It may be drier than a teetotaler's liquor chest in some part of the world, but drought conditions can actually increase the challenge of parasites, says Dave Sparks, DVM, Oklahoma Cooperative Extension Service food animal quality and health specialist. In a recent issue of Oklahoma State University's Cow Calf Corner, Sparks says normal late-summer forage height means parasites are often a minimal challenge this time of year. He explains about 80% of parasite larvae reside on the lower 2 in. on a forage plant; most can't crawl higher than 4-5in.
"If your animals are grazing 1- 2 1/2- in.-tall forage, they may be getting large numbers of infective larvae, even though it's dry. You can help to alleviate the problem by watching your animals graze," Sparks says. "Try to avoid this danger zone if possible and/or modify your de-worming program to fit the conditions."