Measuring differences in the efficiency of converting feed to liveweight gains of beef cattle depends on assessments of feed intake and animal growth over a specified period. Previous studies have shown that feed intake can be measured with sufficient precision after 35 days, however, to assess growth rate with acceptable precision, a feeding period of 70 days is required when the cattle are weighed fortnightly. In order to test if more frequent weighing could improve the precision of estimates of liveweight, or reduce the duration of tests, animals were tested in units where an automatic weighing system recorded the liveweight of an animal every time it entered a feeder. Eight groups of beef bulls (171 animals in total) were tested. A random coefficient regression model including a cubic spline for time was used to estimate average daily gain. Evaluation of the residual variance, slope (average daily gain), and its standard error from the models showed that through the use of automated liveweight measurement, the duration of tests could be decreased to 56 days without reducing the precision of estimates of liveweight change. Depending on the precision required, further decreases in testing time could be accommodated.
In this study we test the hypothesis that selecting sheep for a low behavioural reactivity to stressful situations will improve their metabolic efficiency, and thereby feed efficiency, during a controlled trial in an animal house. Twenty-four Merino wethers were used, 12 each from lines selected for high (HBR) and low (LBR) behavioural reactivity to stressful stimuli (human presence and social isolation). The sheep were habituated to the experimental procedures for 10 days, followed by 45 days during which voluntary feed intake was measured so that total daily energy intake was quantified. The sheep were weighed twice weekly before daily feeding. Feed efficiency was determined by measuring net feed intake, average daily weight gain and body condition score. Our hypothesis was not supported by the results of this study. There was no difference between LBR and HBR sheep in average daily weight gain or body condition score. The net feed intake of HBR sheep was lower than that of LBR sheep (P = 0.02), indicating that under the conditions of our experiment, HBR sheep were actually more feed efficient than LBR sheep. This study was carried out on sheep with steady intakes and in familiar surroundings. It is possible that LBR sheep may be more efficient than HBR sheep in more stressful situations.
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