Brief communication: Optimizing a fasting protocol to assess live weight of sheep

Abstract

Measurement of live weight is prone to variation from a number of sources. The largest of these is likely to be the weight of digesta in the rumen, which can contribute up to 17% of the measured live weight, and is influenced by a number of factors associated with both animal grazing behaviour and feed characteristics (Hughes 1976; Orr et al. 1997; Gregorini 2012). Accounting for the potential variation in liveweight estimates caused by gut fill may therefore provide greater accuracy of liveweight records. It may be expected that the variation in liveweight estimates caused by gut fill can be reduced through fasting, with periods of 24 h typically used. For commercial farmers who collect liveweight information either to assist with management decisions, determine the nutrient status (van Burgel et al. 2011) or pregnancy status (Judson & Nicol, 1993) of ewes, this length of time may be unacceptable. Given that live weight continues to decline even after 48 h fasting (Warriss et al. 1987), the error associated with gut fill is unlikely to be completely eliminated. Fasting for shorter periods may be able to reduce the variation in liveweight estimates caused by gut fill to assist obtaining liveweight measurements within a time frame that is acceptable for use in commercial situations. However, there is a paucity of published data surrounding the variation in liveweight estimates with time of fasting. The objective of this study was to quantify the variation in liveweight estimates at varying times of fasting and identify the minimum fasting time required in order to develop appropriate fasting and weighing protocols for commercial situations.