Comparative cost-effectiveness of ivermectin versus topical organophosphate in feedlot yearlings

A replicated-pen field trial was performed under commercial feedlot conditi ons in western Canada to determine the cost-effectiveness of administering ivermectin to yearling beef cattle upon entry to the feedlot after the graz ing season, and to establish the level of trichostrongylid gastrointestinal parasite infection in this population, as estimated by fecal egg counts. S ix thousand eight hundred and eighty-three, mixed breed, yearling steers we re randomly allocated upon arrival at the feedlot to one of 2 experimental groups as follows: Ivermectin, which received topical ivermectin (0.5%) at the rate of 1.0 mL/10 kg body weight; or Fenthion, which received topical f enthion (20%) at the rate of 12 mL/295 kg body weight. There were 15 pens i n each experimental group. Final weight, weight gain, average daily gain, a nd dry matter intake to gain ratio were significantly (P < 0.05) improved i n the Ivermectin group as compared with the Fenthion group. There were no s ignificant (P greater than or equal to 0.05) differences in initial weight, days on feed, or daily dry matter intake between the experimental groups. The geometric mean fecal egg counts at the time of allocation were 14.7 egg s/5 g and 16.6 eggs/5 g for the Ivermectin and Fenthion groups, respectivel y (P greater than or equal to 0.05). There were no significant (P greater t han or equal to 0.05) differences in morbidity or mortality between the exp erimental groups. In the economic analysis, the significant improvements in feedlot performance in the Ivermectin group resulted in a net economic adv antage of $4.20 CDN per animal.