Differences in susceptibility to gastrointestinal nematode infection between Angus and Brangus cattle in south Louisiana

Breed susceptibility to nematode infection was evaluated in Angus (Bos taur us) and Brangus (B. indicus crossbreed) cattle. A cow-calf herd and a yearl ing replacement heifer herd were monitored during one grazing season. Calve s were born in March and were weaned in October. Individual rectal fecal sa mples were collected monthly from the two herds and processed for fecal egg counts (FEC) and coprocultures. Cow and calf FEC increased from April, rea ching maximum values during the summer. Angus cows and calves had significa ntly (p < 0.05) greater FEC than Brangus cows and calves, and Haemonchus an d Cooperia were the predominant genera. Replacement heifer FEC showed a sim ilar pattern with maximum levels during late summer/fall, and Haemonchus wa s the predominant genus, No significant differences were seen between breed s, however, infection levels were consistently lower in Brangus heifers. Os tertagia was present in cows and heifers only in fall/winter, which is cons istent with summer inhibition. The data suggested that cows were an importa nt source of pasture contamination for their susceptible calves and that th e Brangus breed was relatively more resistant to infection. The use of B. i ndicus crossbreeds may help in alleviating reliance on chemical control by reducing the rate of pasture contamination and subsequent infection losses. (C) 2000 Elsevier Science B.V. All rights reserved.