Worming - Wendover Heights Equine

Transcription

1 Worming - Wendover Heights Equine Worms are parasites; this means that they live in and off the horse for their own benefit, at the expense of their host and potentially causing damage. The horse will protect and support their growth and allow them to multiply, infecting more and more susceptible individuals. Most equine worms live in their adult form within the horse, either in their intestine or migrating around their body. They then lay eggs, which are expelled in the horse s faeces. Outside the body under certain conditions of temperature and humidity, they hatch into little larvae, which live in the pasture. Horses will ingest these without knowing when grazing. These larvae then develop into adults within the horse and the cycle starts again. What worms affect horses? 1. Small redworms (Cyathostomes) 2. Large redworms (Stongyloids) 3. Tapeworms (Anoplocephala) 4. Large roundworms (Parascaris) 5. Bots (Gasterophilus) 6. Pinworms (Oxyuris) 7. Threadworms (Strongyloids westeri) 8. Lungworms (Dictyocaulus arnfieldi) Most worms are highly specialised and do not cross species barriers. Why worm your horse? The statistics say that 80% of worms are found in 20% of horses. This means that all horses have worms but usually in low numbers that do not cause any problems. However, a few horses will suffer very high burdens that will contaminate pasture, put other horses at risk and they themselves may suffer serious ill effects, which may even be fatal. Therefore, worming your horse is going to reduce the risk of them suffering disease and reduce the risk of them causing other horses to suffer disease. Possible signs in a horse with a high worm burden; Dull coat Thin Lethargic Poor performance

2 Pot belly Diarrhoea Colic More serious complications: Small redworms once ingested, some larvae, instead of developing into the adult stage, will travel into the gut wall where they can hibernate (encyst) and lay dormant for a long time (usually through the winter but maybe for longer). If these build up in large numbers and then all burst out of the wall at the same time (usually in spring), this can cause a lot of irritation/damage. The horse may get colic, diarrhoea, possible dehydration and may even die. Most horses develop immunity to this parasite. However, young horses that have spent fewer than three seasons grazing may be more at risk. Large redworms once ingested, instead of the larvae going straight into the gut, they move through the blood vessels and into the arteries of the intestine. They remain there for about 6 months and then they travel to the gut as adults. It is in these blood vessels that they can cause severe damage, leading to blood clots, which can remove the blood supply to that piece of gut. This then dies and the horse becomes very sick with colic and will need surgery. This is potentially the most dangerous parasite. Tapeworms these live as adults in the part of the gut between the small and large intestine. They can cause irritation that may lead to spasmodic colic. They can also cause a blockage if they build up in large numbers, which can lead to a surgical colic. The irritation they cause sometimes leads to the gut telescoping in on itself (intussusceptions) and again this causes colic that needs surgery if the horse has a chance of surviving. Large roundworms these tend to cause more problems in foals and young horses as development of immunity over time is good. The eggs can live for a long time in the soil (years). Once the larvae are ingested, they move through into blood vessels and along to the lungs. Here they are coughed up and swallowed, where they are then taken to the small intestine and live here as adults. They can cause poor growth, digestive and respiratory problems. It s not advisable to graze newborn foals on pasture that has been grazed by foals the previous year. Bots bot flies land on the horse s legs and body where they lay yellow eggs that stick to the coat. Horses ingest these as they lick themselves and then they develop into bot larvae in the stomach. Eventually, they are passed out in faeces and hatch into adult flies. They may cause mild damage/ulceration to the stomach lining.

