动态研究

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　　初产母猪妊娠期间不同饲喂水平下蛋白沉积情况的动态研究

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

　　初产妊娠母猪体蛋白沉积是其氨基酸需要量的主要决定因素。但是有关蛋白沉积的动态数据十分有限。本研究的主要目的在于测定2个饲喂水平下初产妊娠母猪体蛋白（妊娠相关组织和母体）的沉积状况。同时检测母猪妊娠期和哺乳期体重和背膘的变化情况。我们假定，由于胎儿需求量的增加，采食量对妊娠期母猪体蛋白沉积的影响将降低。

　　试验选用51头约克夏初产妊娠母猪（妊娠28±0.5d初始均重168.6±2.2kg，初始背膘厚16.9±0.8mm）。试验分为两组，妊娠期（33-112±0.5d）饲喂同一种日粮（代谢能3.30Mcal/kg，粗蛋白17.8%，SID赖氨酸0.82%），但是采食量不同，高采食量组为2.54kg/d，低采食量组为1.87kg/d。试验在5个不同时期（妊娠第38、52、66、87天，每期4天）观察母猪氮平衡状况，包括导尿管收集全部尿液，使用指示剂检测粪氮消化率。使用NRC（2012）妊娠母猪模型，基于产仔数（包括死胎）和平均初生重计算每头母猪每个时间段妊娠相关的蛋白沉积（胎儿、乳腺、子宫、胎盘和羊水）。母猪体蛋白沉积是根据整体蛋白沉积和妊娠相关蛋白沉积的差值计算的来。

　　在所有时间段内，高采食量组母猪的整体蛋白沉积和母猪本身体蛋白沉积均稳定高于低采食量组40.1±5.2g/d（P＜0.001）。不论采食量高低，母猪整体蛋白沉积随妊娠期延长显著增加（线性和二次线性，P＜0.02），而母猪本身蛋白沉积显著降低（三次线性，P＜0.01）。母猪哺乳期采食量和仔猪生长性能不受妊娠期采食量的影响。高采食量组初产母猪在妊娠期体重和背膘厚损失更多（P≤0.03）。

　　总之，妊娠期采食量对母猪整体蛋白沉积和母猪本身体蛋白沉积的影响一致。但是随着妊娠时间延长，母猪本身体蛋白沉积逐渐降低，这与NRC（2012）的报道相反，这对于使用析因法估计初产母猪妊娠后期氨基酸需要量有着重要的意义。

　　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。