The brown stomach worm, Ostertagia ostertagi, is the most common and economically important parasite in cattle, with an estimated cost to the U.S. cattle industry of $2 billion per year due to lost productivity and increased operating expenses, according to Boehringer Ingelheim.

“On beef and dairy operations, we’re not seeing the traditional signs of worms, such as skinny animals with rough hair coats, anymore,” said Dr. Stephen Foulke with Boehringer Ingelheim. “Instead, internal parasite infections manifest as poor productivity, including reduced feed intakes, slower growth rates, delayed breeding, decreased milk production and depressed immune responses.”

Studies show that a brown stomach worm infection can reduce cattle weight gain by up to 20 lb., whereas milk production can see a decrease between 2 lb. and 5 lb. per day, Boehringer Ingelheim said, pointing to research published in 2006.

Unlike other stomach worms, the brown stomach worm has the unique ability to penetrate the lining of the abomasum and become dormant, so it can survive during weather that’s too cold or too hot. When conditions improve, the larvae can emerge all at once, causing severe inflammation and irritation, reduced feed intake and sometimes even death, Foulke said.

Foulke explained the basic life cycle:

1. Adult parasites lay eggs in the gastrointestinal tract of cattle.

2. Eggs are expelled from the cattle through feces.

3. Eggs hatch and develop into infected larvae.

4. The infected larvae crawl onto the grass on which cattle graze.

5. Larvae are ingested by cattle.

Stocking density and weather conditions can influence the likelihood of this cycle continuing and, consequently, the number of parasites present at any given time.

“Parasites place themselves in the best position to be ingested by cattle,” Foulke explained. “They try to stay at the top of the grass blades during the day and migrate back down to ground level overnight.”

Studies have found that the climate at the base of the grass is very favorable for larval survival and can harbor large numbers of parasite larvae, Boehringer Ingelheim said. Some larvae migrated as far as 15 cm down into the soil and were able to return to the surface to be ingested.

Rainfall and other adverse weather conditions allow larvae to be more easily transported away from the fecal matter. In fact, a minimal amount of water can transport larvae up to 35 in. away from their original location.

To best protect a herd from parasites, Foulke encouraged producers to look for a weatherproof dewormer. A local veterinarian can help determine the parasite load in a herd and on a pasture throughout the year as well as adapt control methods to manage parasites in all weather conditions.

“Since the parasite life cycle typically revolves around pasture contamination, confined dairy operations may not view the brown stomach worm as a threat, but we forget that many of these confined dairies will still put dry cows or calves and heifers on pasture,” Foulke noted. “If animals see grass at any point in their life, they’ve likely been exposed to parasites like the brown stomach worm.”

Dairy producers are encouraged to pay special attention to parasite control in replacement heifers, as they have significant nutrient demands on their bodies during the growing stages, Boehringer Ingelheim said. Adding parasites to that equation can slow time to mature weight and conception, which gets them into the milking string late and, ultimately, decreases lifetime milk production.

Managing brown stomach worms

“Producers often ask about the best deworming protocol, but unfortunately, that answer is different for every farm,” Foulke said. “The way you’re going to deworm a dairy herd in the Northeast is going to be very different than deworming a stocker operation in Florida.”

To minimize the impact these parasites can leave on herd performance and profitability, Foulke advised beef and dairy producers to work with their veterinarian to perform routine fecal tests on their cattle and implement management protocols accordingly.