Well, it has finally warmed up.  And with three to four days of warm weather I have already started seeing flies on many of the cattle I work on daily.  So what are your options to control flies and other parasites to minimize the damage done to your cattle’s production? Let’s take a look at several options for both external and internal parasites.
Parasites, both internal and external, cost the livestock industry billions of dollars yearly in lost production.  Managing and controlling these pests is critical for long term success in livestock production. Control of internal parasitism involves the strategic use of anthelmintics, pasture management and timing.  There are multiple dewormers available for use. They come in the form of injectables, oral drenches and topical pour-ons.
Late spring in this part of the country is a great time for deworming, as the parasite burden carried by cattle is generally pretty high and deworming now can kill the greatest number of worms with a single treatment. This also helps to decrease the amount of contamination on new pastures that cows may be moved onto during the summer grazing season. I recommend concentrating on young stock as they are the most susceptible to parasite infestation. Adult cattle may benefit from systemic deworming, but work with your vet to determine your need and risk.
Producers that integrate some forms of rotational grazing can decrease parasite loads on pastures by proper management of grazing areas.  Not letting the grass get too short, rotating pastures frequently and not overstocking pastures are all tools that can reduce parasite loads and even reduce the need for deworming of adult cattle.
External parasites are the most noticeable concern during the summer months on cattle. Research has suggested that as few as 200 flies on an adult cow affect her eating habits, and in turn, her ability to maintain weight and produce milk. Again, there are several modalities for control. My favorites are pour-on insecticides and fly tags. Always follow label directions for products used, including frequency of application. Don’t expect your pour-on treatment in May to keep flies off cows until July. For convenience, fly tags offer a great option for season-long control of flies. Read the labels to learn the length of control a particular tag provides, and apply tags to maximize fly control. There are a couple of points to remember when using fly tags. First, don’t use the same tag year after year. I recommend changing chemicals every one to two years to reduce development of resistance to the insecticide.  Don’t just change brands; make sure the insecticide is an entirely different class of chemical.  Secondly, remove the tags following the fly season.  Leaving tags in until the next year increases the chance for resistance because as the fly tags lose potency, flies can become exposed to sub-lethal doses of insecticide and resistance develops faster.
Work with your veterinarian to develop plans for decreasing the impact of parasites on your cattle.  Some basic steps can improve milk production, weaning weights, reproduction and overall herd health.  
Mike Bloss, DVM, owns Countryside Animal Clinic with his wife, Kirstin Bloss, DVM, in Aurora, Mo.

AdministratorOn-Call / VetMissouri,On CallWell, it has finally warmed up.  And with three to four days of warm weather I have already started seeing flies on many of the cattle I work on daily.  So what are your options to control flies and other parasites to minimize the damage done to your cattle’s...The Ozarks' most read farm newspaper, reaching more than 58,000 readers in Missouri, Arkansas and Oklahoma