Effects of sex and gonadectomy on the growth and development of Southdown × Romney cross lambs. Part I. Effects on live–weight growth and components of live weight

Abstract

The influence of sex and gonadectomy on liveweight growth and its components was examined in a comparative slaughter experiment using Southdown – Romney cross lambs run under New Zealand pastoral feeding conditions.Twenty ram lambs were castrated and 20 ewe lambs spayed at docking, at approximately 4 weeks of age. Ten ram and 10 ewe lambs were killed at this age and 5 lambs from each of the four ‘sexes’ (entire and gonadectomized, male and female) were killed 4, 8,12 and 24 weeks after docking.Live-weight gain was higher for males than females and higher for entire than gonadectomized lambs, with some evidence of a greater depression in growth associated with castration than spaying. Effects on carcass weight followed those on live weight; weights for entire rams, wethers, entire and spayed ewes were 16.92, 14.72, 14.02 and 12.46 kg. respectively at approximately 7 months of age.