Dave Barz: Battling external parasites in cattle | TSLN.com

Dave Barz: Battling external parasites in cattle

Dave Barz, DVM

Most of the storms have missed our area, but others have been pummeled severely. The cool, wet weather has really delayed the spring fly hatch, but with the warm days to come, I’m sure the populations will increase rapidly. Before the peak season arrives, it is important to develop an external parasite program for the summer.

External parasites cause monetary losses in most operations that are very difficult to quantify. The cattle are restless and don’t graze or go to the bunk as producers would like. This results in decreased weight gains and milk production. Many of these parasites are blood feeders and are an important vector in the transmission of diseases within the herd and to adjacent herds. Studies have shown the presence of flies on cattle during the summer can cause an average of 4 percent reduction in weaning weights. The most common parasites are flies, lice and ticks.

During cold mornings, horn flies can be found on an animal’s back trying to stay warm. As the heat of the day increases, the flies move underneath the animal for protection and to digest their blood meal. These animals feed 20-30 times per day. Anytime a cow has more than 200 flies present it is deemed a problem. In some herds with no fly control, bulls may have as many as 10,000 flies present. The bull’s testosterone levels seem to attract flies and their thick necks make it a problem for them to combat their presence. During a single season up to 10 generations of horn flies may be produced and they have been able to migrate at least three miles per day in the wind.

The fly tag has helped control fly populations. It should be applied in late May or early June when fly populations reach about 200 per animal. This late-spring tagging ensures the tags will still have adequate insecticide late in the season. In southern climates, cattle may be tagged in early spring and then retagged in August. We recommend rotating insecticide types yearly to ensure no resistance is built up in fly populations.

Pour-ons have been used for many years. Most of these products advertise thirty days of effectiveness. We see the results begin to decrease in 2-3 weeks. Most of these products are designed to remove lice, but work well on flies. Check all available products and the duration of their effectiveness. Some of these pour-ons used at turnout are also effective in decreasing internal parasite populations.

Sprays and dusters have been used for many years. Once the cowherd becomes accustomed to the procedure, cows will cooperate willingly. It is best to use sprays with good residuals, but it will probably be necessary to re-spray every 2-3 weeks.

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Dust bags and back rubbers are very useful. The same insecticides used in sprays are incorporated into these units. These dispense products to individual animals. It is important to be sure they are always well stocked. Because it is an individual preventative or treatment, it is important to have these products out long before peak fly populations and not as a reactionary measure.

Products may be fed in mineral. IGR passes through the animal and remains in the manure patty. This chemical prevents the maturation of fly larvae in the pasture, but remember, flies can migrate several miles per day. If a hatch is decreased in your pasture, the neighbor’s flies may find a new home with your herd.

External parasites need to be controlled in cattle operations. Not only are efficiency and weight gains decreased, but they also serve as a vector for diseases. Your veterinarian, extension livestock specialist, or nutritionist can help devise a parasite program which requires minimal handling of the herd with good residual control. Careful planning and implementation will increase the efficiency of the herd while increasing animal comfort during the hot days of summer.

Most of the storms have missed our area, but others have been pummeled severely. The cool, wet weather has really delayed the spring fly hatch, but with the warm days to come, I’m sure the populations will increase rapidly. Before the peak season arrives, it is important to develop an external parasite program for the summer.

External parasites cause monetary losses in most operations that are very difficult to quantify. The cattle are restless and don’t graze or go to the bunk as producers would like. This results in decreased weight gains and milk production. Many of these parasites are blood feeders and are an important vector in the transmission of diseases within the herd and to adjacent herds. Studies have shown the presence of flies on cattle during the summer can cause an average of 4 percent reduction in weaning weights. The most common parasites are flies, lice and ticks.

During cold mornings, horn flies can be found on an animal’s back trying to stay warm. As the heat of the day increases, the flies move underneath the animal for protection and to digest their blood meal. These animals feed 20-30 times per day. Anytime a cow has more than 200 flies present it is deemed a problem. In some herds with no fly control, bulls may have as many as 10,000 flies present. The bull’s testosterone levels seem to attract flies and their thick necks make it a problem for them to combat their presence. During a single season up to 10 generations of horn flies may be produced and they have been able to migrate at least three miles per day in the wind.

The fly tag has helped control fly populations. It should be applied in late May or early June when fly populations reach about 200 per animal. This late-spring tagging ensures the tags will still have adequate insecticide late in the season. In southern climates, cattle may be tagged in early spring and then retagged in August. We recommend rotating insecticide types yearly to ensure no resistance is built up in fly populations.

Pour-ons have been used for many years. Most of these products advertise thirty days of effectiveness. We see the results begin to decrease in 2-3 weeks. Most of these products are designed to remove lice, but work well on flies. Check all available products and the duration of their effectiveness. Some of these pour-ons used at turnout are also effective in decreasing internal parasite populations.

Sprays and dusters have been used for many years. Once the cowherd becomes accustomed to the procedure, cows will cooperate willingly. It is best to use sprays with good residuals, but it will probably be necessary to re-spray every 2-3 weeks.

Dust bags and back rubbers are very useful. The same insecticides used in sprays are incorporated into these units. These dispense products to individual animals. It is important to be sure they are always well stocked. Because it is an individual preventative or treatment, it is important to have these products out long before peak fly populations and not as a reactionary measure.

Products may be fed in mineral. IGR passes through the animal and remains in the manure patty. This chemical prevents the maturation of fly larvae in the pasture, but remember, flies can migrate several miles per day. If a hatch is decreased in your pasture, the neighbor’s flies may find a new home with your herd.

External parasites need to be controlled in cattle operations. Not only are efficiency and weight gains decreased, but they also serve as a vector for diseases. Your veterinarian, extension livestock specialist, or nutritionist can help devise a parasite program which requires minimal handling of the herd with good residual control. Careful planning and implementation will increase the efficiency of the herd while increasing animal comfort during the hot days of summer.

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