Shearing during early mid-gestation improves umbilical blood flow and fetal size in ewes carrying multiples.

The objectives of this study were to evaluate the effects of shearing during early mid-gestation on umbilical blood flow (UBF), placental growth, fetal size, and lamb performance in Polypay ewes. Twenty-eight pregnant ewes were randomly assigned to either shorn (S) or sham-shorn control (CON) treatments on d 50 of gestation and stratified by fetal number as singleton (S: n = 4; CON: n = 4), twin (S: n = 5; CON: n = 5), or triplet (S: n = 5; CON: n = 5) pregnancies. Umbilical BF and fetal and placental measurements were obtained via Doppler ultrasonography every 10 d from d 50 to 110 of gestation. At parturition, lamb and placental weights were recorded, and cotyledonary tissue was collected. Data were analyzed for all pregnancies combined (ALL; singletons, twins, and triplets) and for multiple-bearing pregnancies (M; twins and triplets) using the MIXED procedure of SAS, with treatment, day of gestation, and their interaction included as fixed effects, and ewe included as a random effect. There was no treatment × day interaction for UBF in ALL or M (P=0.51). However, a main effect of treatment was observed (P<0.05), with UBF tending to be greater (P≤0.10) on d 90 and 100, and greater (P=0.03) on d 110, in S compared with CON ewes. Placentome size was not affected by treatment or treatment × day interactions in either analysis (P≥0.37). There was no treatment × day interaction or main effect of treatment for fetal biparietal distance (BP) in ALL (P≥0.11). In M pregnancies, BP was greater in fetuses from S ewes (main effect of treatment, P=0.01), tending to be greater on d 60 (P=0.07) and being greater on d 80, 90, and 110 (P≤0.05). Fetal abdominal distance was not affected by treatment or treatment×day interactions in ALL or M (P≥0.10). Lamb birth weight did not differ between treatments in ALL (P=0.22); however, lambs born from S ewes tended to be heavier at birth in M pregnancies (P=0.08) and tended to remain heavier at 60 d of age (P=0.10). Using DESeq2, we identified 680 DEGs between the S and CON groups (P<0.05 and |Log2FC| > 0.5). Among them, 566 genes were downregulated, and 114 were upregulated in the S group. These results demonstrate that shearing ewes on d 50 of gestation increases UBF and fetal skeletal growth, particularly in multiple-bearing pregnancies. The benefits of early mid-gestation shearing appear most relevant when fetal demand is high, suggesting this management practice may improve lamb growth and performance in prolific ewe flocks.