Winter crop choice and body condition loss change the eco-efficiency of sheep flocks
Lamb survival (ewe reproductive performance) and lamb growth are key levers to changing eco-efficiency, particularly in hill country systems. New research has highlighted reproduction losses when feeding some winter crop options such as fodder beet. Current research findings are used to understand the impact of changes in reproductive performance of sheep flocks caused by body condition change and winter forage crop choices on whole farm eco-efficiency. Eight farms were anonymously selected from an existing database, four with ‘low rainfall’ and four with ‘high rainfall’, averaging 590 and 1090 mm/annum respectively to represent the cool temperate climates of southern New Zealand. Ewe and lamb survival, and lamb liveweight gain to weaning were altered to reflect the impacts of either losing or retaining body condition in late gestation, either on a fodder beet or brassica diet in mid-late gestation. Ewes retaining body condition with fodder beet scenarios were fed a supplement added to ensure adequate protein nutrition using a combination of Lucerne hay, soy meal, and urea. General adjustments made to maintain pasture use similar to the original farms included adjusting lamb sales date, supplement making, stocking rate and autumn nitrogen use. Eco-efficiency was reduced using fodder beet as a winter forage as greenhouse gas emissions were increased per unit of product. The loss of condition score during mid to late pregnancy also led to a reduction in eco-efficiency, though this was more severe when feeding fodder beet. The impacts of fodder beet were mitigated if the diet was balanced for protein. Nitrogen and phosphorus loss from soil was low, and reduced under fodder beet feeding conditions, due to the smaller area of cropping than traditional brassicas.
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