A recent study at Louisiana State University (LSU) sought to determine whether worms or flukes were the more important internal parasite in cattle, and what happens if cattle have both? 

Conducted over a four-year period at LSU’s Alexandria experiment station, weaned heifers each year were divided into four groups of 24 head. One group was treated with injectable ivermectin – to kill worms but not flukes. Another was treated for liver flukes only, using Curatrem (containing clorsulon). The third group was treated for both worms and flukes with both products, and the fourth group served as untreated controls.

The heifers grazed ryegrass pasture in winter and were supplemented with corn-based concentrate to gain 1 lb./day in order to reach breeding weight. The pastures were known to have both worms and flukes.

Results showed gastrointestinal (GI) tract nematodes had the most profound impact on gain.

“Compared with the untreated control group – which actually did well, gaining 1 lb./day (53 lbs.) – the dewormed heifers averaged 23-25 lbs. more. They gained more than needed for breeding weight. That group could have been backed off a little on feed, which would have saved a lot of money,” Hawkins says.

The group that perennially did best received both worm and fluke control. They registered better weight gain, and increased conception rates, while the heifers treated for just flukes gained 23 lbs. more than the untreated controls, on average, Hawkins reports.

Moreover, the study found worms were more important than flukes for affecting weight gain, which is probably representative of most ranch situations, researchers say.

“But if a producer sees signs of heavy fluke infections, this could be different. I’ve seen several instances in which young cattle – replacements or stockers – died on pasture from liver failure,” Hawkins adds.

Heather Smith Thomas is a rancher and freelance writer based in Salmon, ID.