3 Pinworms the larvae are ingested; they move through into the large intestine where they develop into adults. The females will move out to the rectum, where they lay their eggs around the anus. This can cause anal irritation and excessive tail rubbing. They are one of the least harmful worms but are usually an indicator of further worm species infestation. Threadworms foals are susceptible during the first few weeks of their lives. Threadworms can cause severe diarrhoea. Undetected infections in pregnant mares are transmitted to the foal via the milk. Lungworms these commonly affect donkeys but can affect horses that are grazed with them. They cause respiratory problems and coughing. WHY ARE WORMS MORE OF A PROBLEM THESE DAYS? 1. Management The way we manage our horses is very different now to how it was even 10 years ago. They are becoming a more popular pet to have, and they are also being further domesticated from their wild roots. We re keeping our horses in larger herds, on smaller grazing areas. In other words, a lot of populations have a high stocking density. This means that horses are forced to graze closer to their droppings, hence are more likely to ingest more eggs/larvae. There are also so many different policies in place that it s easy to get confused, especially on a big yard where no one person is responsible for a single programme, meaning that despite efforts at avoiding pasture contamination and individual burdens, it s still happening. People forget that worms can be picked up from any contaminated pasture. For example if a faecal sample has been taken, that has come back clear and the livery pasture is well managed, poo-picked etc, it s assumed that the horses are safe. However, if a horse goes away for any time and grazes land at a competition for example, it may pick up a burden there and come back to contaminate the clean pasture and clean horses at home. 2. Encysted worms Mainly small red worm larvae that hide in the gut wall. undetectable and resistant. They are 3. Drug use and resistance

4 The drugs themselves can be a point of confusion, having different activities against different types of worms. More and more new wormers are being brought out every year and it is important to read the information on them. We have also been more reliant on drugs over the last 50 years and this has lead to drug resistance. Drug resistance is the ability of worms in a population to survive drug treatments that are generally effective against the same species at the same dose rate. This resistance happens in all drug groups and cross-resistance can happen between similar drug groups. In the UK, we have widespread resistance to benzimidazoles but not to pyrantel/ivermectin/moxidectin. We can delay the onset of this by using them responsibly. It occurs when the most susceptible worms are successfully eradicated, leaving behind the worms with the genes for resistance. This will result in the next generation of worms being resistant. How to test for resistant worms The most obvious sign will be a persistent parasite burden despite anthelminitic treatment. This may be detected through signs a horse is showing (thin, poor coat, pot belly, diarrhoea etc). Another way to detect it is the faecal egg count reduction test, where a faecal sample is taken before and 10 days after worming. The faecal egg count should have reduced by >90%. There are various other laboratory methods that can be used if resistance is suspected. What to do if resistance is found The same class of drug should not be used on the premises again in the short term (it is also likely to be ineffective in the longer term). Any individual leaving the premises should be monitored on any new pasture to try to prevent spread of resistant worm populations. How to avoid resistance Ensure correct dosing by measuring the horse s weight as accurately as possible. Under dosing will lead to survival of those worms that have a resistant tendency, needing a full dose to be eradicated. Remember that heart girth weigh tapes do not accurately estimate the weight of high performance horses, fit horses, unfit horses, pregnant mares and horses on a high fibre diet and certain breeds. Read the instructions on the packet for dosing intervals - do not worm more regularly than advised. Only worm if necessary - the practice of good pasture management and regular faecal egg counts (FEC)/tapeworm blood tests are recommended. Regular FEC will also enable resistance to be picked up in the earlier stages.

5 Annual rotation of anthelmintic classes - this may not be recommended where resistance to a group has been reported. It is not recommended that moxidectin be used more than once a year. HOW DO YOU KNOW IF YOUR HORSE HAS A WORM BURDEN? 1. CLINICAL SIGNS This means what signs a horse is showing eg. thin, dull coat, potbelly, diarrhoea, and intermittent colic. You may also see some worms expelled in the faeces, for example small red worms or some live pinworms at the anus of your horse, or their mucous-coated eggs. 2. FAECAL EGG COUNTS (FEC) This involves taking a fresh faecal sample and sending it off to a laboratory where they will count the number of worm eggs found in a gram of faeces. For this test, 5-10g of fresh faeces is needed. If it cannot be sent within an hour of collection, it must be stored in a fridge to prevent eggs from hatching. It will only detect eggs from small/large redworms and large roundworms, not larvae that have hatched or tapeworms or encysted larvae of small redworms. It helps to give an indication as to how many adults are living in the intestines, which will in turn give an indication as to how much pasture contamination there is. For example, if a FEC comes back with a count of 300 epg (eggs per gram), say a horse produces 4kg of manure a day, this equates to 1.2 million eggs onto the pasture! 3. BLOOD TESTS Bloods can be taken to detect levels of tapeworm burdens. Bloods can also be taken to give you an idea of the inflammatory reaction and protein loss going on in the body of a sick/colicky/poor horse that may indicate worm damage. WHAT TO DO IF YOUR HORSE IS BURDENED? If your horse is diagnosed with a significant worm burden or tapeworm burden through a faecal egg count or blood sample or is showing a lot of the clinical signs that would fit, the best thing to do is to seek some advice about using an anthelmintic drug. The best person to seek this advice from is your vet. Usually we would simply advise that you use an appropriate wormer, dosed correctly, and we would give you further management advice on how to prevent further pasture contamination and reinfection. It is also important not to forget that if you worm your horse, keep them in a stable for 48 hours after administration of the drug so that any live eggs/larvae

