Choosing To Breed

Making the decision to breed from your mare should not be taken lightly. There are many unwanted and neglected horses that could have been avoided if people did not breed carelessly and without thought. Therefore I consider the primary question you should be asking yourself now is:
“Why are you breeding from your mare?”

Are you choosing to breed because your mare is a much loved pony that your family has now outgrown? If this is the case will the potential foal actually be suitable for your purpose or in fact be too small? Putting a big stallion to a small mare will not guarantee an offspring half way in-between - like humans they may take after the father or the mother. Before you breed because of sentimental reasons, ask yourself is your mare of good enough type or does she have faults that you are choosing not to see?

A common explanation I hear is that people are putting a mare in foal because she is too sharp or difficult in temperament to be ridden, which is a terrible reason to decide to breed. Temperament is certainly hereditary and a horse with a difficult nature is likely to pass this onto the foal, and even at a professional level, horses need to have both ability and a trainable disposition.

Breeding because of injury to the mare also needs to be considered carefully, as potentially the weakness or a predisposition to the injury may be directly hereditary or the conformational attributes that predisposed the injury may be inherited. If you have any concerns regarding this point you should discuss the situation with your own vet before proceeding.
Breeding to sell or breeding to keep? Sadly the notion that you can make lots of money breeding horses seems to rarely eventuate especially if you do not have your own property. The potential cost of breeding a single foal for you to keep is likely to far exceed the cost of buying one already grown. You need to consider firstly the cost of putting your mare in foal including veterinary fees and stud fees. Then you should add the potential livery costs for the mare while she is in foal, then with the foal at foot and once the foal is weaned. Where are you going to foal the mare down and how much will that cost? When do you plan to sell the progeny, as a foal, yearling or once they are being ridden and consequently what will the cost be of keeping them until that point? Will you insure the foal and what will the costs be for vaccinations, passport, microchipping, castration and other unexpected injuries or illnesses?

If you are planning on selling the offspring what is the realistic amount you are likely to get for them and how does this compare with the actual cost of producing a horse from birth to the point of sale? Even using the best of bloodlines for both the sire and dam does not guarantee a potential superstar and high value off-spring.

That said, there is nothing quite like the satisfaction of competing on a horse you have watched come into the world and produced through the grades yourself. In addition, not all horses have to be professional athletes and breeding from a sentimentally valuable mare to produce a pleasure horse that will be loved and have a happy home for life cannot be considered a bad thing to do. So if after considering the question "why are you breeding from your mare?", you are still keen to proceed then it is time to contact your stud veterinarian to discuss your individual situation.

Worms & Worming

Red Worms


There are numerous types of gastrointestinal parasites or “worms” as they are more frequently referred as. Worms are a burden on the horse’s gastrointestinal tract (GIT). This burden can range from being completely sub-clinical (the horse shows no ill effects from the infestation) to reducing a horse’s performance in events, causing colic, diarrhoea, weight loss and in severe cases horses can die as a result of parasitic infestation.

The most common and pathogenic worms that infest horses are, cyathostomins (small worms or small redworms), large strongyles (large red worms) and tapeworms. Large red worms were historically a problem but are now far less prevalent and cause less clinical disease. Small red worms are very common affecting all ages but mainly young horses (1-4 years old). Most infections are subclinical.

The small red worm life cycle: the larvae are eaten by the horse off the pasture and move through the GIT. They then burrow into the gut wall and can stay there for weeks, months or even years. They stay there until conditions are just right then they emerge from the gut wall and mature into adults where the adults produce eggs that are shed in the faeces. The eggs in the faeces then develop on the pasture into the larvae that are eaten and so the cycle continues.

The larvae in the gut wall are called “encysted” and these are very difficult to treat. Only two drugs can target these encysted larvae: a 5 day course of Fenbendazole or Moxidectin. If a large number of worms erupt from the gut wall at the same time then horses can develop severe problems. Encysted larvae don't produce eggs and so it is important to remember that a horse can have a low faecal egg count (FEC) but still have a high worm burden.

