Time to collapse was assessed by two independent observers on the first 112 animals to determine whether there might be any observer bias. It was found that the observations for time to collapse were significantly correlated between the observers, with r = 0.90 (95% CI 0.87–0.94) P < 0.001. Thereafter one operator performed all subsequent recordings of time to collapse. Furthermore, to test for sampling drift the results were analysed for sample day effects, and no significant associations were found (P < 0.564). There were no significant interactions between animal breed, age or gender on the time to collapse or other recorded parameters.