The Unwelcome Guest
Permanent pasture parasites don’t have to kill profits.
By Nicole Lane Erceg
In today’s cattle market, every dollar counts. So anything eating away a rancher’s bottom line is unwelcome and uninvited. Making their home in pastures across the U.S. is a prevalent population of parasites on a mission to cause problems. From a calf’s first bite of grass to its last, the animal will have to deal with parasites, however, ranchers don’t always have to tolerate them worming into profit margins.
The No. 1 issue heavy parasite loads create is a reduction in feed intake. In a world where pounds equal profit, it’s impossible to gain when a calf doesn’t eat. When cattle can’t take in calories, there is no hope for cost-effective growth.
According to Harold Newcomb, D.V.M., technical services manager for Merck Animal Health, the problems don’t stop at the feed bunk. He says parasites also impair a calf’s immune system, leaving the animal at risk to viral disease and unable to effectively launch an immune response when given a vaccine.
Newcomb says that creating a successful deworming program can help ranchers see an economic benefit and a difference of a 20-pound gain in average weaning weights if done correctly. When developing an effective deworming program, Newcomb encourages producers to look beyond the general burdens of parasites and consider the growing drug-resistance of parasite treatment options, too.
“Parasites have been here since the earth was cooling and they’ll figure out a way around chemical treatments,” says Newcomb. “So part of problem-solving is going to be concurrent class deworming, pasture management and it could include forage selection.”
Resistance is real
The parasite population is growing stronger and smarter, evolving to resist drugs that previously worked well as treatment options.
“Macrocyclic lactone- or avermectin-resistance is an emerging problem in the U.S. and actually it’s pretty widespread,” says Newcomb. “Merck Animal Health maintains a database where it looks at the 3 major classes of dewormers. In the avermectins, which would be macrocyclic lactone, you can actually see the decline in efficacy over the years.”
As parasite resistance becomes a growing problem for the U.S. cow herd, Newcomb says it’s important to use treatment options that don’t contribute to the problem, while at the same time effectively managing the parasite burden in the cattle.
“Concurrent class use is probably the best way that we have to attack a resistance problem,” says Newcomb. “We only have 3 classes of dewormers in the U.S. and we need to protect all 3 classes, keeping each one working. Resistance is something that any class of dewormer can develop.”
The 3 classes of dewormers available in the U.S. are macrocyclic lactones, which include all the avermectin products, ivermectin, eprinomectin, moxidectin and doramectin; benzimidazoles that include white dewormers such as fenbendazole; and imidazothiazoles such as levamisole.
In all parasite populations, there is a percentage of worms that are resistant to 1, 2 or all 3 of these dewormer classes. Newcomb says the key to proper treatment without contributing to the resistance problem is concurrent class deworming, a process where 2 or more classes of dewormer are used simultaneously.
Make a plan — strategic deworming
When it comes to choosing a product and process, Newcomb says it pays to have a plan.
The actual problem lives on the pasture where 90 to 95 percent of parasites live. Only 5 to 10 percent of the parasite population makes their home in the cow. Newcomb recommends treating the animal when it will have the most negative impact on the lifecycle of the worm both inside the animal and on the grass.
“We want to kill off the worms in the cow at a time when it will be most harmful to the parasite on the pasture as well,” says Newcomb.
Through consistently keeping 4 to 6 inches of stubble in the pasture, producers can also help control parasites. Parasite larvae can only climb about 3 to 4 inches, so longer pasture grasses help avoid the spread of parasites from grass to a calf.
He says the most optimal time to deworm is about 6 to 8 weeks after cattle are put out on grass in the spring. This ensures that the animal has had ample time to build up a parasite load. By treating at this time, Newcomb says a producer reduces the amount of egg shedding that occurs, stopping the parasite lifestyle. For producers in the South, he recommends deworming again 6 to 8 weeks later using a concurrent feed-through form.
When it comes to dosing, Newcomb advises dosing the animals based on their weight — not the average weight of the herd, but individual weight.
“If you are dosing based on average weight you are under-dosing half the animals,” says Newcomb.
When making deworming program decisions, Newcomb recommends getting help from the experts.
“Work with a veterinarian or a parasitologist to develop a deworming program for your operation that meets your goals because every operation is different,” he says. “A blanket one-size-fits-all deworming program may not work for everybody. Tailor a deworming program to meet your specific needs.”
Is this working?
No matter what dewormer or program a rancher uses, Newcomb says it’s vital to double check that it’s doing its job. Performing a fecal egg count reduction test (FECRT) is an easy way to determine if a deworming program is effective.
An FECRT is when 20 animals from the same cohort group are sampled at the time of deworming and then another 20 are sampled again 14 days later.
These animals must be under 18 to 24 months of age because those cattle provide what Newcomb calls the “truest picture of parasitism” in the herd.
The FECRT results will determine whether the deworming program and products used were successful. Newcomb says a 90 percent reduction in the fecal egg count is considered a successful deworming and if a producer doesn’t meet that exact number or higher, they should seriously investigate further and adjust their program to fix the issue.
“This is a pass/fail kind of thing,” says Newcomb. “It’s not like horseshoes and hand grenades where close will get you by. If you are 90 percent or better, you’re okay. If you’re at 89 percent or below, it’s a fail.”
He says producers who find themselves in the failing group need to consider whether the deworming and dosage was done correctly. If so, he says to work closely with a parasitologist and veterinarian to determine the problem because a producer could be dealing with drug resistance. To set up an FECRT, producers can contact a parasitologist, local veterinarian or their Merck Animal Health representative.
Parasites may be an unwelcome permanent pasture resident, but with proper planning and management, their negative impacts on profits can easily be avoided.
“Unwelcome Guest” is excerpted from the March 2017 issue of The Cattleman magazine.