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I’m no historian, but rumour has it that the origins of St. Valentine’s day are quite unromantic. Valentine was a Roman guy who helped Christian couples to get married. This was frowned upon in Rome at the time so the Emperor, Claudius Gothicus, had Valentine stoned and beheaded. Anyway, I thought I’d continue this soft, gooey theme and offer you some nuggets of information about the romantic lives of domestic animals. Brace yourselves.....

Once again, the UK has been hit by an outbreak of infectious disease - but this time it’s horses that are affected. As a result, the headlines are full of “Horse Flu!!!” stories, racecourses are closed, and some people are recommending horse owners have their horses vaccinations “topped up” to minimise the risk. So what’s going on? How severe is the risk? And what can we do to minimise it?

Winter is well and truly here and scraping the frost off my windscreen the other morning reminded me of a common question from my clients at this time of the year; that is whether or not frosty grass is more likely to cause laminitis. There are many misconceptions about laminitis, the commonest being that lush pasture is the primary cause. The reality is that this is incorrect and I have seen many cases occur in horses and ponies grazing barer paddocks, both in summer and winter. In fact, studies have shown there’s an approximately four times higher risk of laminitis in both the summer (June–August) and winter (December–February) months compared to the lusher growth months of spring (March–May).

Endoparasites;  the gut-wrenching villains that terrorise our horses from their tums to their bums, but how big an issue are they for the average horse? Which worms do we need to be aware of? Is wormer resistance really that big an issue? So many questions, so many drug names.

What is a worm?

A worm, or an endoparasite, is an organism that lives inside of your horse, to your horse's detriment. We have all seen the adverts for ‘good bacteria'; this is known as a synergistic relationship, where both host and occupier benefit. With parasites, only the parasite gains.

1. Cyathostomes. Why did the cyathostome always get what he wanted? Because he was so encystant… Excuse my awful jokes; it’s been a long day. Cyathostomes are a type of nematode, or round worm, known as small encysted redworm.  The adults, when in the large intestine, produce eggs that the horse will excrete onto their pastures; the eggs then hatch, and the larvae are eaten by the horse. It is also the larvae that are capable of encysting (hiding) in the walls of the large intestine. So the saying really is true, don't eat where you… These nasty critters can encyst in the mucosal lining of the large intestine of horses; the larvae are capable of ‘hypobiosis’; they stay in a state of arrested development (a bit like hibernation).  It is when they emerge that they can cause potentially fatal damage and diarrhoea, known as larval cyathostomosis.
2. Strongyles (large redworms). These nematodes are detrimental to your horse in a different way than their smaller namesakes. Eggs in the pasture have a moult phase, referred to as Larval stage 1, L1, and moult to form, logically, L2. The L3 are consumed by an unwitting grazer; it is the L4 stage that migrate from the gut to the arterial supply of the intestine (the cranial mesenteric artery if you are curious). This can cause a compromised blood supply to the large intestine with inflammation of the arteries known as verminous arteritis, and can cause the dreaded colic.
3. Parascaris Equorum (ascarids); another nematode. Are you the owner of a young horse? This one is for you (sorry!).  Thankfully, our equid amigos develop a resistance to these worms; however, young-stock in the 6 month – 2-year old bracket are highly susceptible. The eggs are passed out in excrement, and moult to L1 and then L2; unlike large redworms, it is the second larval stage that is ingested. They, too, have a damaging migratory pathway; from the intestines, they migrate through the liver and moult to L3, before progressing to the lungs.  From here, they can be coughed up, swallowed, and moult to L4 and then adulthood in the small intestine before starting the whole cycle again. Liver and lungs may be damaged, but impacted colic from a heavy worm burden, along with ill-thrift and a pot-belly, are common signs.
4. Dictyocaulus arnfieldi (lungworm) is another nematode. To my horror, it is donkeys that are particularly affected by lungworm, and carry it, as the life cycle is not actually completed in the horse.  These larvae are ingested, and burrow out of the intestinal wall into the bloodstream, where they penetrate the lungs. They will cause reactive changes in the respiratory system, such as coughing, increased mucus production and irritation of the bronchi. Chronic pneumonia, secondary infections and pulmonary oedema (fluid on the lungs) may be other features in heavy burdens.
5. Anoplocephala (tapeworms); a cestode, not a nematode. It requires an intermediate host to develop to a larva from an egg, and it finds a host in the oribatid (harvest) mite. When the horse eats the mite with the parasite, the adult tapeworms can then settle in the caecum (the huge fermentation chamber of the horse gut) and small intestine. Tapeworms pose a real threat to your horse by associations with spasmodic colic; it can cause food impaction and intussusception, when the colon ‘telescopes’, folding in on itself. Inception may be about a dream within a dream, so think of intussusception as a colon within a colon.

