Bugs can have a severe impact on cattle

Gary Sliworsky
Ag. Rep.

Biting and blood-sucking insects can have a powerful, often underestimated impact on cattle grazing behavior and the health of rangelands, according to a livestock parasitology expert.
The behaviour of cattle can change dramatically as a result of attacks by mosquitoes, biting flies and other pests, says Dr. Doug Colwell of Agriculture and Agri-Food Canada’s Lethbridge Research Centre. Behavioural changes not only affect herd health and productivity, they carry major implications for the health of grasslands.
“Biting flies in particular can cause physiological and behavioural changes that influence what cattle eat and where they congregate in a pasture. This animal response can have a profound impact on grassland utilization and the health of plant communities,” says Colwell. He reported that livestock researchers have documented striking examples of how biting and blood-sucking insects affect grazing animals. Caribou swarmed by mosquitoes will head to wind-swept hilltops or onto snowy ground for relief, while feral horses have been observed to move onto windy beaches. Respite comes at a price - little if any forage is available in such environments, and its palatability and nutritive value are often minimal.
The impact of biting and blood-sucking insects on cattle has long been considered a herd-health problem, he says. Animals can suffer blood loss, toxic reactions, allergic reactions and sheer exhaustion, along with heat stress that results when the cattle bunch together. The nature and severity of these problems depends on the fly species and the intensity of the attack.
However, in recent years, researchers have discovered that insect attacks have more subtle effects on grazing animals, by triggering the production in the brain of powerful proteins and hormones - neuro-chemicals, such as opioid peptides and serotonin-related compounds.
Colwell explains that these neuro-chemicals regulate many physiological and behavioural reactions to stress. This influences such things as memory and learning, anxiety, feeding behavior and appetite, along with avoidance behavior, social interaction, reproductive behavior, and immunity and resistance to disease.
“Animals learn where to find better quality forage from their herdmates,” says Colwell. “If they’re under attack from biting or blood-sucking insects, their ability to learn from herdmates and to remember where they can find better quality forage can be impaired, so there could be important implications for animals that return to the same pasture year after year.”
The consequences for ranchers can be economically significant, he says. If cattle avoid areas where they were attacked in the past, for example, they might alter their grazing patterns substantially, creating serious undergrazing or overgrazing management issues. Such changes in grazing habits could also have significant environmental consequences for wildlife, riparian zones and waterfowl habitat.
There are few control options for rangeland insects, he says, but further research and development is leading toward promising integrated pest management strategies.