A Strategic Approach to Reducing Internal Parasites
By Ellen H. Brisendine
Spring. New grass, new leaves, new calves and an emerging crop of gastrointestinal nematodes to infest your cattle. Brings a grimace to the face, doesn’t it?
Dr. Harold Newcomb, cattle technical services veterinarian with Merck Animal Health, says spring is the season to act strategically to “lower the worm burden in the pasture.”
The way to lower the worm burden is to treat the cattle strategically when you can do the most damage to the parasite population, in the animals and on the pasture where 90-95% parasite population lives in the form of eggs and larvae. Discing or turning the soil and planting a prepared seed is another way of lowering the parasite burden on the pasture. Growing tall forage such as Haygrazer, which grows taller than the worm larvae can crawl, is another option to help keep parasite burdens low in animals after they have been dewormed but this may not work for every cattleman.
This leaves ranchers with strategic treatment options to reduce internal parasites.
“The way we do that is by treating the cattle about 6 weeks after grass greens up and the cattle start grazing on the spring pastures,” Newcomb explains.
“In that 6-week period, the grazing cow is picking up the parasites. In an adult cow, it takes around 6 to 7 weeks for that worm to develop into an adult worm and start producing eggs. So, just about the time those worms have matured in that animal and start producing eggs, we’re going to deworm the animal, killing the worms and stopping egg shedding back onto the pasture.” We will repeat this process in another 6-7 weeks in the deep South, allowing the animals to go out and harvest another bunch of parasites and deworming again about the time the new bunch of parasites would start producing eggs. At this time, we should be approaching the hottest and driest part of the summer. The hot and dry summer heat will help keep the parasite burden low by drying out and killing the parasite larvae and inhibiting egg development on the pasture.
Newcomb says the best idea is to use a product that kills both the mature and immature forms of gastrointestinal parasites. “At just about the time they’re starting to reproduce, we deworm the cattle and kill the parasites.”
Repeat the deworming in another 6 weeks to kill the next batch of parasites. At that point in most of Texas and the Southwest, under normal weather conditions, “you can depend on the hot, dry summers to help control the parasites on the pasture.”
Newcomb understands that gathering all the cattle for a second deworming can be challenging.
He recommends using a feed-through formulation for the second treatment.
The mineral products that contain deworming medications, such as Safeguard, are a very nice way to get it done.” Merck Animal Health maintains a database on the field efficacy of different anthelmintic products (dewormers) and the feed-through and mineral forms of Safeguard perform quite well.
Newcomb says every animal may not ingest the same amount of feed-through formula due to the normal jostling in the pasture. However, what does happen is the general population of cattle in that pasture is treated and the worm population is “strategically” reduced.
Benefits of combining classes of medicines
“For that first deworming, we recommend that ranchers use at least two of the three anthelmintic classes available in the U.S. concurrently,” Newcomb says.
There are 3 classes of worm medicines in the U.S., he explains.
- Benzimidazoles, such as Safe-Guard®, albendazole, and oxfendazole
- Macrocyclic lactones, such as doramectin, ivermectin, moxidectin or eprinomectin
- Imidazothiazoles, such as levamisole (trade name Prohibit) and morantel tartrate
“We know that by using two or more of these classes of medications concurrently, we can extend the life of all three classes of anthelmintic. If you build resistance to one drug in a class of drugs it won’t be long before you’ll have resistance to all drugs in that class.” Anthelmintic resistance is an emerging problem in the U.S. cattle industry that will have to be addressed sooner rather than later.
No treatment may mean less gain
Not treating livestock for internal parasites can cost ranchers money in unrealized weight gains. “You may see a decrease in weaning weights or the calf won’t be able to reach its full genetic potential. In the herds where we’ve strategically dewormed, we’ve seen increases in weaning weights anywhere from 25 to 40 pounds,” he says.
“Adult cattle that have been strategically dewormed will have seen an average of about 10 percent improvement in conception rates. Strategic deworming can help get more cattle bred and result in heavier calves,” Newcomb says.
What internal parasites do to livestock
Internal parasites decrease feed intake. It is the largest single effect parasites have on animals. You can see the decrease in feed intake in every segment of the cattle production system. Cow-calf, stocker, or feedlot, parasitized cattle actually eat less and, if the animal is consuming less, then weight gains are going to suffer. “You’ll see decreased consumption of forage or feed in a parasitized animal. The parasitized animal actually eats less than one that is non-parasitized,” Newcomb says.
Internal parasites also affect the ability of livestock to respond to vaccines. “Therefore, it’s important to deworm these animals and vaccinate when the cattle are as free of parasites as possible.”
Physical clues to parasitism are decreased appetite, slower weight gain and reduced conception rates. When signs such as poor body condition and rough hair coats are evident, the parasite load has become significant and production and economic losses have already occurred.
The preferred environment of internal parasites
Gastrointestinal parasites like warm, humid, damp environments. They do not like hot, dry, arid areas. “Where you find moisture, that’s where you’ll find the parasites. Even in periods of drought, you can still get fairly heavy parasite loads because cattle tend to graze where the grass is lushest, such as along streams or creek beds where the moisture would be. Also, in a drought, livestock are more susceptible to the parasites because of the nutritional stress of the drought,” Newcomb says.
Consult with your veterinarian to determine what parasites to strategically target and which classes of medication and delivery methods will work best for you.
Tests such as the fecal egg count reduction test will indicate if the strategy is working.
“The older the animal gets, the more immunity it has to parasites. But because of nutritional or environmental stress, or because of their genetics, I suggest that ranchers strategically deworm animals to lower the parasite burden on the pasture as well as in the animals. When you do treat for internal parasites, follow up on the cattle by doing a fecal egg count reduction test, to make sure that whatever you used worked.”
A Strategic Approach to Reducing Internal Parasites is excerpted from the April 2018 issue of The Cattleman magazine.