Control Pests to Improve Production

 Article courtesy of Justin Talley - Oklahoma State University

 Arthropod pests limit production in the goat industry in many ways. External parasites feed on body tissue such as blood, skin and hair. The wounds and skin irritation produced by these parasites result in discomfort and irritation to the animal. Parasites can transmit diseases from sick to healthy animals. They can reduce weight gains and milk production. In general, infested livestock cannot be efficiently managed.  In this article we focus on the Summer’s common pest “Flies”.

Flies
Flies go through complete metamorphosis which consists of eggs, larvae, pupae and adults, with each life stage occupying different habitats (Figure 11). Flies particularly troublesome to goats include horn fly, stable fly, horse flies, house flies, blow fly, mosquitoes and black flies. These flies can be severely annoying and may affect the performance of goats. They hinder grazing and cause goats to bunch or run to get relief from the annoyance of these flies. Biting or blood-sucking flies can cause painful bites and significant irritation to goats.

Biting Flies
Horn Flies
Horn flies are primarily a pest of cattle, but occasionally seen on goats, especially when goats are co-grazing a pasture with cattle. Both male and female horn flies take blood from the host and feed from 20 times to 30 times a day. Horn flies continually stay on the animal and only leave the animal for short periods to lay eggs. Typical feeding areas on goats include the back, side, belly and legs. Horn fly populations begin building up in the spring and last until the first frost.

Stable Flies
Stable flies are medium-sized flies, which resemble house flies. Stable flies feed on goats with their head up, and prefer to stay on the feet and legs of goats. Both male and female stable flies take blood from the host and have a very painful bite. Large populations of stable flies on pastured goats often cause goats to bunch and mill around. Stable fly larvae develop in moist decaying organic matter associated with spilled feed, soiled hay or straw bedding. They particularly like areas where hay bales were fed and the hay is trampled into the ground by feeding goats. Stable flies are more of a problem around barns or loafing sheds, where there is an abundant resource of decaying organic matter for them to develop in as well as vertical resting sites such as the sunny sides of barns or sheds.

Horse Flies and Deer Flies
There are many species of horse and deer flies (Figure 14) in U.S. Seven or eight species can be considered significant pest, depending on the location. Horse flies vary in size from ½-inch to 1.5 inches or longer. Female horse flies are vicious biters, and peak populations of one species or another occur throughout the summer months. Male horse flies do not bite. Horse and deer flies generally only complete one generation per year. Many horse flies lay their eggs around the edges of ponds and their larvae develop in the moist mud along the perimeter of the pond, making control in the larval stage impossible. Some of the most important species lay their eggs in the soil under thick layers of leaves in the heavily timbered areas. Larvae develop in the soil. Adult horse and deer flies prefer feeding on the legs and backs of animals. Heavy populations of adult horse flies can cause economic losses, but controlling them in a cost effective manner is not possible. Because the female horse fly is only on the animal for a few minutes while taking a bloodmeal, it is difficult to get enough pesticide on the animal to deter the fly from feeding. The flies may receive enough pesticide to kill them after they leave the animal, but this is difficult to determine. Because horse flies are continually emerging throughout the summer and many species have an extensive flight range, there will be flies on goats regardless of whether or not a pesticide treatment has eliminated some of the population. Horse flies are repelled by some pesticides just after spraying the animal, but this is not a practical method of protection. Recently, traps have been promoted to decrease populations of horse flies, but these traps are expensive and numerous traps are required to reduce horse flies in a relatively small area.

Mosquitoes and Black Flies
Certain species of mosquitoes and black flies species will feed on goats, but are normally not present in high enough populations for a long enough period to cause significant damage. Both of these groups of insects are most prevalent in the spring. Black fly immature stages develop only in running water in streams or rivers. Large populations sometimes occur in late spring and into early summer. Mosquito larvae develop in standing water and pest populations on goats are most often associated with water from flooding or heavy rainfall that remains for a week to ten days. Large populations sometime occur in pasture areas that hold temporary pools of water. The primary threat from mosquitoes is their ability to transmit disease.
 
Nuisance Flies
House Flies House flies do not bite goats, as they only possess sponging mouthparts. However, they may cause extreme annoyance to animals when they are present in large numbers. House flies tend to aggregate on specific areas of the animal and can be severe nuisance pests of confined animals, especially goat kids. They often aggregate around the eyes and mouth because of the moisture secreted by the animal. House fly larvae develop in moist decaying organic matter, especially accumulated manure, rotting feed and garbage. House flies will utilize areas associated with spilled feed and hay to lay eggs similar to the life cycle of stable flies. House flies are not often pests of pastured goats unless such goats frequent loafing sheds. Good sanitation around barns is the best method of house fly control. Sprays inside buildings, referred to as premise sprays, can also be utilized to control adult house flies. Premise sprays can be used on surface areas inside of barns, where the flies will contact the insecticide residue when resting on these surfaces. Automated mist blowers can be used in barns to apply space sprays which will kill adult flies. Commercial baits can also be used to attract house flies to bait containing a pesticide. Baits typically attract only house flies and do not provide control for other fly species.
 

Blow Flies
Blow flies are similar to house flies and do not bite goats, but cause significant annoyance to the animals and animal operators. They tend to aggregate on animals with wounds or skin infections. Blow fly larvae develop in decaying organic matter and decomposing dead animals. The primary source of blow fly attraction to animals is bacterial activity on the animal. Sanitation around barns is the best method of preventing a blow fly population from becoming significant. Special care should be taken during kidding season to clean up afterbirth, since this is highly attractive to blow fly populations.
 
Control of Flies
A significant portion of fly problems around livestock buildings can be alleviated through sanitation and proper manure management. This will be unsuitable for fly production. Regular removal of bedding material and spilled feed is a good way to prevent fly populations from becoming significant.
The utilization of fly parasitoids sometimes known as ‘fly predators’ works well in combination with a good sanitaion program. Several companies produce and market these parasitoids to livestock operators and can be cost effective when used properly. These parasitoids are small wasps that target lay their eggs inside the fly pupae. Proper dissemination is critical to preventing a fly outbreak, and the best practice for these ‘fly predators’ to be successful is the practice of releasing these before fly populations become noteworthy. If fly parasitoids are utilized, insecticide use should be limied. Insecticides kill parasitoids just like it does flies.
Insecticide-based control may be necessary when flies become extensive around goat operations. The only products approved for on-animal application to goats are permethrin or pyrethroid-based products, with best results from synergized pyrethroid products containing piperonyl butoxide (PBO). Goat operators have more options when just treating the barns and these are sometimes referred to premise sprays. The best option for a premise spray is to use a residual spray that remains effective for some length of time, compared to a non-residual product such as pyrethrum. When applying residual sprays, be sure to treat vertical fly resting sites such as barn walls. Make sure the surface is not wet or greasy when applying the product. Recently, more livestock operators who house animals in barns for the majority of the time are utilizing automated mist systems. These can be effective, but care should be taken not to over apply products, especially when animal feed or hay is present. The overuse of these systems also can lead to insecticide resistance. Goat operators with these systems should set these to be active when the flies are active.
 
Summary
A comprehensive management plan for external parasites on goats will be variable and unique to individual goat operations. The key to a successful parasite management program is continual monitoring of the herd. The combined approach of an integrated pest management program is the most economical and environmentally sound tactic. The overall goal of a sound external parasite program is to manage the pests in a manner that reduces stress to the animals, as well as reduce the risk of pathogen transmission from the parasites.