6 being expelled whilst the adults are dying, will not contaminate the pasture. If you are giving a 5-day course of Equine Panacur Guard to a burdened horse, it needs to remain in the stable for the 5 days also. Be careful when dosing young foals or pregnant/lactating mares as some products are not licensed for these individuals and may not be safe to use. Read the instructions carefully or contact your vet. Generally, foals start to be wormed from 4 months of age. If the mare has been wormed during the last three months of pregnancy, some immunity will be passed onto the foal naturally to cover it for the first few months of its life. Foals at risk from threadworms may need worming from 4 weeks of age. To avoid this, mares should be wormed at around the time of foaling. ANTHELMINITIC CLASSES - MACROCYCLIC LACTONES WHAT DRUGS TO USE? IVERMECTIN eg Eqvalan, Panomec, Eraquell, Noramectin The recommended dosing frequency for these is 8-10 weeks. They are highly effective against adult small redworms but do not do tapeworms. MOXIDECTIN eg Equest, Equest Pramox The recommended dosing frequency for these is 13 weeks. They are highly effective against adult small redworms and have activity against encysted larvae. Equest will not have any activity against tapeworms, but Equest Pramox does. - BENZIMIDAZOLES MEBENDAZOLE eg Telmin FENBENDAZOLE eg Panacur paste /granules/ Equine Guard The recommended dosing frequency for these is 6 weeks for the paste/granules and 6-12 months for the 5 days course of Equine Guard The single dose will kill adult small redworms and some immature stages, although there are problems with resistance. The 5-day course has activity against encysted small redworm larvae. They have no action against tapeworms.

7 - TETRAHYDROPYRIMIDINES PYRANTEL eg Strongid P, Pyratape P, Provid paste The recommended dosing frequency is 4-6 weeks. The recommended dosing frequency after a double dose for tapeworms is 6-12 months. They have good activity against adult small redworms but not the encysted larval stages. Some resistance has been found to this drug. A double dose will have efficacy against tapeworms. - PYRAZINO-ISOQUINOLINES PRAZIQUANTEL eg Equitape The recommended dosing frequency is 6-12 months. They only have activity against tapeworms. - PYRAZINO-ISOQUINOLINE + MACROCYCLIC LACTONE PRAZIQUANTEL + IVERMECTIN eg Equimax, Eqvalan Duo The recommended dosing frequency is 6-12 months. They have a high efficacy against tapeworms and adult small redworms. N.B. They will all be effective against large redworms, parascaris and oxyuris unless stated. HOW TO PREVENT WORM BURDENS? This is where it all gets a bit complicated! There are so many systems and practices that can be followed and a lot of the decisions will depend on the environment that the horse is kept in and the history of the individual and the premises. Worming control tends to be a lot more efficient if there s one person responsible for putting in place a programme that every horse sticks to. The age range of horses grazing the same fields will affect the susceptibility to having high burdens. Young horses are more likely to be heavily burdened and therefore are more likely to contaminate the pasture. Immunity is quite unpredictable but generally the rule is that older individuals are more immune. The history of parasite-related problems on a property should influence the programme, for example, a site with a lot of history will need a more vigorous programme. Any history of worm resistance on the land will also influence which wormers to use.

