There are three groups of internal parasites which can damage the gut and cause disease in the horse in Guernsey. The information below will hopefully explain the importance of developing a sound worming regime, using the best products at the correct time.
Roundworms come in many different forms but to simplify the situation, in the adult, Guernsey field grazed horse, the group known as cyathostomes (red worms) are the principal problem. They are grazed on the pasture as microscopical larvae which bury their way through the intestines and over many months migrate around certain organs of the body and the arteries of the intestines, depending on the worm type. They then return to the wall of the intestine where they live for a while (encysted) before bursting out into the gut to form adult worms which produce eggs causing further contamination of your pasture. Donkeys suffer from an additional worm called lungworm.
The horse tapeworm, Anoplocephala is found at the ileocaecal junction (near where your appendix is sited) of the horse and can cause major disease such as repeated colic. Tapeworms have an interesting life cycle which cannot be completed without an ‘intermediate host’. In the case of Anoplocephala, this is the harvest mite found on the pasture during the summer and autumn and to a lesser degree in hay. The horse eats the mite; the tapeworm is liberated in an immature form and over many weeks changes to an adult tapeworm.
The Bot fly, Gastrophilus, is the fast moving, bee like fly which buzzes around stables and fields in the summer months. Eggs are laid by the fly on the horse which ingests them while grooming itself. The eggs hatch by this process, the larvae bury their way through the back of the tongue and all the way down to the stomach, where they erupt and form masses of large grubs which cling to the stomach wall. There is still debate on how serious a disease risk they are but some forms of digestive upset and colic are blamed on them. The adult flies can make horses bolt.
There are many different horse worming products on the market. All products have worm resistance and therefore are not 100% effective.
Control of worms in horses is still an essential requirement to maintain equine health. Only 20% of the horse population carry a significant worm burden. Therefore 80% of horses do not need regular worming. Nowadays horses should receive ‘strategic worming’; that is they are wormed based on their worm burden and on the time of year rather than worming to a set programme. Any new horse introduced to a yard should be wormed with Equest Pramox or with Panacur Equine Guard followed by Equitpae and kept in a box or restricted paddock for a couple of days with collection and disposal of droppings prior to any introduction to communally grazed pasture. This particularly applies to horses brought in from outside the Island.
Worm egg counts can be carried out at Isabelle Vets on a small quantity of fresh faeces tested within 24 hours of collection. The worm burden within an individual horse can be quantified and either we can advise you on treatment or when to carry out the next worm egg count. The production of eggs is minimal over the winter months and therefore we would recommend worm egg counts from the middle of March through to October. A worm control programme ideally involves all horses on a yard.
Tapeworm is transmitted within a mite that can be found in grass, hay or haylage it is impossible to avoid. Tapeworm infection cannot be diagnosed using faeces but can be monitored by blood sample or a saliva test. Alternatively, a specific tapeworm treatment (Equitape) can be given every six months.
We advise the following worming protocol:
Remember to either keep the horse in for 24 hours after worming or to make sure that ALL droppings are picked up ASAP. No worm product kills 100% of worms, hence the necessity to follow the above protocol.
Your worm control will only be as good as your management. Picking up droppings in the field daily, not allowing the ground to go ‘horse-sour’ and keeping noxious weeds at bay are essential. Rotating cattle or sheep after the horses have grazed will help prevent worm infestation on the pasture.
Targeted worming prevents unnecessary use of anthelmintic drugs. This will, in turn, reduce the amount of medication used and that which passes through the horse’s intestine to land on the pasture. Both of these processes can contribute to drug resistance. Currently, there are no new worming treatments on the market and therefore we must use the drugs we have responsibly. It is accepted that horses can carry a low level of worms to provide some stimulation of the lining of the gut which in turn improves the horse’s defence to disease. It is proposed that overuse of certain wormers may contribute to susceptibility to diseases such as grass sickness.
Therefore the message is: use the right drug at the right dose in the right horse at the right time!