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

Abstract

The effect of the tick Boophilus microplus on the liveweight of Bos indicus x B. tauvus 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 of the three periods were 0.72,0.47 and 1.52 gper tick respectively. The 1980 estimates were significantly lower (P < 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. Mean tick survival rates varied from 9% in summer 1980 to 25% in autumn and 2% in summer 1981. They were reduced at higher densities but were unaffected by the nutritional supplement. 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. With a mean loss of 0.6 g per tick and 1983 dipping costs of $A1.35, the economic threshold is 158 ticks engorging per day per animal, assuming a kill of 97 %.