Impacts of winter crop choice and ewe body condition score change on whole farm profitability and production

Abstract

Variations in body condition score (BCS) in ewes influences lamb survival, ewe survival and ewe lactation performance. Feeding a low protein diet such as fodder beet to ewes in mid-to-late pregnancy increases lamb losses and reduces lamb weaning weight even further. However, using high yielding forages such as fodder beet can reduce the area of winter crop required, introducing potential whole-farm benefits which may alter profitability. We analysed the effects of winter crop choice (brassica or fodder beet) and BCS (maintaining or reducing) on whole-farm production and profitability, using a targeted supplement to offset the impacts of fodder beet feeding. Eight farms were selected to represent low or high rainfall (590 and 1090 mm/annum respectively) regions of the South Island. Impacts of changing BCS on ewe and lamb survival at lambing, and lamb liveweight gain to weaning were calculated when fed either adequate (brassica) or low protein (fodder beet) diets in mid-to-late pregnancy. Production statistics and profitability were calculated using Farmax. Whole farm profitability was analysed using BCS change and winter forage crop as main treatments, blocked by low or high rainfall. Applying the effects of BCS and low protein diets on reproductive performance from prior published studies resulted in variation of 102 to 141 lambs weaned per 100 ewes mated, with the lowest value when the low protein, fodder beet only diet was used. Greatest number of lambs weaned was achieved when BCS was maintained through winter through provision of a balanced supplement, regardless of winter forage diet (P<0.05). Lamb sale dates were later when fodder beet was used, due to lower lamb weaning weights, resulting in marginally higher prices due to changes in pricing schedule. Farm profitability was increased by 25% when BCS was maintained though winter (P<0.05) irrespective of the diet used. Use of fodder beet must be accompanied by targeted supplementation to avoid ewe BCS loss increased lamb losses and the negative effects on wastage and animal welfare. Extra profitability could only be generated by opportunities to sell surplus feed during the summer. These responses were similar in both high and low rainfall environments. This study is unique in testing measured responses of BCS and targeted nutritional supplementation under specific physiological conditions on whole-farm profitability. Farmer decisions on feed utilisation and sale also have a significant influence on the potential to mitigate the effects of variations in winter forage choice.