The tapeworm life cycle is different as they don't burrow into the wall but they shed their eggs intermittently so a negative WEC does not mean no tapeworms. A high tapeworm burden can cause colic. A blood test is available to detect antibodies against tapeworms, but this only gives an indication that they have been exposed at some point in the last 6 months.

Wormers Red Worms  Tapeworm
  Adults  Encysted Larvae Annual/6 month dose
1 d Fenbendazole     √    χ     χ
5 d Fendendazole     √    √        χ


  √    χ


double dose

Ivermectin       √    χ    χ


   √     χ
Praziquantel     χ    χ     √


Anthelmintic “wormers” have different effects and so target different worms at different stages of their life cycle. This table shows which worms are killed by the different active ingredients in wormers.

80% of worms produced in a field come from 20% of the horses. This means that the majority of horses on a pasture have few worms and so produce only a very small number of eggs. These horses are ‘low egg shedders’ and they do not need worming as they won’t be suffering adverse effects of having worms and won’t be significantly contributing to pasture contamination. The small group of horses that make up the 20% will be ‘high egg shedders’. These horses will have a FEC>200 eggs per gram. For an unknown reason these horses will be persistent egg shedders despite the same or similar pasture management as their herd mates. It is these horses we need to target with wormers to reduce pasture contamination and infectivity.

Each time you worm your horse a small number of the worms present will be resistant or “immune” to the effects of the wormers you use and so will survive worming. If you repeatedly give the same type of wormer to all horses on the pasture, over time the number of resistant worms in your horses' GIT will increase until all the worms are resistant and your wormer will no longer work. The oldest wormers (Fenbendazoles) have the highest resistance and the newest wormers have the least resistance (Moxidectin). It is important to understand that there are no new wormers being generated. Donkeys are already resistant to Moxidectin.

If you are worried about resistance developing on your yard then your vet can perform a faecal egg count reduction test (FECRT). This test measures the efficacy of the wormer you have used.

To reduce the development of resistance we can do four things:

1. Allow a population of sensitive worms “refugia” to survive the worming process. These refugee worms will dilute and compete with the resistant worms for resources. This competition will stop the development of an entirely resistant population. To do this we have to use a targeted worming protocol.

2. Reduce the use of wormers by only worming those horses with a FEC above 200 epg.

3. Manage the environment to minimise our reliance of wormers. We can do this by reducing the number of horses per acre, regular poo picking (everyone’s favourite summer pastime), mixed grazing with sheep and cattle and finally harrowing fields on hot dry days so the sun destroys the eggs in the soil.

4. Quarantine new horses so they don't bring resistant worms onto the yard. New horses should also be wormed for tapeworm and encysted larvae before being turned out.

Worming Programmes:

Firstly, no one protocol will work for every yard and if you have any concerns please consult your vet about your specific yard requirements so we can tailor a programme for you.

Regular worming - worming every 4-6 weeks will reduce disease BUT will lead to resistance and a shift in the type of worms you will see, so this is NOT a sustainable management protocol. Worming at specific times of the year can be successful in disrupting the worms' life cycle, however, changes in weather pattern or the introduction of heavily contaminated individuals will reduce your success and won’t help heavily burdened horses.

Targeted worming - treating each horse as an individual is the BEST strategy. You must use a FEC to select those horses who are shedding >200 epg and only worm those horses, the “high egg shedders”. By doing this you will reduce pasture contamination and reduce the development of resistance. It is also a CHEAPER worming protocol. You must have a FEC from every horse because 80% of the worms are produced by 20% of the horses so in a herd of 30 horses only 6 will be significantly shedding eggs but you won’t know which six unless you sample all 30.

We recommend that as part of any worming strategy, tapeworm should be targeted twice a year in autumn and spring, and that encysted worms are targeted in winter.

Chris Baldwin, BVetMed, MRCVS


All horses, ponies and donkeys should be vaccinated against tetanus, a condition that equine species are very susceptible to. Sadly, most cases die, very few live and a huge amount of time, money and effort is required to keep them alive if they do survive. Vaccination against tetanus is very effective.

