Mid- and late-pregnancy ewe shearing affects lamb neonatal reactivity and vigour

Abstract

Poor lamb survival is an important production and welfare issue, and the lamb must express complex behaviours to successfully transition to life ex-utero. Even under best management practices, sheep husbandry events, such as shearing, yarding and transport can be stressful for animals, and when they take place during pregnancy these stressors could possibly impact the neonate as well as the dam. This study examined the effects of some of the common stressors produced by shearing during pregnancy on neonatal lamb behaviour. Pregnant ewes were either subjected to shearing/cold stress or were handled (sham treatment), during mid- or late-pregnancy (four groups, n = 15 per group). Shorn ewes were wetted using sprinklers on three occasions the week following shearing to exacerbate the effect of cold. Neonatal lamb behaviour was assessed using a separation test and observance of lamb vigour related measures: Latency-to-Bleat; Latency-to-Stand; and Return-to-Ewe times, before and after a cold challenge at 4 °C of 1 h duration. Overall, lambs born to ewes shorn during pregnancy displayed higher Latency-to-Bleat than control lambs (P = 0.04). Mid-pregnancy shearing resulted in shorter Latency-to-Bleat than mid-pregnancy control treatment (P = 0.03). When shearing treatment was applied during late-pregnancy, lamb Return-to-Ewe time was higher than for lambs from ewes treated during mid-pregnancy which was in turn shorter than for control lambs (P = 0.006 & P = 0.04). Regardless of treatment groups, single lambs exhibited higher Latency-to-stand than twin lambs (P = 0.02). Lambs reacted faster and had shorter latencies to display behaviour after a cold challenge than before (P = 0.004). It seems that prenatal stress due to shearing of ewes during pregnancy adversely impacted neonatal behaviours but improved the behavioural responses of lambs after a cold stress challenge. Overall, shearing of ewes during pregnancy affected neonatal lamb behaviour and responses to cold challenge; however, the effects varied depending on litter size and timing of shearing. Differences between treatment groups and particularly between different timing of the stress treatment suggest there may be different mechanisms impacting on neonatal behaviour. Exposure to physiological stressors during pregnancy may improve resilience to these specific stressors. Further work is required to understand the underlying mechanisms leading to the observed changes in lamb behaviour.