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Professor RR Pascoe AM, DVSc. FRCVS. FACVS
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One of the most important benefits to emerge from the use of “worm paste” worming has been the lower occurrence of colic in the horse.
Due to the ease and convenience of worm paste treatment for internal parasites in horses, there is really no excuse for not worming all types of horses on a regular basis.
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The importance of worming to prevent colic
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Research into colic has shown that up to 80% of fatal colics can be related in some manner to the presence of parasites. This can take the form of impaction of the small intestine with the large round worm (or ascarid) and can occur in any horse aged up to 2 - 3 years old and usually is found in relation to old horse paddocks or stables, particularly where manure pickup is neglected.
The ascarid or roundworm is a prolific egg layer and has a particularly thick eggshell, which is very resistant to drying out, and can live for years in stable and yard soils. This worm is often overlooked as a potential cause of trouble, and some of the current worm pastes are not always effective against immature forms of this parasite.
It is important with worm control to discuss your worm programme with your own veterinarian, as some rotation of the type of worm treatment may be necessary, both to keep worm numbers down, and to prevent worms becoming resistant through the prolonged use of a worm paste which fails to remove all the worms.
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Types of worm pastes and drenches
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Benzimidazole worm drenches have been very effective against most worms including the larval worm of the Strongylus species, particularly the so-called ‘blood worm’ Strongylus vulgaris.
More recently the introduction of Ivermectin and Doramectin ranges of drenches and pastes have shown a very effective action against all stages of all common horse worm cycles. They also have a prolonged action and horses may require drenching only every 12 – 14 weeks.
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Life cycle of the 'blood worm'
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The larvae of the 'blood worm' Strongylus vulgaris spend a portion of their life cycle burrowing into the bowel wall, penetrating the arteries of the bowel, migrating into the larger arteries, causing damage to the artery wall, and finally migrating back into the bowel to develop into mature egg laying worms.
It is the passage through the arteries and bowel walls, and later within the large arteries, that severe damage can occur to the blood supply to portions of the intestine.
If there is complete blockage, the bowel will be severely damaged and will become necrotic and rupture, usually with severe signs of colic.
If the damage only partly blocks the blood supply, this can cause small areas of bowel damage, causing low-grade chronic pain, or it can interfere with the actual motility of the bowel wall, leading to faulty digestion, indigestion, the possibility of gut pain, and so leads to colic, rolling end may result in a twisted bowel.
So the usage of the newer, improved pastes and drenches have helped reduce this type of colic.
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Giving worm pastes
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Be careful, however, that the horse has an empty mouth when it is treated with paste, as the paste can also stick well to any food in the mouth, and when this occurs the horse can spit much of the dose out of his mouth, and so in effect is not wormed at all.
A good policy to follow is the use of pastes fairly regularly, aided by a stomach tube treatment once or twice yearly.
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Teeth problems and colic
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Horses with bad teeth that are causing pain and improper chewing, often swallow coarse, partly chewed feed, which can be another cause of indigestion. Care and regular attention to teeth overcomes the problem. Greedy eaters who gulp down their food may have to be slowed down with smaller feeds given more frequently.
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Management of feed, water and bedding to prevent colic
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Do not give large quantities of green, sappy feed, such as Lucerne or clover to horses that are either not used to it, or are over-hungry.
The same applies to water. If a horse is very thirsty, or over-heated, do not allow access to very cold water - give water that has lost the chill, and only small quantities until the horse has lost the main edge of its thirst.
Other areas that have to be watched are new bedding, particularly barley straw - some horses will eat excessive quantities and develop impaction or even spasmodic colic from over-eating.
Also remember that heated or soiled feed in the hot summer months can cause indigestion due to the toxic products produced from being over-heated and spoiled, resulting in severe cramps and violent colic, often within hours of eating.
Gas colic is often the result of feeding wilted or heated cut green feed, lush grass, access to bread, fruit, and fresh grain and also to over-eating pelleted feeds.
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Impactions
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Impactions occur from the ingestion of coarse feeds, by ground feeding and the ingestion of soil and sand.
Another cause of impaction in the horse is the present day use of synthetic fibres, plastic bags, feed bags containing synthetic fibres, baler twine and a host of other synthetic non-digestible fibres, which can be deliberately or accidentally eaten by horses.
These often lodge in the large colon and are matted with coarse feed fibres, becoming impregnated with minerals from the feed. These become capable of causing blockage and intermittent colic. Treatment is usually surgical if large and frequent doses of oil fail to correct the problem.
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Hernias can cause colic
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Other less obvious causes of colic are related to hernia of the intestine into umbilical hernia, into the scrotum of colts (inguinal hernia) and may also occur internally where small intestine can become lodged over ligaments that hold the body organs in position.
The cause of internal hernias can often be related to rolling and is one of the reasons for horses with colic to be kept moving in a bid to prevent rolling.
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Treatment of colic
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When it comes to treatment, there are many remedies that have always worked and often the reason they have worked is because the horse had a simple gut pain (colic) related more to indigestion than a serious bowel problem like those just described.
Many colics are simply indigestion and, provided the horse is relieved of gas pressure in the stomach, is given laxatives such as paraffin oil and sedatives to contain the pain, many recover fully in a short time.
However, if these measures are taken and the horse is no better, or is worse in 2-3 hours, then a complete reevaluation of its condition should be made.
Unremitting pain despite heavy sedation is always a poor sign for an uneventful recovery. Where a horse’s heart rate continues to rise, pain remains severe along with sweating, rolling etc., further tests may be necessary to allow proper evaluation of the horse’s condition.
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When is surgery necessary?
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An elevated or rising heart rate is always an indication of a worsening condition, and too much emphasis cannot be given to early prompt treatment. Surgery is not necessarily the last ditch treatment.
If, however, a positive diagnosis is reached indicating a severe bowel accident, then it must be decided very quickly whether surgery is to be done or not, as every delay markedly reduces the survival chances of the horse.
As loss of fluids into the inside of the gut is common in twisted bowels, it is often necessary to give large volumes of intravenous solutions as soon as a serious condition is confirmed.
This can mean up to 20-30 litres of fluids in the next 2-3 hours. More will probably be necessary if surgery is commenced.
Due to the high costs of surgical materials, fluids, and antibiotics for up to 7-10 days post- surgery, it is important that a full discussion of costs of such surgery be examined before becoming deeply involved in such procedures.
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Professor Reginald Pascoe AM, BVSc. MVSc. DVSc. FRCVS FACVSc is an Equine Specialist and principal of Oakey Veterinary Hospital in Queensland. His research has covered many aspects of equine related problems and he currently holds four Veterinary Association and industry awards for veterinarians in his honour. More
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