Narrative Review of Production Impacts of Pregnancy Shearing in Pasture-Based Systems

This review used a qualitive approach to help further understand the benefits of pregnancy shearing and its potential mechanisms. A recent meta-analysis showed that pregnancy shearing increased lamb birth weight when conducted between days 42 and 100 of gestation but not after day 100; however, there was no effect on lamb weaning weight. Factors identified as potential mechanisms for the lamb birth weight response include comb type, gestation length, ewe pregnancy nutrition and feed intake, changes in ewe hormones and metabolites and altered placental development. There was, however, no single consistent parameter identified for the birth weight effect and more research is required. Shearing can potentially increase lamb survival, thermoregulatory capability and improve behaviour and ewe milk production but, again, further research is also required to confirm these. In conclusion, to maximise the chance of a birth weight response, farmers should focus on twin-bearing ewes of adequate body condition, shear with a comb that leaves a greater stubble depth and ensure ewes are offered at least pregnancy maintenance feeding levels.