Shearing during the latter half of pregnancy is a common practice to improve flock health and productivity. Previous studies have demonstrated that shearing pregnant ewes at mid or late pregnancy is associated with an increase in lamb birth weight. In the present study, we used singleton Polypay × Dorset pregnant sheep, to investigate the potential roles of placental function and changes in maternal metabolism in underlying this increased birth weight response. Two groups were randomly established and blocked at enrollment by animal BW, body condition score and subcutaneous adipose tissue depth. The groups were shorn (SH; n = 18) or not (C; n = 20) at gestational day (GD) 107 ± 1 (mean ± SEM). Weekly maternal plasma samples were collected between shearing and birth, but only six samples were assayed for progesterone, pregnancy-associated glycoproteins (PAG1), glucose and non-esterified fatty acids (NEFAs). At birth, sex, birth weight, and newborn body mass index (BMI) were recorded. Maternal BW during mid- to late-pregnancy was similar between groups. Shearing resulted in increased lamb birth weight and BMI (P < 0.05) regardless of fetal sex but did not affect the maternal concentration of PAG1 or progesterone from GDs 100 to 142. After shearing (GD100) and up to lambing, shorn females had higher circulating glucose concentrations (P < 0.05), but not NEFA, compared to the control group. Maternal circulating PAG1, progesterone, glucose or NEFA concentration across pregnancy did not differ according to lamb sex. Across pregnancy, birth weight was positively associated with PAG1 (P < 0.001), but not with progesterone concentrations. In conclusion, weight and BMI at birth were higher in both sexes upon shearing in singleton pregnancies. Despite PAG1 being associated with birth weight, late-pregnancy shearing did not alter the placental endocrine response. Whether other placental factors are altered upon shearing and may influence the increase in birth weight and BMI remain to be investigated.

中文翻译：

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妊娠后期的剪切增加了出生时的体形，但并未改变绵羊的胎盘内分泌反应。

怀孕后半期的剪毛是提高鸡群健康和生产力的常见做法。先前的研究表明，在妊娠中期或晚期剪羊毛会导致羔羊出生体重增加。在本研究中，我们使用单胎Polypay×Dorset怀孕绵羊来研究胎盘功能和母体代谢变化在这种增加的出生体重反应中的潜在作用。随机分为两组，并根据动物体重，身体状况评分和皮下脂肪组织深度阻止其入组。在妊娠日（GD）107±1（平均±SEM）时，这些组是剪（SH； n = 18）或不是（C； n = 20）。在剪切和分娩之间每周收集一次母体血浆样品，但仅分析了六个样品中的孕酮，妊娠相关糖蛋白（PAG1），葡萄糖和非酯化脂肪酸（NEFA）。记录出生时的性别，出生体重和新生儿体重指数（BMI）。两组孕妇之间的孕产妇体重相似。剪切导致羔羊出生体重和BMI升高（P <0.05），无论胎儿性别如何，但均未影响PAG1或孕激素从GDs 100至142的孕产妇浓度。经过剪切（GD100）直至产羔，,女性的循环更高与对照组相比，葡萄糖浓度（P <0.05），但不是NEFA。产妇在妊娠期间循环的PAG1，孕酮，葡萄糖或NEFA的浓度根据羔羊性别而无差异。在整个怀孕期间，出生体重与PAG1呈正相关（P <0.001），但与孕激素浓度无关。结论，单胎妊娠时，出生时的体重和BMI在两性中均较高。尽管PAG1与出生体重有关，但妊娠后期的剪力并未改变胎盘的内分泌反应。其他胎盘因素是否会在剪切时发生改变，并可能影响出生体重和BMI的增加，尚待研究。