Is the fasting period a mandatory procedure for estimating body weight gain in beef cattle?

Context To mitigate the influence of gastrointestinal tract and urinary system contents on the quantification of average daily gain (ADG), a fasting period prior to the weighing procedure has been recommended. Nonetheless, fasting prior to weighing may increase animal stress, thereby potentially compromising welfare. Aims We investigated whether there are differences in the estimates of ADG, as well as whether there is a decrease in the random variability of experiments with solids fasting in cattle prior to the weighing procedures. Methods A database was compiled from eight experiments conducted with growing and finishing animals, totalling 214 animals. Analyses of variances were performed within each experiment to evaluate the effects of the fasting period on residual variances. Subsequently, the data were analysed according to a meta-analytical approach to assess the relationships between ADG with and without fasting, and body weight (BW) variation caused by the fasting period as a function of animals’ BW. Key results Residual variances for ADG within experiments were not affected (P ≥ 0.29) by a fasting period prior to weighing. Moreover, estimates of ADG did not differ (P ≥ 0.05) when estimated with or without a fasting period. The relationship between absolute BW loss after fasting and animals’ BW was constant (P < 0.05). However, the relative values of weight loss (%BW) after fasting presented a decreasing exponential pattern as the animals’ BW increased (P < 0.05). Conclusions Fasting in cattle under experimental conditions prior to weighing does not influence ADG estimates, nor does it affect experimental random variability. Implications Fasting animals prior to weighing is an unnecessary practice, as it neither affects ADG estimates nor alters experimental precision. Moreover, omitting fasting promotes better animal welfare, as it avoids infringing animal rights.