The effect of cattle tick (Boophilus microplus) on the growth of Bos indicus x B. taurus steers

The effect of the tick Boophilus microplus on the liveweight of Bos indicus x B. taurus steers was investigated using three levels of infestation during summer 1980, autumn-winter 1980 and summer 1981. Mean losses in liveweight per engorged female tick during each to the three periods were 0.72, 0.47 and 1.52 g per tick, respectively. The 1980 estimates were significant lower (P less than 0.05) than that in summer 1981, and the losses were independent of tick density. The loss per tick was unaffected by a supplement of molasses and urea in the autumn-winter period. Compensatory growth of those steers whose earlier growth was retarded by poor nutrition or ticks was investigated by keeping all the steers tick-free during spring. The previous medium and high tick groups gained 5-6 kg per animal more than the low group. Non-supplemented animals recovered all of their 14 kg disadvantage compared with the supplemented group. The large variation in losses in liveweight per tick on these animals on the same pastures at different times suggests that differences in published estimates are frequently due to animal variation rather than to nutrition, cattle breed or environment. Economic thresholds were calculated for a range of effects of ticks and of chemical control costs