Subclinical Effects and Control of Abomasal Worms in Dairy Cattle

Abstract

In the last decade considerable attention has been focussed on subclinical effects of internal parasites, particularly with respect to a possible reduction in milk yield in lactating cows. Subclinical effects have also been demonstrated in young animals and include depressed growth rate and interference with energy and nitrogen metabolism. These changes are largely related to infection with the abomasal worm Ostertagia ostertagi, which appears to be the most important pathogen in the U.S.A. and sometimes accounts for over 90% of the worm burden. In this presentation, the magnitude of the problem will be compared to young and mature dairy cattle and control strategies suggested.