Deworming those stale, hollowed-out fuzzballs coming off the truck is an easy decision. But what about adding the cost of parasite control to a set of calves that appears to be in the pink, especially if those calves are coming from a part of the world that isn't known for dense populations of internal parasites? Or, what if you're turning those same healthy-looking calves out on pastures during a time of year when parasite challenges should be at their lowest?

If you're Jason Sawyer, a Texas A&M University (TAMU) stocker specialist, you're going to assume every stocker calf arriving at your place is carrying at least some parasite burden. You would also know that it's a rare instance when taking the bugs by the horns fails to return more than the investment.

“We do some management practices for insurance, but parasite control is the best kind of insurance. It protects your investment and generally pays you back more than it costs,” Sawyer says.

In fact, after reviewing a bevy of research trials regarding the impact of parasite control in the stocker pasture, Sawyer says, “I'm comfortable suggesting 0.2 lb. of improved gain can be expected, even at low levels of infection.” The trials dealt primarily with calves of the five-weight variety, running in stocker pastures 120-160 days.

Of course, that's not saying deworming every set of stocker calves will yield this specific performance boost. As Sawyer says, making the decision is situational.

“The 0.2-lb. additional rate of gain should be adjusted based on the likelihood of infection,” he explains.

For example, if calves are coming from areas known to produce large parasite burdens, budget 0.2 lb. in making the decision. As the likelihood of infection decreases, reduce the potential return accordingly.

How worms work

Using Ostertagia (the brown stomach worm often cited as the most economically devastating of internal parasites) as an example, the larvae embed themselves in the abomasa of cattle and irritate the gastric glands. This increases production of appetite-suppressing enzymes. The internal disruption also interferes with protein metabolism, so less protein is available for production of antibodies.

Steve Wikse, DVM, associate professor of large animal medicine in TAMU's College of Veterinary Medicine, explains that Ostertagia can survive as arrested larvae in the abomasa of cattle during the long, hot summers of the South and the long, cold winters of the North. Larvae can survive in fecal matter and are released during autumn rains in the South and spring rains in the North.

On both counts, cattle are exposed to the greatest numbers of Ostertagia during the rapid growth of cool-season forages. This means cattle in the South typically receive the most exposure in the spring (March through mid-May); with cattle in the North, it's in September and October.

What's more, the only accurate, objective way to gauge parasitic burden is with a blood test. Outside of research trials, however, the cost and labor associated with such tests makes them impractical as a normal business practice.

“Fecal egg counts are how we would historically have measured the level of parasitic infection,” Sawyer says. “But, there's currently mixed opinion on the value of them.”

For one thing, if you find eggs, there is debate about what various quantities mean in any given situation. Plus, there's no way to measure the maturity of discovered eggs.

“As a practical recommendation, I'd first base the assessment of parasitic infection on the climate where cattle originated and where they will be grazed. In areas that are conducive to parasites (mild winters and warm, wet springs), you assume you have a burden,” Sawyer explains.

The best investment

There's little downside to internal- parasite control, as even minimal response can return far more than the cost. Using quick cowboy math, just 0.1 lb. of additional gain would amount to 12 additional lbs. over the course of 120 days (Table 1). The net between that and the $5-$8/head Sawyer calculates it costs to deworm stocker calves, depending on the product, represents a blue-chip percentage return on investment.

In the studies he re-viewed, Sawyer points out, “Cattle stay pretty clean (free of infection) for the first 28 days after treatment. By Day 56, the parasite burden will increase due to re-infection from the pasture. What that tells you is that you're getting a lot of the response early on.”

According to Sawyer, that means response to control should last for a longer period of time when it's applied in seasons when parasite burdens should be at their lowest.

The reality of re-infection, combined with the sensitive response to control, also means re-treatment can pay during longer grazing seasons in certain situations. For instance, Sawyer says, “There are pastures in this part of the country with such consistent parasite burdens that you could probably see performance response if you re-treated cattle every 60 days.”

Even with positive response, though, Sawyer points out that the cost of gathering and treating calves multiple times ultimately overtakes the returns.

Moreover, Sawyer emphasizes, “If nothing else, I would prefer that newly arrived cattle not contaminate or further contaminate my pastures.” As mentioned earlier, parasite burdens are difficult to assess, even on cattle with a known history.

Consequently, Sawyer believes parasite control is a standard part of processing protocol for most veteran stocker operators.

Those who sacrifice the practice, periodically or completely, do so for a number of reasons. In some cases, Sawyer says it's because they're running cattle for other owners on a lease basis, so the incentive to incur added cost isn't there. More often, though, he finds the folks not using parasite control are folks new to the notion of growing calves after weaning.

“More than ever, cow-calf producers understand calves have a performance life after they leave the ranch. But, some are still not aware of how specific management practices impact profitability later on,” Sawyer says. That can be true whether producers are selling their calves or choosing to retain them through a growing program for the first time.

Some common sense

When running stocker cattle for the first time, or running calves for the first time on unfamiliar ground, Sawyer encourages operators to consult with their veterinarian and/or a veterinarian local to their cattle's grazing area in order to design an effective parasite control program. They're the ones who know which parasites represent the major challenge in a given season and set of circumstances.

Once the challenge is defined, Sawyer says it's tough to find a parasite control product that doesn't work.

“If you're buying products from a reputable manufacturer, using them for what they're labeled for and applying them according to the label, the product should work effectively for you,” he adds.

As far as Sawyer is concerned, parasite control boils down to managing risk by avoiding catastrophic loss, and by using a tool that generates a consistent return on investment‥

“We have multiple risks in our business,” Sawyer says. “Parasite control and other management practices are tools we can use to mitigate production risk. Parasite control is part of comprehensive risk management.”

Table 1. Value of response to parasite control

Response to parasite control lbs. of gain/day) No. of Grazing Days Total Added Gain (lbs.) *Value of Response ($)
0.10 120 12.0 $12.00
0.10 150 15.0 $15.00
0.15 120 18.0 $18.00
0.15 150 22.5 $22.50
0.20 120 24.0 $24.00
0.20 150 30.0 $30.00