Shearing Effects during Pregnancy on Birthweights and Survivability of Lambs

The increased birth weights of lambs of shorn ewes were hypothesized to be due to cold stress. Studies performed in warmer climates also report increased birth weights and increased survivability in lambs born from shorn ewes. To our knowledge, the effects of shearing pregnant ewes on lamb birth weight and survivability has not been analyzed in the USA. For this pilot study, multiparous pregnant whiteface ewes were randomly selected from the USDA Sheep Experiment Station (Dubois, ID). They were randomly divided into two treatments groups: shorn (n = 15) and unshorn (n = 18). Ewes were grazed on winter rangelands from approximately d 30 to 65 of gestation, then transitioned to a feedlot environment thereafter. Complete shearing was performed to the shorn group at approximately d 105 of gestation. Ewes gave birth to singletons (n = 7), twins (n = 21), and triplets (n = 5). Birth weights were analyzed using the PROC GLM procedure of SAS. Offspring number was included in the model as a covariate. Survivability of lambs was measured at approximately d 35 of age and was analyzed using the PROC GLIMIX procedure of SAS. Lambs born from the shorn group tended (P = 0.08) to be heavier than the unshorn group (5.90 vs. 5.52 ± 0.16 kg). While not significant (P = 0.42), survivability of lambs born from shorn ewes were numerically greater than unshorn ewes. The majority of previous studies report positive effects of shearing during pregnancy in lamb birth weights and survivability. While increasing birth weights in singleton pregnancies could be perceived as detrimental, increasing birth weights in twin and triplet pregnancies could be of great benefit, as this could be the reason for the reported increase in survival rates to weaning. Our results suggest that the positive effects of shearing during pregnancy observed in other parts of the world can be mimicked in the USA. Further investigations with a greater number of animals and different pregnancy stages are necessary in the future to confirm the positive effects presented in this abstract. Studies analyzing the effects of shearing during pregnancy in reproductive traits such as umbilical blood flow and/or placental macro- and microscopic characteristics need to be further analyzed. If increased survival rates in twins and triplets are confirmed in future studies, the labor and economic benefits for producers could be very significant.