The effect of mid-pregnancy stressors on twin-lamb live weight and body dimensions at birth

This study was conducted to determine the effect of crutching, simulated shearing and conventional shearing in mid-pregnancy on maternal plasma cortisol levels and lamb live weight and body dimensions at birth. Twin-bearing Romney ewes (n = 96) were subjected to one of four treatments (control, crutched, sham shorn and shorn) on day 80 of pregnancy. Ewes were maintained as a single flock throughout pregnancy under commercial farming conditions. Within 12 h of birth the lambs were weighed and their body dimensions recorded. Lambs born to ewes shorn in mid-pregnancy were heavier (P < 0.05) at birth than lambs born to control or sham-shorn ewes by 300 and 400 g (7 and 10%) respectively. The birth weight of lambs born to crutched and control ewes did not differ. Shearing and crutching produced a greater integrated cortisol response than sham-shearing (P < 0.05). The failure of crutching to increase lamb birth weight suggests that the acute stress caused by shearing does not result in increased lamb birth weights.