Effect of change in body weight and condition during the dry season on capacity for work of draft oxen.

Work oxen supplemented at different levels during a feeding period of 3 months, were divided into 3 groups of average weight change -25, +35 and +70 kg and worked under loadings of either 7.5 or 12.5 kgf/100 kg of liveweight for 2 weeks, in order to assess the impact of dry season supplementation on capacity for work. At approximately equal levels of stress in work, manifest in maximum heart rate one minute after ceasing work (MHR), oxen with higher dry-season weight gain produced higher levels of work output, in proportion to their increased body weight. Rate of work and mean daily work output increased from the first to the second week of work, in spite of average daily weight losses of 2.63 kg throughout the period. Decline in rate of working through each day was continuous and essentially linear with relation to distance worked. The time taken to cover 1 km increased at an average of 0.16 and 0.68 min/km for light and heavy loadings respectively. Although MHR appeared to provide a retrospective measure of the level of stress attained in work, it was of limited use as a predictor of reasonable work demand. Maximum heart rate was related to work output (MJ) and animal liveweight (kg), as follows: MHR = 17.7 (+/- 3.94) WO - 0.15 (+/- 0.080) LWT + 118.5 (r2 = 0.70 P < 0.01).