Other parasites include Oxyurius equi (pinworms, causing itching and irritation around the anus) and Gasterophilus (bots; actually a fly larva, and not known to cause many problems despite settling in the stomach).

What can we do about worms?

I have been on many yards with rigid worming routines as a means of prevention as much as treatment: this is called interval dosing. Is it necessary? If I had to fall in a strict ‘yes’ or ‘no’ camp, I would be in the latter. Wormers, known as "anthelmintics", are becoming less efficacious; that is to say, anthelminthic resistance is becoming a real problem. The more that worms are exposed to wormers, the more the wormer becomes a selection pressure; some worms will have innate features which allow them to survive despite these chemicals specifically designed to kill them – pesky mutants. The more that we use wormers when we may not need to, the stronger this selection pressure is; we kill the worms which are susceptible to the wormers, allowing the few worms which can survive to reproduce in an environment with less competition. Thus, new wormers need to be developed all the time; a laborious and long task. How can we slow or stop this resistance developing? By being responsible owners and avoiding ‘over-worming’ - saving our horses and wallets in the process! Moving away from wormers, we need to look to management. As we can see in the life-cycles, it is the output of eggs in faeces that are responsible for providing a suitable environment for parasites. Poo-picking fields is one of our biggest weapons in the battle of the bugs; deploy it often! Quarantining new horses prior to turn-out can help to minimise worms on a busy yard; moxidectin and praziquantel can be used 24 hours prior to turn-out. What wormers are available? There are macrocyclic lactones (ivermectin and moxidectin), tetrahydropyrimidines (pyrantel) and benzimidazoles (fenbendazoles) and pyrazinoisoquinolines (praziquantel). We must treat with what is most efficacious for the type of worm, and also only when it is needed. Faecal egg counts (FECs) give a picture of what worm eggs are being put out in your horse’s faeces; when the FEC exceeds 200 eggs per gram, it may be justification for worming. If that sounds a lot, we need to get our heads around the fact that horses will always have worms; whilst this is not a pleasant idea, unfortunately our horses will never have a totally worm-free body, and we shouldn’t strive for that in our worming regimes. Further to this, we want to keep a certain worm population ‘in refugia’; this means we want to keep some worms unexposed to wormers, because then we are not selecting for worms resistant to the wormers. It is only when worm burdens get too high and will damage our horses’ well-beings that we should use wormers. FECs can reduce the selection pressure that help those resistant worms to thrive, as well as being a cost-effective means of targeting the individual horses who need it most.

Is there an ideal worming regime?

Perhaps not. FECs will not give an accurate representation of encysted populations, and are not deemed specific enough for tapeworm counts. Fecal egg flotation or ELISA (enzyme-linked immunosorbent assay) blood tests can be used for tapeworms, but are more expensive. Furthermore, an ELISA detects the antigen (the immune response to a parasite) level, thus the burden may appear high as antibodies are still circulating against the old burden, even if the worms are now dead. However, there are means of interval dosing that do not require administration of a wormer, regardless of whether the horse needs it. We must focus on what burdens are of concern and when… SPRING: Performing a faecal egg count (FEC) for strongyles; ivermectin or single dose pyrantel can be utilised if there are over 200 eggs per gram. Stronglyes were previously a huge concern for causing colic, but thanks to ivermectin, they have become less of a menace, hence the need to protect the efficacy of this wormer by responsible use. Additionally, treatment for tapeworms in the form of praziquantel or double dose pyrantel may be used in spring. SUMMER: FEC for Strongyles and treatment when the FEC indicates, again with ivermectin or pyrantel. AUTUMN: we must treat for any encysted cyathostomes. Remember the larval cyathostomosis? Commonly these larvae will encyst, and emergence can occur in late winter/early spring. Treatment of a heavy burden is advisable; a five day course of fenbendazole, or a single dose of moxidectin are licensed for encysted cyathostomes. However, a large amount of dead worms and a huge inflammatory reaction can spell out a disaster in the form of colic, so if there's a heavy burden your vet may recommend using the older (and less potent) but "gentler" course of fenbendazole first, and then following up with moxidectin 4-6 weeks later to "mop up" any survivors. Tapeworms can be treated with praziquantel or double dose pyrantel again at this time of year. WINTER: The same treatment (or not!) for strongyles when indicated; if bot flies were a problem over the summer, ivermectin or moxidectin will kill the larvae in the stomach. From all of us here from VetHelpDirect, we hope your horses have a wonderfully worm-free year ahead! There is nothing so good for the inside of a man as the outside of a horse. ~John Lubbock

