Studies in pasture management for the breeding ewe. I. Effects on ewe liveweights, incidence of pregnancy toxaemia, lamb birth weights, and neo-natal mortality

Abstract

Breeding ewes were run under three systems of pasture management on sown pastures (based on subterranean clover) at Canberra. The ewes lambed from mid August to late September. The three management treatments were: (i) Continuous grazing (treatment CG). (ii) Ewes were confined to one-third of the whole area available in early pregnancy, so that feed was autumn-deferred for late pregnancy (treatment DP).(iii) Ewes were confined to a portion (one-third in 1956, one-half in 1957) of the area for the whole of pregnancy in order to ensure an adequate amount of feed for lactation (treatment DL). Two stocking rates and two breeds of ram were compared (Merino and Border Leicester). Treatment DL resulted in unsatisfactory liveweight gains during pregnancy, a far higher incidence of pregnancy toxaemia, reduced lamb birth weight, and increased neo-natal mortality. At the low stocking rate there were no significant differences between treatments CG and DP. At the high stocking rate, treatment DP reduced liveweight gain in early pregnancy and ensured an adequate liveweight gain in late pregnancy. The incidence of pregnancy toxaemia was lower at the high stocking rate in 1957 on treatment DP compared with CG. At the higher stocking rate, ditocous ewes on treatment DP gained more weight in late pregnancy than those on CG or DL.