Summer production of sheep grazing irrigated and non-irrigated pasture

At Werribee in southern Victoria changes in liveweight, wool growth and carcase weights were measured over a 96 day period in summer during which two-year-old Corriedale and Merino ewes grazed various combinations of irrigated perennial and non-irrigated annual pasture. To provide the different combinations of grazing, groups of each breed grazed the two pasture types for different periods of time in 8 or 32 day grazing cycles. Groups with an eight day grazing cycle spent 1, 2, 3, 4, 5, 6, or 7 days (the 32 day grazing cycle groups 4, 8, 12, 16, 20, 24 or 28 days) on the irrigated pasture before completing the grazing cycle on the non-irrigated pasture. Two other groups grazed on either irrigated or non-irrigated pasture throughout the 96 days and a further group was slaughtered on day 1 of the experiment to measure the effect of treatments on carcases. The results were examined by regression analysis and showed that both breeds declined in liveweight, carcase weight, and wool growth on non-irrigated pasture. Production improved with time spent on irrigation. Corriedales (initial liveweight 47.0 kg) fattened when grazed on irrigated pasture for 50 per cent or more of the time but Peppin Merinos (initial liveweight 40.1 kg) could not be fattened beyond their initia carcase weights on any treatment. Wool production increased linearly with time spent on irrigation and was greater in Corriedales than in Merinos. The sheep grazing pastures in consecutive 8 day cycles did not differ significantly in production from sheep on similar treatments in the 32 day cycle.