Grazing operations take advantage of year-round pasture, but farmers must still deal with manure and the flies that come with it. Good grazing and manure management practices in late winter and early spring grazing can help stave off potential fly issues and create more resilient pastures.

It’s important to understand the lifecycles of the worst pests for grazing livestock, including the ubiquitous house fly. In addition to being major pests of livestock, house flies serve as vectors for disease and can transmit pathogenic bacteria that are resistant to antibiotics.

Dr. Sandra Swiger, assistant professor of veterinary entomology, Kansas State, explained that adult house flies are driven by their need for food. Female house flies are especially motivated to seek food since they require sugar and protein for egg production.

“Flies are attracted to manure, animal feed and secretions around the animals’ eyes and nose,” said Swiger. “That’s where we run into issues with flies going to manure, then back to secretions and possibly transmitting disease. One of the main ways to reduce flies is to reduce access to their preferred food source, which reduces the ability to produce eggs.”

Pesticides are the traditional management tool for fly control, but it’s difficult to administer pesticides on pastured animals, and easy to forget flies in colder months. To compound the problem, house flies have become resistant to many chemical products. Proper winter and early spring grazing management can help with the resistance problem.

Swiger explained how resistance develops: “We treat a cow that has flies on it and the flies are not yet resistant to the chemistry of the product. If we use the same products too close together or without rotating, the flies are overexposed to the same chemistry. They didn’t die the first time, so they’re exposed to the same chemistry again and again. Where there might be five flies that should die when exposed to the treatment, one fly doesn’t die because it has developed resistance. That surviving fly lays 100 or more eggs, and the population increases.”

When one fly passes forward the traits that made it resistant, there are now an overabundance of pesticide-resistant flies. Swiger noted the importance of paying attention to product label ingredients and becoming familiar with chemicals because products with different names often contain the same ingredients.

Combatting insecticide resistance begins with an IPM program for fly management, which includes management of winter hay debris and manure. “Good sanitation includes changing habitat to eliminate breeding sites,” said Swiger. “Remove resources and eliminate areas where flies lay eggs and larvae grow … such as manure, decomposing substrate or feed.”

Horse flies are also a problem and can be vectors of mastitis among cattle. Only female horse flies bite to obtain blood for egg production, and typically bite just once a week so it’s difficult to manage them with chemical products. Horse flies lay eggs on stones and around water.

Deer flies prefer wet substrate such as spring mud. It’s difficult to find deer fly larvae, and since they are highly predacious and will devour other deer fly larvae, there may be only one or two in some areas.

Manure, flies & early season grazing

Beef cattle wintered on a good sacrifice pasture won’t cause excessive pugging and compaction. Photo by Sally Colby

Most pastured livestock operations confine animals until pastures are dry in spring. While most producers have a general timeframe regarding animals returning to regular grazing, the move to pasture is usually a matter of watching and waiting.

Keep records of where cattle are and when and how bales are fed. Take pictures of various livestock housing areas, including sacrifice areas, to help plan next year’s winter feeding strategy.

Supplemental winter hay feeding can influence fly development. If hay is fed in a stationary ring or cradle, cattle are drawn to one area and deposit manure and urine there. For better nutrient distribution, move hay rings regularly or feed from a moveable wagon to help distribute nutrients. Avoid feeding hay in heavy traffic areas, near gates or around mineral stations.

Other options for winter hay feeding include bale grazing or rolling out hay bales. The ideal situation is to feed winter hay on a concrete feeding pad in a well-drained area, then scraping manure from the pad and storing it until weather conditions allow for spreading.

In some cases, limit-feeding hay is a more economical choice that usually results in less waste and less manure production. Cattle that receive supplemental concentrate in winter will have higher nutrient output, so allow for those levels.

A sacrifice area can vary in size, depending on land resources. Cattle kept in a barnyard with shelter usually have limited space, and manure is collected for composting or spreading when appropriate. If cattle spend winter on a sacrifice area, late winter and early spring grazing management involves decisions about when cattle will return to regular grazing.

After moving cattle from a sacrifice area to pastures, keep an eye on the sacrifice area and check for weeds, poor drainage and other issues. If weed growth is excessive, manage the weeds as soon as possible to prepare the area for reuse.

Excessive mud can be managed temporarily with a load of wood chips, but that isn’t a long-term solution. Careful observation through the season can help with planning better drainage for the following year. Poor drainage should be addressed when the ground is dry.

Mud is a given for late winter and early spring. The mix of mud and manure in a poorly-drained sacrifice area is the perfect breeding area for certain flies. The occasional warm days of early spring bring early flies, which can reproduce rapidly, so watch for fly development where manure/mud muck has accumulated.

Before animals are turned out to regular grazing areas, keep an eye on the paddocks not in use to determine where cattle will graze first. Those paddocks should be well-drained to allow for heavy spring rain and located close enough to the sacrifice area to allow easy movement of cattle if those areas become too wet. Early spring cattle grazing on wet pastures can result in pugging and compaction.

Spring is also the time for livestock housing clean out. Make sure your manure management plan complies with state regulations regarding land application. Many states prohibit manure application when the ground is frozen or snow-covered.

The interaction among flies, manure and grazing animals is complex but can be managed with careful planning, observation and willingness to adapt throughout the seasons.

by Sally Colby