Flies, ticks and other external parasites on cattle cause stress, reduce weight gains and transmit disease such as pinkeye and anaplasmosis. This is not breaking news, but with antibiotic use coming under increasing scrutiny and regulatory action, producers can benefit by focusing more on parasite control and less on medicated feeds for dealing with diseases.
Oklahoma State University livestock entomologist Justin Talley, says external parasites cause enormous economic losses to the cattle industry. Horn flies lead the way, causing an estimated $1.36 billion in annual losses in U.S. livestock herds. Stable flies cause an additional $672 million in losses, followed by horse flies at $296 million, face flies at $191 million and ticks at $162 million.
Talley says when horn flies are present, control efforts can bring an average of 1.5 lb. of extra gain per week. Generally, 200 to 300 flies per animal constitutes an economic threshold for treatment.
Stable flies tend to accumulate on the lower part and legs of the animal, with five to 10 flies per leg as a typical economic threshold. Populations typically peak in the spring and again in the fall.
Face flies are not a biting fly, but cause stress and play a role in transmission of Moraxella bovis, the pathogen that causes pinkeye.
Horse flies and deer flies can serve as mechanical vectors for anaplasmosis. Gregg Hanzlicek, at the Kansas State University Veterinary Diagnostic Laboratory, says flies carry, but don’t amplify the anaplasmosis pathogen, meaning the bacteria flies pick up when feeding is the maximum they will be able to pass on to the next animal. Control is important though, as flies can travel significant distances and introduce anaplasmosis into beef herds.
Several species of ticks, particularly the dog tick, serve as biological vectors for the anaplasmosis pathogen. When ticks feed on a positive animal, the bacteria establish inside the tick and reproduce, and the concentration can reach very high levels. When the tick feeds on an animal it will pass those bacteria through the saliva.
Fly control efforts should begin early in the season, before populations explode. Talley says to avoid pesticide resistance, don’t use pyrethroid tags more often than one year in three, and do not use organophosphate tags more than two years in a row.
Insect growth regulators (IGRs) and larvicide are found in mineral blocks or mixes. They pass through the animal and kill or inhibit fly larvae in the manure. Use these products in the early spring to match the time flies begin laying eggs.
The cost of insecticide ear tags average $3.20 to $4.45 per cow per season. Pour-on products range from $2.50 to $9.50, depending on the number of treatments needed. Generally, Talley says, ear tags combined with an IGR provide cost-effective control.