Wilson M E, Biensen N J, Ford S P
Department of Animal Science, Iowa State University, Ames 50011, USA.
J Anim Sci. 1999 Jul;77(7):1654-8. doi: 10.2527/1999.7771654x.
Chinese Meishan pigs produce three to five more pigs per litter than less-prolific U.S. or European pig breeds as a result of a markedly decreased placental size and an increased pig weight: placental weight ratio (placental efficiency). We hypothesized that as a result of their intense selection for prolificacy, the Chinese had indirectly selected for a smaller, more efficient placenta in the Meishan breed. The goals of this study were to determine whether 1) significant variation in placental size and efficiency existed within our population of purebred Yorkshire pigs and 2) selection of pigs (boars and gilts) based on clear differences in placental size and efficiency would affect litter size. There was significant (approximately threefold) variation in placental efficiency in our herd of Yorkshire pigs, and marked (approximately twofold) variation existed within individual litters. We then selected pigs (boars and gilts) that had either a higher (A Group) or lower (B Group) than average placental efficiency. Although the birth weights of selected A Group pigs were similar to those of the B Group pigs, they had markedly smaller placentae. Males from each group (A or B) were bred to the females of the same group, and farrowing data were collected from parities 1 and 2. In both parities, A Group females farrowed more live pigs per litter than did B Group females (12.5 +/- .7 vs 9.6 +/- .5, P < .05). Although A Group pigs were on average approximately 20% lighter than B group pigs (1.2 +/- .1 vs 1.5 +/- .1 kg, P < .05), their placentae were approximately 40% lighter (250 +/- 10 vs 347 +/- 15 g, P < .01), resulting in a marked increase in placental efficiency. The results of this study suggest that selection on placental size and efficiency may provide a valuable tool for optimizing litter size in commercially important pig breeds.
中国梅山猪每窝产仔数比繁殖力较低的美国或欧洲猪种多三到五头，这是因为胎盘大小显著减小且仔猪体重与胎盘重量之比（胎盘效率）增加。我们推测，由于对繁殖力进行了高强度选择，中国人间接选择了梅山猪品种中更小、更高效的胎盘。本研究的目的是确定：1）在我们的纯种约克夏猪群体中，胎盘大小和效率是否存在显著差异；2）根据胎盘大小和效率的明显差异选择猪（公猪和后备母猪）是否会影响产仔数。在我们的约克夏猪群中，胎盘效率存在显著（约三倍）差异，且在个体窝中存在明显（约两倍）差异。然后，我们选择了胎盘效率高于（A组）或低于（B组）平均水平的猪（公猪和后备母猪）。虽然所选A组猪的出生体重与B组猪相似，但它们的胎盘明显更小。每组（A或B）的公猪与同组的母猪交配，并收集第1胎和第2胎的产仔数据。在两胎中，A组母猪每窝产活仔数均多于B组母猪（12.5±0.7对9.6±0.5，P<0.05）。虽然A组猪平均比B组猪轻约20%（1.2±0.1对1.5±0.1千克，P<0.05），但其胎盘轻约40%（250±10对347±15克，P<0.01），导致胎盘效率显著提高。本研究结果表明，根据胎盘大小和效率进行选择可能为优化商业上重要的猪品种的产仔数提供一种有价值的工具。
