Worm Control in horses

Transcription

1 Horse Internal parasites There are a number of worms that infest horses; the most important are the large red worms (also known as large strongyles), the small red worms (also known as small strongyles), threadworms, tapeworms, pinworms and large roundworms (ascarids). The large strongyle Strongylus vulgaris has larval stages which migrate in the mesenteric arteries of the gut. Such migrating worm larvae damage blood supply to the horse s intestines and directly cause potentially fatal colic attacks. The most common worm species seen in regularly wormed horses these days are the small strongyles and ascarids. Large strongyles are not as prevalent any more, due to the widespread use of mectin pastes & drenches. Tapeworms may cause intestinal blockages and thereby colic if horses have heavy burdens. Large and small red worms (strongyles) and the other intestinal worm species produce eggs which are passed in the manure. These eggs hatch and develop within the manure into immature worms which are known as infective larvae. Due to the variety of conditions under which horses are used and housed, horse owners should develop a worm control program for their own situation in consultation with their veterinarian. Worm control program An effective worm control program consists of most or a selection of the following : drenching to remove worms from the horse; limiting reinfestation by removing manure, harrowing paddocks, using grazing management practices; and monitoring worm burdens using worm tests. Drenching A drench is a chemical or mixture of chemicals that is capable of killing the worms inside the horse s body without harming the horse. There are many different drenches on the market today.

2 The three main chemical groups are benzimidazoles (white drench), morantel or pyrantel (clear drench) and macrocyclic lactones. It is recommended that chemical groups be rotated as required to target particular worm species and thereby delay a build-up of resistance in worms to a particular drench chemical. Drench program Foals Foals should be drenched from 6 weeks of age and drenched every 6-8 weeks, until 12 months of age as this is the high risk time for acquiring ascarid infestations from contaminated pasture. Pregnant mares Pregnant mares should be treated just before foaling to control Strongyloides westeri (intestinal threadworm) which are passed from mares to foals in the milk. Healthy adult mares are not generally infected with roundworms (ascarids). Make sure the drench is safe to use in pregnant mares. Generally in pregnant mares, drenching may be required as often as every 6 to 8 weeks in confined paddock situations, or less frequently when reinfestation is being controlled by other means. Other horses Drenching may be required as often as every 6 to 8 weeks, or as little as twice a year, depending on the drench used and whether reinfestation is being controlled. Use a worm test to determine when drenching is necessary and to monitor for any development of resistant worms. Administration of Wormers Paste and gel drenches Pastes and gels are convenient and easy to use. Dosage is easy to adjust. Always ensure the horse s mouth is empty of food, and deposit the drench as far back in the mouth as possible so the horse doesn t spit it out. Powder and liquid drenches Some powder and liquid drenches are sufficiently palatable to be accepted when mixed with feed, particularly if molasses is used to disguise them. Liquid drenches are preferably administered into the mouth using a drenching syringe. Frequent loss of drench is a problem with oral administration of liquid drenches. Care needs to be taken to avoid underdosing which leads to the development of resistant worms.

3 Granules and pellets Drenches available as granules and pellets have been specifically formulated for mixing in the feed. Usual recommendations are to give a smaller than normal feed and to dose each horse separately. Molasses is useful in disguising drench taste. Stomach Tube drenching Stomach tubing is done by a veterinarian. The drench is delivered directly into the horse s stomach, so dosage is accurate and there are no problems with large volumes or unpleasant drench odour or taste. A wider variety and/or mixture of chemicals can be used. Dosage Correct wormer dosage is essential. Never under-dose. If you don t have access to large animal scales, consider floating your horse to the local weighbridge. Alternatively a girth weigh tape may be used. Limiting worm reinfestation The number of worm eggs or infective larvae on the pasture or in the horse s environment can be physically reduced by several management practices. Remove manure regularly from stables, yards and paddocks daily or every 3 days. Harrow the paddock and spell it during hot, dry conditions for 6 to 8 weeks. Alternate grazing of horse paddocks with another species such as cattle or sheep. Wash perineum and udder of pregnant mares before foaling to limit foal exposure. Clean and disinfect foaling boxes and stables. Avoid feeding horses on the ground; use feed bins and hay nets or racks. Foals and young horses should be given priority for low-worm pasture as they are most susceptible to significant disease from worms. If possible, segregate horses by age. Do not put mares and foals on paddocks previously grazed by weanlings or yearlings as these paddocks are likely to be highrisk for worms. WORM TESTING PROGRAMS Worm tests measure the number of worm eggs in a manure sample and can be used to estimate the worm burden in the horse. A worm test can also tell you what species of worms are present in your horse.

4 Regular worm tests can provide an indication of the effectiveness of your worm control program. They can be used as a guide to when drenching is necessary and they can be used to assess the result of a treatment and any worm resistance. Worm test results should be interpreted along with such factors as the age of the horse, any clinical signs of worm infestation, seasonal conditions, intended pasture use of horse paddock, stocking rate of horse paddock, and management practices. A horse worm test kit detects the presence of egg-laying adult worms in the horse. It cannot detect larvae and immature stages of worms, which can cause significant disease. For this reason you should consult your veterinarian for an interpretation of worm test results. Rotation of wormer compound used helps reduce the development of worm resistance to that particular group of the wormer compounds. Chemical groups should be rotated as required to target particular worm species and thereby delay a build-up of resistant worm populations. Horse worm tests provide a valuable guide on the effectiveness of the current drench program, on any worm resistance on the property, and on the effectiveness of your paddock and other management practices to reduce worm populations. Wormer compounds and some Commercial products (in italics) There are 3 main groups of horse wormer compounds. Benzimidazoles Oxazole, Equinox - wormer compound is Oxfendazole Panacur 100 wormer compound is Fenbendazole Pyrantel or Morantel Equiban wormer compound is Morantel Macrocyclic Lactones Noromectin, Equimec, Imax LV wormer compound is Ivermectin Eraquell Pellets - wormer compound is Ivermectin Promectin, Valumec wormer compound is Abamectin Equest wormer compound is Moxidectin Macrocyclic Lactone - With Praziquantel (for tapeworms) Imax Gold, Genesis Equine, Equimec Plus Tape, Juramectin Plus wormer compounds are Ivermectin + Praziquantel Equimax, Promectin Plus wormer compounds are Abamectin + Praziquantel

5 Equest Plus Tape wormer compounds are Moxidectin + Praziquantel Combination Wormer Products. These can provide some control against the development of resistant worms within some species of worms. However, other worm control strategies are needed to counter this problem, along with a worm test program. Strategy T : wormer compounds are Oxfendazole & Pyrantel Ammo, Moramectin Solution wormer compounds are Abamectin + Morantel Equimax Elevation wormer compounds are Ivermectin + Pyrantel + Praziquantel Equitak Excel wormer compounds are Abamectin + Oxfendazole + Praziquantel Equimec Triple Liquid - wormer compounds are Ivermectin + Oxibendazole + Praziquantel Contact : John Cronin, Veterinarian PO Box 18137, Clifford Gardens Toowoomba Qld 4350 Mobile: Phone: Fax: john.cronin@nfw.com.au