Cattle with parasites graze less efficiently

Research has found that treating cattle for worms can potentially improve their productivity in the pasture

Cattle infected with parasites spend less time grazing and more time idling in the pasture, leading to lower weight gains compared to animals treated to eliminate parasites.

Though the study led by Andrew Forbes was published in Veterinary Parasitology in 2004, its findings emphasize the benefits of parasite treatment in cattle to potentially improve productivity.

Agriculture Canada research scientist Doug Colwell, who also studies cattle parasites, said he admired Forbes’ work on the study proving parasites do affect grazing behaviour.

“If they have nematodes in their GI (gastro-intestinal) tract when they are turned out on pasture, they will end up grazing differently and less efficiently,” said Colwell about the cattle study. “The worms, it does something to their behaviour.”

Forbes’ study, done with researchers C.A. Huckle and M.J. Gibb, involved 40 dairy cows and heifers that were allowed to naturally acquire gastro-intestinal nematodes when grazing. Twenty of the animals — 10 cows and 10 heifers — were then treated with pour-on eprinomectin to kill parasites. The others were not.

Researchers then observed grazing behaviour over 10 days, beginning four days after half the animals had been treated. Some were also periodically fitted with recorders to measure grazing and rumination behaviour.

“There were significant effects of treatment on grazing time, eating time, total bites, total grazing jaw movements, idling time and mean meal duration,” said the study.

“Treated cows and heifers grazed for 47 and 50 minutes longer per day, respectively, than controls. Mean meal duration was extended as a result of anthelmintic treatment by 11 and 38 minutes, in cows and heifers, respectively.”

Treated cattle also had increased milk solids, especially the heifers, and both the cows and the heifers had higher weight gain.

“This study has shown that adult dairy cattle, which typically have high levels of immunity to gastrointestinal nematodes and low parasite burdens, are still subject to nematode-induced inhibitory effects on appetite,” the paper said.

“Alleviation of these burdens, through eprinomectin treatment, resulted in increased appetite, manifested as increased grazing time, eating time and number of bites.”

In its information about internal cattle parasites, the Beef Cattle Research Council notes there have been no large studies on the economic impact of roundworms in recent years but studies from the northern United States indicate production gains when parasite treatment is provided.

Gains up to half a pound per day over 120 grazing days have been reported in treated versus untreated cattle.

“A good internal roundworm parasite control program should maximize production gains, minimize disease risk but avoid indiscriminate and unnecessary dewormer use,” the BCRC said in its post. “The aim is to use the correct product at the correct time on the animals that need it most.”

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