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Getting your mare ready for the breeding season

Scone Equine Hospital - Tuesday, June 30, 2020
Getting your mare ready for the breeding season

In the dark depths of winter, it is sometimes easier to think about log fires and hot cups of tea rather than getting your horses ready for the breeding season!But now is the time! If we start early, we can get a head start through management of nutrition and identifying reproductive problems before we start breeding.Nutritionist Dr Nerida Richards and Veterinary Reproduction Specialist Dr Jen Clulow discuss how to maximise reproductive efficiency in your Mare and Stallion, so they are ready for peak performance when the time comes!

Feeding the dry mare

Our aim for the dry, non-pregnant mare is to be ready for the breeding season in good, but ‘light’ body condition which is increasing as she enters the breeding season.What we often don’t recognise is that being overweight for a horse carries just as many health problems as it does for humans. In overweight horses we see increased levels of:

  • Insulin resistance
  • Laminitis
  • Increased bone and joint wear and tear
  • Lack of mobility; and
  • Heat stress


All of these problems can also contribute to poor reproductive performance!Reduced mobility can result in poor uterine clearance mechanisms and mares with equine metabolic syndrome may also have an increased susceptibility to uterine infections as well as abnormal cyclicity.

Feed plenty of forage

Forage (hay, chaff and pasture) provides your mare with many of the calories they will need to maintain weight during winter. Aside from that, forage will keep your horse warm in winter. During the digestion of forages in the horse’s gut, bacteria ferment the fibrous portions. One of the ‘by-products’ of this fermentation is heat, and it is this heat that really helps a horse to stay warm during winter.Because of the ‘warming’ properties of forage, your mare will benefit more from an additional feed of hay than an extra feed of grain, pellets or sweetfeed in very wet, cold weather.

Adjust your horse’s diet to control body weight

Because you will be condition scoring your mare regularly you will know if your horse is maintaining, gaining or losing weight. Depending on what you want your mare to be doing, you may need to adjust the diet to keep her at the bodyweight and condition you want.If your mare is gaining unwanted weight, you will need to reduce or remove high energy feeds like grains, pellets, sweetfeeds or oils in the diet. If your mare is losing weight that you don’t want her to lose, you may need to feed more calories in the diet. You can do this by:

1. Feeding more hay and if you’re not already doing so feeding some lucerne hay.

2. Adding high energy feeds to the diet like pellets, sweetfeeds, oil or high energy fibres like lupin hulls, copra meal or sugarbeet pulp. Use the best quality feeds you can afford and if using a sweetfeed look for one that contains either extruded or micronised grains as these are more digestible for horses.

Feed a balanced diet

An unbalanced diet doesn’t meet your mare’s requirement for one or all of energy, protein, vitamins and minerals. Meaning your mare will experience deficiency and won’t be as healthy as she could or should be. Nutrient deficiencies can lead to:

  • Weight loss
  • Delayed cyclicity
  • Suppressed immune system
  • Muscle wastage
  • Increased susceptibility to diseases like greasy heal and respiratory disease
  • Dull, dry coat and skin
  • Brittle and slow growing hooves

While traditionally, knowing if what you were feeding was meeting your horse’s requirements was quite hard, using a service like the FeedXL Nutrition Calculator makes it very easy to see if what you are feeding is the right thing for your horse.

And finally…

Of course all the normal rules of good horse husbandry apply in winter. The start of the breeding season is a great time to get an overall health check, a dental exam, spring faecal egg count and de-worming where necessary and make sure she is up to date with her vaccinations.

Getting the dry mare ready for the breeding season

Once we have her nutritional requirements taken care of, we can focus on making sure she is breeding fit!Breeding early in the season can be beneficial for several reasons, especially if you encounter a problem along the way.But how can I get my mare cycling early?

