“We’re already starting to see a heavier-than-normal worm load in pastures across Texas,” says John Davidson, DVM, senior associate director of beef professional veterinary services, Boehringer Ingelheim. “Combine that with the fact that it’s been a hard winter for cattle, with many fighting muddy and wet conditions since fall. Deworming cattle this spring will be important in reducing production losses and improving overall animal health.”
“Conditions in our area are particularly severe this year, after a fall explosion in armyworm populations caused severe damage to not only crops but also pastures,” adds Michael Allen, cattleman and DVM with Houston County Veterinary Hospital, Crockett, Texas. “As a result, there is almost no standing forage left anywhere this winter, and it will take a while for pastures to regrow. In these conditions, cows are forced to eat closer to the ground, making them more likely to ingest worms.”
Stealing from the herd
“It’s hard to recognize symptoms of internal parasites, especially in adult animals,” Dr. Davidson says. “They steal from you under the table, since so many of the early signs are subclinical.
“The most common visual signs are fairly subtle: cattle that just don’t look healthy, may be slightly thinner, and have a rough hair coat,” he continues. “At that point, production losses are probably already significant.”
Dr. Davidson says internal parasites can negatively impact cattle health and production in several important ways:
Reduced feed intake. Heavy worm loads cause cattle to eat less, which slows weight gain and cuts feed efficiency.
Weakened immunity. Internal parasites can have a major impact on an animal’s immune system, due in part to poorer nutrition. This can lower the animal’s ability to fight off infections and reduce the effectiveness of vaccinations. In addition, some parasites actually hinder the animal’s defense mechanisms. For example, the Ostertagia ostertagi (brown stomach worm) secretes substances that suppress the animal’s immune system, which can interfere with its ability to respond to vaccines.
Reduced reproductive efficiency. Serious worm loads can lower conception rates in cows and weaken semen production in bulls because their higher hormone levels can actually depress immunity to parasites.
Less milk produced for calves. Deworming cows prior to calving ensures that they’ll be able to maximize feed intake for milk production.
“All of these can add up to major losses in a herd,” Davidson adds. “Research shows that, compared to all other herd health practices, including the use of implants and antibiotics, treating for parasites delivers the largest economic return.”
Right time and product
The key to effective parasite control is to break their life cycle. “In the southern United States, worm species typically go dormant in the cattle’s stomachs over summer, so the best time to control them is while they’re still active in May or June,” Dr. Davidson points out. “In the northern part of the country, worms such as the brown stomach worm can overwinter in cattle, so early fall is the most effective time to deworm the herd.”
Dr. Allen says many of his clients will use a pour-on product this spring, due to the convenience and added fly control ahead of summer. “Other ranchers prefer an injectable product, and some use a combination; one product for cows and another for calves. Choosing the best product depends on the individual operation and how they do things.”
“It’s also important to make sure you choose a deworming product that is effective at both larval and adult worm stages,” notes Dr. Davidson. “That way, you’ll know you’re getting broader protection.”
Drs. Allen and Davidson encourage producers to work with their veterinarians to create a deworming program best suited to their operation’s specific needs.