van der Waaij E H, Hazeleger W, Soede N M, Laurenssen B F A, Kemp B
Adaptation Physiology Group, Wageningen University, 6700 AH, Wageningen, the Netherlands.
J Anim Sci. 2010 Aug;88(8):2611-9. doi: 10.2527/jas.2009-2561. Epub 2010 Apr 9.
Selection for litter size may result in an increase in uterine crowding due to a faster increase in ovulation rate than in litter size. Increased ovulation rate does not result in a proportionally increased number of piglets born alive. In this study, the effect of ovulation rate on vitality characteristics of fetal-placental units at d 40 of pregnancy was investigated. For this, 43 Large White gilts were treated with hormones to induce superovulation. Average ovulation rate was 45.16 +/- 13.22; average number of vital fetuses at d 40 of pregnancy was 17.09 +/- 3.61 that weighed 11.26 +/- 1.99 g; their placenta weighed 31.88 +/- 14.79 g; and they occupied 11.69 +/- 4.90 cm of the uterus. Loss in oocytes (i.e., that did not result in a vital fetus at d 40) increased with increasing ovulation rate and occurred before (early mortality; P = 0.0003) and after implantation (late mortality, i.e., traces visible at d 40; P < 0.0001). With respect to the vital fetuses, increased ovulation rate resulted in decreased fetal (P = 0.0008) and placental weight (P = 0.0008) and decreased length of the area in the uterus that was occupied by the placenta (P = 0.0011). Strong correlations existed between placental and fetal weight [0.68; 95% confidence interval (CI) = 0.64 to 0.72], and placental weight and length (0.78; 95% CI = 0.74 to 0.82). Fetal-placental characteristics were weakly correlated to distance to the implantation sites of neighboring fetuses, a measure of crowdedness [-0.002 (95% CI = -0.042 to 0.038) with fetal weight to 0.16 (95% CI = 0.12 to 0.20) with placental length]. Increased ovulation rates, but more specifically increased late mortality rates, have negative effects on the remaining vital fetuses with respect to the fetal (P = 0.0085) and placental weight (P < 0.0001) and length of the implantation site (P = 0.0016). The most extreme effect was on placental weight, in which a uterus with <10 cases of late mortality was on average 25% greater than placental weight in a uterus with >18 cases of late mortality (P < 0.0001). Furthermore, increased ovulation rates resulted in decreased within litter variation for fetal (P = 0.0018) and placental weight (P = 0.0084). At increased ovulation rates, the number of live fetuses remained similar, but placental development is impaired and the growth of the fetus is retarded compared with reduced ovulation rate, with effects likely lasting into adult life.
由于排卵率的增长速度快于窝产仔数，对窝产仔数进行选择可能会导致子宫拥挤加剧。排卵率增加并不会使出生存活仔猪数量按比例增加。在本研究中，调查了妊娠第40天时排卵率对胎儿 - 胎盘单位活力特征的影响。为此，对43头大白母猪进行激素处理以诱导超排卵。平均排卵率为45.16±13.22；妊娠第40天时存活胎儿的平均数量为17.09±3.61头，体重为11.26±1.99克；其胎盘重31.88±14.79克；它们占据子宫11.69±4.90厘米。随着排卵率的增加，未发育成妊娠第40天时存活胎儿的卵母细胞损失增加，且发生在植入前（早期死亡；P = 0.0003）和植入后（晚期死亡，即在第40天时可见痕迹；P < 0.0001）。对于存活胎儿，排卵率增加导致胎儿（P = 0.0008）和胎盘重量（P = 0.0008）下降，以及胎盘在子宫内占据区域的长度缩短（P = 0.0011）。胎盘重量与胎儿体重之间存在强相关性[0.68；95%置信区间（CI）= 0.64至0.72]，胎盘重量与长度之间也存在强相关性（0.78；95%CI = 0.74至0.82）。胎儿 - 胎盘特征与相邻胎儿植入部位的距离（衡量拥挤程度）之间的相关性较弱，胎儿体重的相关性为 -0.002（95%CI = -0.042至0.038），胎盘长度的相关性为0.16（95%CI = 0.12至0.20）。排卵率增加，更具体地说是晚期死亡率增加，对剩余存活胎儿的胎儿（P = 0.0085）和胎盘重量（P < 0.0001）以及植入部位长度（P = 0.0016）有负面影响。最极端的影响是对胎盘重量，晚期死亡率<10例的子宫中胎盘重量平均比晚期死亡率>18例的子宫大25%（P < 0.0001）。此外，排卵率增加导致窝内胎儿（P = 0.0018）和胎盘重量（P = 0.0084）的变异性降低。在排卵率增加时，存活胎儿数量保持相似，但与排卵率降低相比，胎盘发育受损且胎儿生长受阻，这种影响可能持续到成年期。