While the sun's glorious rays may leave us jumping for joy, and our saddles, we must be vigilant about ensuring our horses' well-being. Here are some top tips to avoid the dreaded heat stroke, and ensure our four-legged friends have as much fun in the sun as we do! What is heat stroke? Heat exhaustion is characterised by: 1. An elevated body temperature (hyperthermia; a temperature exceeding 41oC/105 F); 2. An elevated heart rate (tachycardia; the normal heart rate of a horse is 36 – 42 beats per minute, although this may be higher in smaller ponies) 3. An elevated respiratory rate (tachypnoea – exceeding the normal 8 – 12 breaths per minute); 4. A tired, unresponsive horse; 5. The horse's gums will feel dry and tacky; if you press on them, the area under pressure will turn white, and the time to return to normal colour will be longer than in a non-thermally stressed horse. Vets may describe this as a capillary refill time in excess of 3 seconds. If there is no intervention, the condition may escalate to heat stroke where the horse may stagger, appear depressed or, in extreme cases with central nervous system damage, collapse and have convulsions. This is a serious medical emergency that we have the ability to prevent. [caption id="attachment_4392" align="aligncenter" width="350"] Keep them cool![/caption] So how do I keep my horse cool in summer? 1. Water, water, everywhere! Often, people believe the old wives' tale that they should not allow a hot horse to drink water; however water is essential to maintain adequate hydration status. Horses sweat to lose excess body heat; the heat of their body then evaporates this water, leaving their skin colder. Excessive sweating without enough water to drink leads to dehydration, which can be very dangerous, causing a drop in blood pressure and an increased heart rate. Thus cool, clean water must be provided at all times, especially in outdoor grazers, to ensure they can replenish their hydration states. 2. Elect to keep your horse cool. When horses sweat, they lose essential salts from their body, known as electrolytes. Notably, horses lose proportionally more potassium in sweat than other mammals. Offering water with added electrolytes or a salt lick may be advisable. Salt stimulates thirst receptors in the horse's brain, so may have an added effect of encouraging them to drink. If providing electrolyte-infused water, ensure that there is ample fresh water available, as some horses dislike the taste (have you ever had Dioralyte? I can't say I blame them!). 3. Shady characters Horses in the wild and our domesticated critters will seek shade when turned out. Natural shade such as trees can be a great advantage. Bear in mind that the position of the sun changes throughout the day; ensure that your horse has protection from all angles of the sun, whatever the time. 4. Cool runnings Anyone who has been running in the searing midday heat has experienced the unpleasant (and in my case, unattractive) phenomenon of being sweaty, red-faced and exhausted. Horses' huge muscles will generate enormous amounts of heat. Try to time your rides for cooler times of the day, such as early mornings or evenings. If you are lucky enough to have access to beaches or woodlands, these cooler areas can be ideal for summer strolls. 5. Lose a coat like it's going out of fashion! Horses wear their beautiful coats all year round, but generally have a much lighter summer coat. However, some ponies, for example native breeds, will naturally have a heavier summer coat. Additionally, horses and ponies suffering from Cushing's syndrome may have hirsutism – failure to shed their winter coat. In such cases, clipping may be advisable, to ensure they are not excessively insulated. 6. Mystical creatures Misting your horse with cool water will help your horse to lose heat from the skin by evaporative cooling. 7. Splash about For many horses, a tepid bath can be most enjoyable. Be sure to use a sweat-scraper to remove excess water. If you choose to wash post-exercise, walking your horse gently in a cooler will prevent a sudden drop in temperature and aid in an effective cool down. 8. Ice queen Adding ice to water can be refreshing for your horse, though excessively cold water may put him off drinking it. Ice packs are frequently applied to horses' legs after intensive exercise, and there is no reason why this should not continue to be practiced throughout summer. 9. Be your horse's biggest fan American-barn style stables often have excellent ventilation. If it is safe (i.e. without trip, electrical or fire risks), using a fan in a stable with no air flow can help to keep your horse comfortable. 10. Always wear sunscreen Baz Luhrmann may not have been targetting horse-owners, but the 1999 hit rings true; animals with pale areas of skin are particularly susceptible to sun-burn. Think especially of cremellos, pink noses, white socks, pink sheaths and pink anuses – areas under the tail are more susceptible than you may think when your horse deploys his best fly-swatter while grazing in summer! Some owners elect to use specific horse suncreams which are available, and some will use high SPF human suncreams. Whichever you decide, be sure to ensure that your horse is not allergic to any of the ingredients before applying liberally. All of us here at VetDirect wish you and your horses a very happy, healthy summer! “Horses make a landscape look beautiful” - Alice Walker. Rachael McKinney