The margin of error for stocker cattle often is narrow — $50 per head can be the difference between profit and loss. It’s important to get the most out of that high-value calf with the lowest input, which means getting the most out of the pasture grass.

Once on pasture, those calves will encounter internal parasites, with potential contamination increasing as grazing season progresses. The result can be costly sub-clinical parasitism.

Internal parasites reduce feed intake, which decreases weight gain and marketing efficiency. But internal parasites also reduce the animal’s ability to fight viral disease by impairing the calf’s immune function, as well as reduced vaccination response.

Too often, convenience drives deworming programs. The process should start by consulting with your veterinarian to develop a strategic deworming program that will provide sustainable coverage for the herd and achieve your operational goals.

Because each anthelmintic class works differently and resistance to each class exists normally as small subsets within the parasite population, it’s important to monitor the program’s effectiveness. The reality is if you’re controlling internal parasites to some degree, the underlying negative results or costs may not be evident.

To look deeper into this, we set up a real-world trial to evaluate the performance, weight gain and cost of two deworming protocols for season-long control in calves on pasture.

The trial setup

The trial took place in Mississippi on a pasture fenced into two matching 400-acre segments. Two groups of English-Continental crossbred steers weighing 500 to 550 pounds were purchased and preconditioned upon arrival for 60 days, using standard processing protocols—– including deworming and vaccination — to ensure a uniform health status. All steers received fly treatment and implants.

For the trial, the North pasture contained 235 steers, weighing 626 pounds, for a stocking rate of 1.7 acres per head. The South pasture had 242 steers, weighing 624 pounds, stocked at 1.65 acres per head, representing no statistical difference between the groups.

At the start of the trial (day 0), the cattle received the following deworming treatments per label directions:

  • North pasture — An injectable, long-acting eprinomectin.
  • South pasture — A concurrent treatment of Safe-Guard® (fenbendazole) drench and generic ivermectin pour-on. This group also received Safe-Guard Dewormer Range Cubes on days 28 and 56.

Fecal samples were collected at the start of the trial and fecal egg counts were conducted. The eggs from the samples were sent to Colorado State University for polymerase chain reaction (PCR) testing to ensure that both groups were being challenged by the same genera of parasites. After that, 20 samples were taken from each group on days 14, 22, 28 and 42, and then every two weeks until the trial ended. For each testing period, samples from the five highest egg shedders from each group were sent on for PCR testing. 

The results

While on trial, the cattle were rotated within their designated pasture for a total of 120 to 140 days of grazing. Cattle in the South pasture, which received the concurrent treatment, gained significantly more weight in fewer days (see Figure 1).

Gaining 0.27 more pounds per day than their counterparts in the North pasture, the South pasture steers were 23 pounds heavier on average. Using an Oklahoma City-based average price of $2.30 per pound for 7- to 8-weight steers (quoted September 2014), those 23 pounds generated an extra $52.90 per head. Calculated across the 242 steers in the South pasture, that’s an additional $12,801.80 in income.

The combined cost of the fenbendazole and ivermectin concurrent treatment at turnout, followed by the two timed treatments of Safe-Guard range cubes, was 20 percent less than the cost for the single injection of long-acting eprinomectin (see Figure 2).

“The bottom line is we got 23 pounds more per head and it cost us 20 percent less,” said Mark Hazard, who hosted the trial at his Mississippi ranch where he custom-grazes cattle. “The cattle were the same, the grass was the same, and it didn’t take long for me to look at the cattle and tell which ones were doing better.”

Managing the parasite burden

It’s worth noting that neither group had an excessive parasite burden when the trial started. Tests showed that there was a continual presence of Cooperia and Haemonchus. Ostertagia declined at weeks 10 to 12 (mid-July to mid-August), which is typical during hot, dry periods.

The concurrent treatment group continually maintained lower fecal egg counts than the long-acting eprinomectin group throughout the trial (see Figure 3). The egg counts were statistically lower in the concurrent treatment group on weeks 2, 6, 10, 12 and 14. This is significant because the literature suggests that at nine to 10 eggs per gram is where a decline in feed intake and feed efficiency has been observed, which held true in this trial.1

The concurrent treatment group maintained lower fecal egg counts throughout the trial than did the North pasture steers. But most significantly, by the second week of the trial, the concurrent treatment group dropped fecal egg counts by 99.9 percent compared to just 65.5 percent for the long-acting eprinomectin group.

That’s important for a couple of reasons. First, the early drop in egg count by the fenbendazole and ivermectin concurrent treatment group lets the calf get the most out of the grass when the grass is at its best. Eliminating the internal parasite burden at turnout — then keeping the parasite burden at a low threshold throughout the grazing period with strategically timed pasture treatments of Safe-Guard range cubes — allowed the cattle to take full advantage of the available forage without the added stress or labor costs of gathering the cattle for re-treatment. 

Is your dewormer working?

There are a few additional take-home points from this trial. Whatever dewormer program you’re using, you need to ensure that it’s still working. Start by consulting with your veterinarian and/or a parasitologist to assist with diagnosis, treatment and control strategies. Run a fecal egg-count reduction test at least once a year, as well as PCR tests, to know which parasites you’re dealing with and how things are progressing. This involves collecting 20 fecal samples on the day cattle are dewormed and again 14 days later. You can find more sampling information at

Because of parasite resistance, the most effective strategy to control internal parasites, as well as ensure anthelmintics remain effective, is to concurrently use two or more classes of anthelmintics as compared to repeated use of a single class of anthelmintic or a rotational class of anthelmintic use.2

The comparison trial allowed Hazard to see the full potential of his pastures. “We were generally happy with both sets of cattle,” Hazard says. “But when you compared the results of the fenbendazole and ivermectin concurrent program, the cattle gained 23 pounds more per head and it cost us 20 percent less. We got more out of our grass and ended up several thousand dollars better off. That tells us what we need to do going forward.”

 1Smith RA, Rogers KC, Huse S, Wray MI, Brandt Jr. RT, Hutcheson JP, Nichols WT, Taylor RF, Rains JR, McCauley CT. Pasture Deworming and (or) Subsequent Feedlot Deworming with Fenbendazole. I. Effects on Grazing Performance, Feedlot Performance and Carcass Traits of Yearling Steers. The Bovine Practitioner. 2000;34(2).

2Field Efficacy of Multiple Anthelmintics in US Cattle using the Fecal Egg Count Reduction Test. Antiparasitic Drug Use and Resistance in Ruminants and Equines Public Meeting. March 5-6, 2012.