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Controlling Cattle Parasites

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Updated February 2018

As we manage the cow herd into the fall and through the winter, our primary focus should be on health and nutrition. These two areas of management determine reproductive performance, which is the number one factor that affects profitability. Assuming that an effective immunization program minimizes the probability of disease, nutrition is the primary factor that drives reproductive performance and profitability. Research shows that a minimum body condition score (BCS) of 5 at calving and through the breeding season should be the objective for optimum reproductive performance. Calving below a BCS 5 can drastically reduce conception rates during the next breeding season.

There are several things we can do to manage the nutrition of the herd going forward. Weaning calves as soon as possible will decrease the quantity and quality of diet necessary to sustain a cow. Testing hay for nutritional value and nitrate levels will enable us to calculate least-cost feed supplementation and ensure that the hay is safe to feed. Another factor affecting the nutritional status and requirements of the herd is internal and external parasite infestation. Parasites increase an animal's nutritional requirements because they get their share right off the top, before the nutrients are absorbed and utilized by the animal. The negative effects of parasites are magnified during the stress of drought.

In a typical cycle of infestation, internal parasite larvae are ingested as cattle graze in normal pasture situations with adequate moisture. In a drought, we usually don’t  see normal pasture conditions. Although, with adequate moisture, in the form of rainfall or even heavy dew, in late spring and early summer, internal parasites can  reproduce normally. Between then and the late summer, a drought can likely slow or stop re-infestation. However, one of the most damaging internal parasites, Ostertagia, has the ability to arrest its development and wait in the lining of the digestive tract until conditions improve. If we get fall rains and late season pasture growth, these larvae will rapidly mature into egg-laying adults and can cause severe re-infestation before frost. Some products will kill the arrested larvae, and some will only control the active populations in the animal. Discuss appropriate treatment for your specific operation with your veterinarian. Egg counts to determine infestation levels followed by strategic anthelmintic treatment may be prescribed, or de-worming the entire herd could be the most effective plan of action.

It is easier to assess external parasite problems and to know when and how to control them. The life cycle of most fly pests requires moist manure and 10 to 14 days to develop from an egg to an adult. Although drought conditions are not conducive to normal development of fly populations,  it is not uncommon to see threshold levels of infestations of 100 to 200 flies per cow. Control is imperative since flies, ticks and lice infestations can consume over a pint of blood per day and have as much negative effect on nutrient requirements as internal parasites.

The parasite situation for each operation should be evaluated so the appropriate control program can be implemented. Parasite control will enhance the nutritional status of the herd. Nutrition drives reproductive performance, and reproductive performance drives the overall profitability of your operation.

Clay Wright
Former Technical Consultation Manager