Effect of an Eprinomectin Treatment at Fall Housing on Milk Production of Dairy Cows in Québec

Abstract

Dairy cattle in Quebec are exposed to gastrointestinal nematodes throughout the grazing season, from May to October. The clinical and economic impact of these parasites, especially Ostertagia ostertagi, is well documented in replacement animals. In severe cases, clinical disease (diarrhea, weight loss and death) can be seen, but in most cases the infestations are subclinical and may lead to decreased productivity (reduced average daily gain). Many deworming products and protocols have been proposed to enhance dairy cattle productivity. The efficacy and economic justification of some of those are not always evident, especially for lactating animals. Animals over 2 years of age rarely show clinical signs of digestive parasitism, and clinical trials using a wide range of parasite control products have shown variable effects on lactation productivity. The discovery of the avermectin endectocide family was a major advance in clinical parasitology. Avermectins were shown to be highly effective and to improve dairy cattle productivity but they only were available for use in heifers and during the dry period, due to milk withdrawal times. The recent approval of eprinomectin with no witholding time for meat or milk has allowed the treatment of dairy cattle of all ages at any time of lactation.

The objective of this study was to determine the response in milk production of dairy cows treated with eprinomectin at fall housing.