Observations on nematode parasitism in cow-calf production systems in southcentral/southwestern USA

Abstract

Observations on fecal egg count (FEC) and nematode identification data were compiled to help determine the extent of nematode parasitism in cows and their nursing calves. Overall mean FEC values for cows in Utah, Louisiana, Navada, Texas, and California were 7 eggs per gram (EPG), 6 EPG, 9 EPG, 10 EPG, and 15 EPG, respectively. Overall mean FEC values for nursing calves from the same states were 7 EPG, 228 EPG, 3 EPG, 60 EPG, and 398 EPG, respectively. The overall mean FEC value for Arizona cows was 33 EPG. Relatively complete seasonal FEC data were available from California and Louisiana where fall-born calves acquired high nematode burdens (i.e. 400–500 EPG) as early as 3 months of age, and spring-born calf FEC started low (10–30 EPG) and reached high levels (200–400 EPG) at about 5 months of age. In California, tracer calf data indicated that Ostertagia and Cooperia were the predominant nematodes acquired from pasture. In Louisiana, tracer calf, tracer cow, slaughtered calf (at weaning) and coproculture data indicated that Ostertagia (fall/winter) and Haemonchus (summer/fall) were the predominant nematode genera acquired by cows and that Ostertagia (winter/spring), Haemonchus (summer) and Cooperia (all seasons) were the predominant nematode genera acquired by calves. The acquisition of nematodes in tracer cows was much lower than in calves; however, the percentage of inhibited Ostertagia (ranging from 0% in summer to more than 80% in spring) was similar. A survey of abomasal nematodes in culled dairy and beef cows in Louisiana indicated that cows can harbor large (mean of 24 543 for beef and 16 383 for dairy) burdens. Burdens ranged from a few (100–200) worms to a high of 192 668 (almost all inhibited Ostertagia) in one animal.