In a previous Update article (Feb ’24), I discussed some of the reasons that a large number of cows did not breed back and were identified as “open” during routine fall pregnancy diagnosis. The number of non-pregnant cows ranged from 20 to 40% and even 50% in one anecdotal report. Stressors discussed included: vibriosis and trichomoniasis (not common), Canadian smoke, snow-wind-cold winter conditions, uncontrollable infestations of blood sucking horn and stable flies, and face flies that feed on tears and muzzle fluids. Not only do face flies feed on fluids, but they are a problematic vector for spreading pinkeye (Moraxella bovis) from animal to animal.
Difficult and uncontrolled fly infestations have a negative effect on reproductive performance due to the persistent horn fly blood sucking and annoying face flies. Economic losses due fly infestations range from 4 to 15% reduction in weaning weight. To put this into perspective using an 8% loss in weaning weight for example, a steer calf with the genetic potential to wean at 600 lb. could give up 48 lbs. in weaning weight due to blood sucking horn flies, face flies, and stress. The difference in value between a 556 lb. weaning weight and a 600 lb. weaning weight, factoring in the price slide between the two weights in today’s market environment, is a potential loss of approximately $21/steer.
The horn fly life cycle is short. After breeding, female horn flies lay eggs in cattle manure that is fresh. Temperature plays a role in the rate at which the eggs hatch. During the life cycle, eggs hatch and the immature larvae develop while feeding in the manure patty; finally pupating into flies that can travel significant distances searching for a blood meal host. It takes between 10 and 20 days from the time fly eggs are deposited in the manure until the young fly begins its search for a suitable host. Face flies have a similar life cycle, but the generation interval is longer requiring two to three weeks. The economic horn fly threshold, when significant damage occurs in beef cattle, is estimated to be 150-200 flies per animal. The advent of insecticide impregnated ear tags usher in a simple and efficient method for the control of horn flies. Unfortunately, the generation interval of less than two weeks and as much as 10-12 fly generations per season creates a perfect environment for insecticide resistance. Stable flies, on the other hand, are blood feeders that often feed on the front legs of cattle and horses, and the bites are very painful. Unlike horn and face flies that have life cycles in fresh manure, stable fly females deposit eggs in decaying organic material in feedlots and pens along fences, posts, feed bunks, and hay and straw stacks.
There are multiple methods for fly control:
1. Insecticide impregnated ear tags. Compounds used in ear tags include synthetic pyrethroids, organophosphates, combinations of the pyrethroid and organophosphate compounds as well as macrocyclic lactones. Some ear tag products also include piperonyl butoxide as a synergistic booster to enhance fly toxicity. For effective fly control with ear tags, it is recommended that the tags are not installed too early in the fly season, removed soon after the first killing frost, and insecticide chemical classes are rotated annually to ensure the same product is not used two seasons in a row. Unfortunately, in some situations chemically impregnated ear tags have become ineffective due to fly resistance.
2. Individual animal self-treatment is an alternative fly control method that includes dust bags and back rubbers mounted in high traffic areas around water and mineral sources. Dust bags contain insecticide dust and back rubbers contain similar insecticides added to mineral oil or diesel fuel that keeps the twisted fabric impregnated with the insecticide mixture.
3. Insecticide spray solutions are another alternative method for large groups of cattle delivered using a power sprayer (150-200 psi) that delivers an insecticide mixture for effective overall coverage of body and legs where blood sucking stable flies feed. For smaller groups of cattle two-gallon hand-held sprayers can be used to spray backs and legs effectively, when cattle are in a fairly tight group.
4. Medicated mineral treated with growth regulating compounds and larvicides. Examples of growth regulating compounds used in mineral mixes are diflubenzuron and methoprene, which interfere with fly maggot development whereas the larvicide tetraclorvinphos kills fly maggots in fresh manure. Medicated minerals are effective provided cattle readily consume treated mineral mixes. However, variable response can occur when treated cattle graze pastures adjacent to herds of cattle where flies are not being controlled.
5. Pour-On insecticides containing ivermectin are an effective method for controlling external and internal parasites controlling gastrointestinal round worms, lung worms, grubs, horn flies, sucking and biting lice, and sarcoptic mange mites. Fly control will last 2-4 weeks.
Fly populations have developed resistance to insecticide-impregnated fly tags due to the short fly generation interval and multiple generations in a normal summer fly season. Effective fly control measures center around using a combination of methods, which will be more effective than relying on a single treatment method.