8 Stocking density and whether or not the land is poo-picked, rotated, mix grazed or rested should affect what programme is used. The main aims are to minimise pasture contamination and to minimise the horses parasite burden. These in turn greatly affect each other. Minimising pasture contamination could be achieved by treating all horses or just horses with a high burden. The advantage of treating all horses is that you won t miss any! Obviously, the disadvantages are that it s expensive, unnecessary and will speed up the emergence of resistant worms. The advantages of only worming those with a high burden are the reverse. The disadvantages are that those with a low count will still be contributing to pasture contamination and could develop into high burden individuals. Pasture hygiene is important in minimising eggs and larvae in the soil, as discussed later. Having a good programme in place, which everybody using the grazing sticks to, is vital in controlling worm burdens. Here are some techniques people use: 1. INTERVAL DOSING This is used if the management in place is very random or if there is regular coming and going of horses with an unknown worm history. It s basically a system whereby every horse is wormed according to the dosing intervals of the wormer used, regardless of their burden. Some people will modify it and use the wormers regularly through the higher risk summer grazing period. The disadvantage of this is that if we have a particularly mild autumn/winter, the peak period for eggs and larvae hatching may be later in the season, hence horses will still be ingesting contaminated grass when they have ceased being wormed. As discussed, it is also expensive, in a lot of cases (80%) it is unnecessary and will speed up resistance to the wormers. 2. STRATEGIC DOSING This is when horses are wormed at specific times of the year to try and disrupt the seasonal cycling of the parasites. For tapeworms this is generally in April and October and for other parasites at turnout in the spring, in the middle of the grazing season and again in the autumn. Bots can be targeted in December, when the adult flies have died off. This however does not account for abnormal weather causing an early or late peak in pasture larval burdens. It also doesn t cover for horses with very high burdens being turned out on the pasture and if mixed age grazing is practiced, whereby young horses with less significant immunity are turned out with shedding adults.

9 3. TARGETED DOSING This is arguably the best policy. Faecal egg counts are taken from all horses at intervals appropriate to worming and if they come back with no or low burdens, the horses aren t wormed. Horses with high burdens (>200 eggs per gram) are targeted for treating with anthelmintics. Generally, samples are taken every 3 months initially and if a low burden is detected each time, this can be dropped to every 6-9 months. For tapeworm, biannual testing is recommended and again if a low count is detected each time, this can be reduced to annual testing. The disadvantage is that encysted small red worm larvae cannot be detected. The advantages are that it is cheaper in the long term, more environmentally friendly and it minimises the risk of resistance to wormers developing. 4. STRATEGIC + TARGETED Strategic should help to minimise pasture contamination at critical times of the year and then targeting the high burden cases should prevent disease in these individuals and further prevent pasture contamination. It will also include worming all horses against encysted redworms at the end of the grazing season with a licensed product against these i.e. Equest or a 5 day course of Equine Panacur Guard. 5. PASTURE HYGIENE This should really be used in conjunction with all of the above programmes although sometimes it is just not convenient. The aim is to prevent/minimise pasture contamination. This means that the parasite lifecycle is never completed as horses don t come into contact with the contamination - hence adults do not hatch to produce further contamination. Stabled horses are separated from their own faeces several times a day, so they don t eat contaminated food and they also don t come into contact with food contaminated by other burdened individuals. Grazing horses however, will ALL encounter infective parasite larvae. If the land is heavily stocked or there are young horses grazing the area the infective dose will be greater. Methods for reducing pasture contamination; - REGULAR POO-PICKING the suggestion is at least twice weekly during the spring and summer and once a week during the winter. This is very effective at suppressing faecal egg counts. - MANURE HEAPS should not be accessible to grazing horses.

10 - PASTURE ROTATION this involves resting a pasture for a minimum of 3 months whilst grazing another, then rotating back. This relies on infective eggs/larvae dying before they re ingested. It s not fool proof as sometimes in mild weather, the eggs and larvae can live for longer than 3 months in the soil. Harrowing may help to bring the larvae deep in the soil to the surface where weather extremes may help to kill them (it either has to be very cold or very hot/dry (over 20 C) for this to work. - MIXED SPECIES GRAZING cattle and sheep will ingest equine eggs/ larvae but these cannot survive in these species. - DO NOT OVERSTOCK the ideal is 1 to 2 horses per acre.