Effects of field infestations of gastrointestinal helminths and of the cattle tick (Boophilus microplus) on growth of three breeds of cattle

Abstract

Approximately equal numbers of Shorthorn x Hereford (British), Africander x British, and Brahman x British yearlings (all F3-F4 generations), totalling 117, were run together on one pasture. One-third of each breed type was dipped every 3 weeks to control ticks, one-third was given injectable tetramizole at the same intervals to control gastrointestinal helminths, and one-third was untreated. The estimated increases in gains in body weight in 27 weeks due to dipping were 10 kg (10%) in Africander cross and 3 kg (3%) in Brahman cross animals (neither significant), but 27 kg (46%) in Shorthorn–Herefords (P 0.001). Anthelmintic treatment increased gains by 22 kg (22%) in the Africander cross (P < 0.001), and 1 kg (1%) in the Brahman cross group (not significant), and 18 kg (30%) in the Shorthorn–Herefords (P < 0.01). The differential breed responses to the presence of ticks were accounted for by differences in the numbers of female ticks maturing. The Africander and Brahman cross animals carried a mean of 20–30 ticks per side ompared with75–100 on Shorthorn–Herefords, and had higher repeatability of counts on individual animals. The regression of weight gain on tick count between animals within infested groups was similar to that between infested and dipped groups. There was no breed difference in counts of helminth eggs in faeces. There were significant differences between animals but they were not correlated with weight gain. Tick burdens were moderately high. Helminth egg counts were low. In these circumstances and under the pasture conditions represented, tick resistance accounted for 40% of the superiority in growth of the Brahman cross or Africander cross over Shorthorn–Herefords, and tolerance of helminths accounted for none of the difference between Africander cross and Shorthorn–Herefords, for 25–40% of the difference between Brahman cross and Shorthorn–Herefords, and for more than the observed difference between Brahman and Africander crosses. The effects of both parasites on growth, and the importance of differential responses of breeds, are conditioned by environmental conditions, notably nutrition.