“The healthier the cattle are, the better the immunity is, the better the calves will do and the more satisfied my client is,” says Ted Cundiff, DVM, a veterinarian in Richmond, Kentucky.
As a stockyard veterinarian and stocker veterinarian, Cundiff has the opportunity to help thousands of calves each year be sure their next step in the marketing channel is a healthy one. That includes taking care of details like controlling horn flies during the summer months and lice in the winter.
On both counts, he explains, “The problem isn’t going to go away. There aren’t a lot of management tools other than a good treatment program and a good retreatment program.”
A handful of flies cost plenty
In the case of horn flies—blood feeders that take 20-30 meals per day—there’s no eliminating them, but there is trying to minimize the estimated $700 million to $1 billion economic loss they cause the industry each year.
“Manage horn flies and you’re probably going to add an extra 10-15 lbs. to the calf during its life,” Cundiff says.
Depending on the research you consider, controlling horn flies in the stocker pasture can be worth 15-50 lbs.
In studies at the University of Nebraska (UN), calf weaning weights were 10-20 lbs. heavier when horn flies were controlled in the mama cows. According to other studies there, horn flies caused reductions in yearling weights of grazing cattle by as much as 18%.
UN researchers explain the economic injury level for horn flies is 200 flies per animal. That’s about how many that fit in the space of your outstretched hand. Horn flies leave hosts only to deposit eggs in fresh manure pats or to find other hosts.
Losses come mostly from decreased performance. According to researchers at the University of Florida (UF), in the Extension publication, Horn Fly Management, the irritation and blood loss associated with horn flies can cause 0.30-0.50 lbs. of weight loss per day.
“Although an individual horn fly only consumes 1.5 mg of blood per meal, horn flies take many meals per day, and large populations may cause substantial blood loss,” say Philip Kaufman, extension entomologist and Emma Weeks, assistant research scientist at the University of Florida.
Drivers of economic loss associated with horn flies stem from disrupted and decreased grazing, as well as more energy spent traveling and tail switching in an effort to get rid of the pests.
Plus, UF researchers say, “Irritation of the skin due to high numbers of horn fly bites in small areas may cause open wounds, which can increase the risk of secondary infections. The bite lesions, particularly if infections develop, may lead to damaged hides and potentially reduce hide values.” They add that horn flies also are suspected of mechanical transmission of anaplasmosis, anthrax and other disease-causing pathogens within herds.
Horn fly interventions include insecticide-impregnated ear tags, concentrated pour-ons, dust bags and oral larvicides.
Several years ago, Cundiff began using StandGuard®, containing gamma-cyhalothrin, a third-generation pyrethroid applied directly to the backs of cattle.
“Every generation gets a little better in its efficacy of fly knockdown and kill quality,” Cundiff says. “Resistance is also less likely with the newer products. If you’re using an older-generation pyrethroid, I think it would be good to upgrade to a newer one and see if it won’t help you.”
Cundiff was looking for a product to fill what he considered a void in his processing program a few years ago. He tried StandGuard based on a peer’s recommendation.
“I feel like it has filled the void,” Cundiff says. “Since I started using it, I’ve put it on practically every calf I’ve processed.”
Cundiff also mentions he likes the fact that there are two doses for StandGuard—one for cattle weighing 600 lbs. and more and one for cattle weighing less than that.
Lice add to cold weather impacts
“In my operation, I use it year-round,” Cundiff says. “In late winter and early spring, we get a lot of lice and with this we’re doing a really good job on lice. StandGuard is labeled for a one-time, season-long treatment, and I suspect it’s doing that because we don’t get any complaints about lice.”
Similar to horn flies, sucking lice puncture the skin of host animals to take their meals. Biting lice scrape and irritate the animals’ skin. Drivers of economic loss associated with them include reduced average daily gain and weaning weights, decreased feed efficiency and increased susceptibility to disease.
“Infestations of biting and sucking lice have been associated with reduced weight gains and general unthriftiness of cattle. The economic impact of these small insects has been very difficult to assess. However, it appears that an average of 10 or more per square inch are necessary to have a significant effect,” says Lee Townsend, Extension entomologist at the University of Kentucky, in Lice On Beef and Dairy Cattle. “Moderate to heavy infestations add to the impact of cold weather, shipping stress, inadequate nutrition, or harm from internal parasites or disease. The interaction between low levels of both lice and intestinal nematodes can reduce weight gains by more than 8%. The energy that lice ‘steal’, coupled with other factors, can have a severe impact on animal health. Manifestations can be anemia, slow recovery from diseases, poor gains, or general unthriftiness.”
Lice are primarily spread from animal to animal.
“Lice can travel in on new cattle,” Cundiff says. ”Any time you bring in new cattle, you need to be persistent about treating them.”
More specifically, Townsend says, “In enterprises where animals are added to the inventory on a regular basis, it is best to assume that all purchased animals are infested. They should be isolated from the resident animals until their full course of treatment is completed. Cross fence contact can be sufficient for spread of these insects, especially during the winter when louse burdens are greatest.”
Lice spend their lives on the host animal. According to Townsend, sucking lice typically die within a few hours of being removed from the host. Biting lice, he says, can live up to a few days off the host, under ideal conditions.
“A high-energy diet seems to reduce the effects of cattle lice on weight gains, perhaps because lice populations decline on better-fed cattle,” Townsend says. “A sound feeding program and high energy ration serves as the foundation of a louse control program.”
Lice interventions include insecticide sprays, pour-ons and dust.
“As soon as summer comes, the lice begin to disappear and you get all kinds of horn flies. So, I use StandGuard in the in the summer and early fall for horn flies, and I use it in the winter and early spring for lice,” Cundiff says.
“I feel like when these cattle go home, the owner is going to see a calf that slicks up, doesn’t have any lice in the wintertime or as many horn flies bothering them in the summer,” Cundiff says.
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