Tetanus is caused by a bacteria called Clostridium tetani that lives in the soil, the horse's digestive tract and the environment. This bug likes to propagate itself in places that do not have much oxygen, an anaerobic bacteria. Usually horses become infected after a puncture type wound becomes contaminated with the Clostridium bug, a deep wound is an ideal oxygen free site for the bacteria to multiply. Other types of injury that can lead to problems with tetanus would include puncture wounds to the foot and wounds within the mouth.

It is important to keep a close eye on wounds that are quite small externally that may have punctured deeper into the tissues than first thought. It is particularly important to check horses out in the field with thick coats or wearing rugs in winter.

The spores from the Clostridium bacteria produce a series of neurotoxins that are circulated around the body in the blood stream and enter the central nervous system. The main neurotoxin is neurospasmic and it is these neurotoxins that cause the problem and the clinical picture that we see with horses with tetanus. The neurotoxins cause a spasm of muscles, without really any twitching. This is a tetanic type of contraction, hence the name “tetanus”.

The classic symptoms of tetanus are initially a stiff legged gait and almost a saw-horse type stance, the ears will be very erect and immobile, flared nostrils, the third eye lids may protrude, the jaw will not open, hence the old name of “Lock Jaw”, and the tail will often be held straight out behind the patient. The affected individual may be hypersensitive to noise, with its muscles going into spasm at a loud sound. As the disease progresses the patient ends up lying down and eventually the respiratory muscles become paralysed which results in death.

The signs of tetanus can occur 7-21 days after the penetrating wound. Death usually follows within 7-10 days.

Foals are particularly susceptible to tetanus, the navel is a site at which contamination with the Clostridium bug can occur. This is why it is important to have a foaling box that is as clean and hygienic as possible prior to foaling, the navel should quickly be treated with a topical antibiotic spray and a tetanus antitoxin should be given within the first 24 hours of life. Mares around the time of foaling may also be injured internally and may become affected by tetanus. Simply vaccinating the mare a month prior to foaling will boost her own antibodies and will also boost the level of antibodies within the colostrum that the foal should receive from its mother in the first 12 to 24 hours of life.

If a wound is detected on a horse it is always important to clean it thoroughly, even clip any long hair away from the edges so that the nature of the wound can be investigated properly. A cold hose is a good way of rinsing contamination out of wounds. Hoof wounds can be lavaged with a hydrogen peroxide solution. If there is any doubt about the character of a wound and the vaccination status of the patient, then veterinary attention should be sought.

If a horse, pony or donkey is thought to have tetanus, treatment can be attempted - the wound in question would be surgically debrided, opened up to allow oxygen in and lavaged to remove contamination. A tetanus antitoxin can be administered in massive doses to neutralise the neurotoxins and antibiotics such as penicillin will be used to kill the bacteria. Other than this it is a case of nursing the patient in a cool, dark, quiet space; usually intravenous fluids are given to maintain hydration status. Sedatives and muscle relaxants can be used to control the muscle spasm. Often the bladder and rectum do not work properly so it may be necessary to catheterise the bladder so it can be emptied and also to empty the rectum manually. Some patients may survive, but sadly very few.

Vaccination is a very effective way of preventing tetanus. Ideally the first vaccine for tetanus should be given to foals at about 3 months of age, when the antibodies that the foal has acquired from its mother in the colostrum have diminished. However, mostly foals are first vaccinated for tetanus in combination with influenza vaccine at about 7 months of age, when the maternal antibodies for flu have gone. A second vaccine is then given approximately a month later (21-92 days later in combination with the second flu vaccine). Once a horse has had 2 vaccines it should really be adequately protected within 2 or 3 weeks of the second vaccine.

Vaccination is then usually repeated with the third flu vaccine of the course within the period 150 to 215 days after the second vaccine of the primary course. The vaccine can then be repeated at the first annual booster for flu (within 365 days of the third vaccine), thereafter vaccination is only necessary for tetanus every 2 years. The exception to this is mares that are in foal and these are usually vaccinated every year prior to foaling for both flu and tetanus.

Any horse (including foals) that has not had a correct course of tetanus vaccine should be given a dose of tetanus antitoxin if a wound or foot abscess is identified.

Dr Ed Lyall, BVetMed, CertEM (StudMed), MRCVS