Raising livestock means dealing with parasites. Although parasites cannot be completely eliminated, good treatment protocols keep them at bay.

“We know parasite burdens have a large impact on production,” said veterinarian Dr. Carling Matejka. “They truly are silent profit thieves. Having a large parasite load can impair immune function because the immune system is focused on ‘treating’ the parasite, making cattle more susceptible to other infections.”

Infected cattle typically have lower conception rates and reduced feed efficiency. Because parasites use some of the nutrients intended for cattle, more feed is necessary to achieve the same weight gain compared to cattle without significant parasite loads.

Parasite burdens can result in economic losses. The biggest impact is from gastrointestinal parasites such as roundworms, although lungworms, flukes, tapeworms, cattle grubs, ticks and lice are also profit thieves. Coccidia, Giardia and Cryptosporidium can be problematic but are more common in calves.

“We see signs of reduced appetite, depressed weight gain, poor feed efficiency, lower reproductive rate, diarrhea and bottle jaw,” said Matejka, reviewing common indicators of parasite infection. “A lot of these signs are subclinical, so sometimes it’s hard to notice changes in the herd.”

The goal of managing internal cattle parasites is minimizing the use of dewormers to maximize health and production.

A common misconception is that cold weather kills parasites, but that isn’t the case. Parasite larvae can overwinter in the pasture and infect cattle in spring and summer. Spring is a good time to begin a focused parasite management program, especially for cattle that will be turned out to pasture.

Categorize pastures as high or low risk to manage cattle groups more effectively. High risk pastures are wet and cooler during spring and summer. Overgrazed or overstocked pastures, autumn-grazed pastures used in spring and pastures grazed by youngstock are also high risk. Higher parasite levels in these pastures require more aggressive management.

Low risk pastures are usually dry and have been grazed once during the growing season. Areas tilled during summer and left to rest are also low risk. Consider rotational grazing to allow pastures ample rest time before cattle return.

Fecal egg counts (FECs) estimate the number of parasite eggs present and can aid in making deworming decisions. Cattle FECs should be done four weeks following pasture turnout and again in autumn. FECs for calves can be done at weaning, and new cattle should have a FEC done on arrival.

FECs can be done on individual animals or on pooled samples. Producers should work with their herd veterinarian to determine the most efficient method for sample collection and to develop an effective treatment plan.

Because cattle have been routinely dewormed with the same products for many years, parasites have developed resistance to some anthelmintics. It’s important to select a product (or two) that will be most effective for the herd.

A combination treatment using two different classes of dewormer administered at the same time might include pour-on ivermectin and a drench using a white dewormer. Matejka said while this isn’t the most cost-effective plan, it will improve treatment rate and reduce resistance.

Keep in mind the 80/20 rule: 80% of the parasites are carried by 20% of the animals. Leaving some animals untreated will help delay resistance. Determine which animals can remain untreated by considering the body condition score (BCS). On a nine-point BCS scale, a score of 5 is ideal. Lower scores indicate thinner animals, so with the 80/20 rule, thin and moderate cows would be treated and obese cows would remain untreated. Thin cows that are consistently high shedders or have trouble maintaining weight should be culled.

A 90% reduction in parasite eggs is considered effective treatment. Producers who want to evaluate treatment effectiveness can have a fecal egg reduction test done 10 to 14 days following treatment.

External parasites such as lice, chorioptic mites (mange), flies (horn, stable and houseflies) and ticks are problematic for cattle. Ticks can carry blood-borne illnesses such as anaplasmosis and babesiosis. Flies carry other diseases, such as pinkeye, that limit herd production.

Signs of external parasites vary. Inspect cattle closely for parasites, and watch for

itching, stress and irritability, changes in grazing behavior, hair loss and production losses.

Be mindful that external parasites are not the only cause of hair loss. If treatment doesn’t appear to be working, it’s possible parasites aren’t the main problem. Nutritional deficiencies including insufficient dietary zinc, copper and vitamin A can result in hair loss. If animals have had a fever, hair follicles enter a resting phase, leading to temporary hair loss.

Managing external parasites begins with identifying the pest. “Lice are hard to see, but take the time to look for them. Part the hair,” said Matejka. “Flies are always present but determine whether they’re a problem.”

Flies and ticks are seen mostly in pasture conditions and during warmer months. Lice and mange are more likely present in confinement housing during cooler months.

Matejka urged producers to work with their veterinarians to develop treatment plans. Check labels on endectocide products to make sure the target pest is on the label and follow up with a second treatment if indicated.

Weigh several animals to get an idea of weights and adjust dosing appropriately. “Pour onto clean, dry skin,” said Matejka. “Make sure to pour onto the correct areas. When treating for biting lice, pour across the animal’s entire back.”

Sucking lice bite and ingest blood along with the product absorbed by the cow. In contrast, biting lice travel over the animal and must move through the product to be killed. Pouring in one spot is not sufficient to kill biting lice.

Treat cattle groups that have pests present or are at high risk for parasites. Rotate insecticide treatments from year to year to reduce resistance. A follow-up treatment applied according to the product label will ensure newly hatched pests will be killed. Use products with caution to avoid resistance.

Reduce the risk for external parasites with proper manure and water management, including eliminating old feed and carcasses. Use fly control in sheds and buildings.

Work with the herd vet to develop a good parasite management strategy. Use all products according to product label and animal weight. Don’t apply endectocides to snowy, wet or manure-covered hair. Avoid unnecessary treatment, rotate insecticide classes and avoid overstocking and overgrazing. Quarantine and inspect any new animals for external parasites and treat them prior to adding them to the herd.

by Sally Colby