Could Parasites Be Cutting into Cattle Returns?

A good forage year does not always translate into the gains a producer expects. Warm, moist conditions that help grass grow can also help parasite larvae survive on pasture. That makes internal parasites worth a closer look this fall, especially when cattle appear healthy but their performance falls short. Recent Western Canadian feedlot research suggests even modest parasite loads may have an effect by the time cattle reach slaughter.

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Results from the Feedlot Study

Researchers measured parasite egg counts in 234 steers when they arrived at a Western Canadian feedlot. Nearly all of them, 225, had evidence of internal parasites. The average count was nine worm eggs per gram of manure. The cattle were then monitored through backgrounding, finishing and slaughter.

The relationship between those initial counts and the final carcasses caught the researchers’ attention. For every additional 10 eggs per gram measured on arrival, average daily gain was lower by enough to reduce slaughter weight by about 14 pounds. The odds of grading AAA rather than AA were also 29.5 per cent lower. These figures describe associations observed in this group of feedlot steers; they are not a guaranteed loss for every animal with the same egg count.

The study also compared steers treated with injectable ivermectin, steers given ivermectin plus oral fenbendazole and a control group treated only for external parasites. The two internal parasite treatments reduced fecal egg counts, but neither produced a measurable difference in overall weight, daily gain, feed intake or feed efficiency between groups. There were differences in carcass marbling grades. That mixed result is a useful reminder that finding parasites does not, by itself, tell a producer which treatment will pay on their operation.

Check the Herd Before Choosing a Treatment

The feedlot study did not test reproductive performance in a cow herd. Still, the Beef Cattle Research Council notes that internal roundworms can affect gains, milk production and reproductive efficiency, and that parasite pressure varies with weather, pasture use and the animals being grazed. It also warns that repeated dewormer use can contribute to resistance.

That makes testing more useful than assuming every herd needs the same fall treatment. A veterinarian can advise when to collect manure samples, interpret fecal egg counts alongside cattle condition and grazing history, and decide whether treatment is warranted. If a product is used, follow-up testing can help show whether it worked.

After a summer of better forage growth, producers have put considerable work into feed for the months ahead. The research gives them one more reason to check whether the cattle are getting the full benefit of it.