Light therapy

The mare is a long day breeder.This means as the daylength starts to increase, the mare will start cycling.Putting mares under lights will help to advance the breeding season by artificially increasing the daylength.Advancing the breeding season in your mare not only helps to produce early foals but more importantly, allows additional time for breeding management should you encounter any problems.Light therapy can be achieved by putting the mare under lights or the placement of an Equilume™ mask on the 1st July 2020.A minimum of 60 days of 16 hours light therapy is required to advance vernal transition or “spring heat” in the mare.This preparation should have your mare cycling normally in September.

Early breeding

Vernal transition or “spring heat” is the first cycle of the season.The cycle requires some priming with oestrogen to get going properly and the effects can be extreme with mares teasing to the stallion for weeks on end.The first cycle of the season can be quite unpredictable as teasing mares may have follicles which grow and regress without ovulating.Because of the unpredictability of this cycle, many breeders may elect to breed on the second, more predictable cycle of the season.The mare’s oestrous cycle is 21 days in length.Therefore, if you see your mare teasing to a gelding or the stallion every week or every fortnight, chances are that she is still transitioning to a normal breeding cycle.Hopefully with the nutritional aspect taken care of, her transition should be relatively smooth and we can get on to breeding her!

Ironing out some problems – The pre breeding evaluation

The main benefit for getting the mare ready early is so that problems can be identified and rectified before breeding her. Ask yourself, why is the mare dry?Did she just wean a foal?If that is the case and you elected to not breed her last season, then that’s great!A quick pre breeding examination by your veterinarian should be able to identify whether she is cycling normally (not transitioning) and there are no abnormalities noted.Pre breeding cultures of the uterus and the clitoris may be required by some studs prior to breeding.These cultures need to be taken when the mare is in season (in oestrus) and may help to identify any problems your mare has before you take her to the stallion or order semen for artificial insemination.Identifying abnormalities at the start of the season may save you a lot of money and heart ache later in the season.If your mare is dry because she failed to achieve a pregnancy last season, this pre breeding check is a must!Identifying and addressing these problems may be the difference between a live foal and an empty mare.

Breeding options

Live Cover

Breeds such as Thoroughbreds are restricted to a live cover situation.Usually mares are managed intensively and are sent to the stallion when they are ready for a single breed.The advantages of live cover include per cycle pregnancy rates of 60-70% and low maintenance mare preparation.However, mares need to be in standing oestrus, meaning she must be receptive to the stallion. Consequently, this breeding strategy has the potential to injure both the mare and stallion.It is also very important that all humans are safe during the procedure!

Artificial Insemination: Cooled sperm

Cooled semen is available throughout Australia.Disadvantages of cooled semen include unreliable courier services, intensively managed mare preparation and not all stallions are suitable or available for cooled semen insemination.Advantages of cooled semen are that you can expect per cycle pregnancy rates similar to that of live cover (60-70%) provided your mare is managed correctly.Stallion spermatozoa can be cooled for up to 48 hours with adequate fertility.Ideally cooled sperm is inseminated within 24 hours of collection and the mare ovulates within 12 hours of insemination.This requires some intensive management on your veterinarian’s end, occasionally with some long-range forecasts required to get the semen at the insemination centre at the right time.It is important to understand how cooled semen is shipped around Australia and the costs involved before using this method.If you are in a remote location, frozen semen insemination may be a more reliable method if your mare is a suitable candidate.

Artificial Insemination: Frozen Sperm

The use of frozen spermatozoa opens a number of genetic possibilities for breeders here in Australia.Spermatozoa can be sourced from local stallions with a busy competition career, deceased stallions and stallions living abroad.It is important to ensure that your mare is a suitable candidate for frozen breeding as results can be disappointing.Internationally, pregnancy rates with frozen spermatozoa range between 30-70% with an average of around 50% per cycle conception rates with good quality frozen spermatozoa.Unfortunately, there are no international standards for frozen spermatozoa so different numbers of spermatozoa and different numbers of straws make up a “dose” and post thaw motility rates can be highly variable.Frozen spermatozoa are also often sold as “doses” or “straws” rather than “pregnancies” so make sure you read your breeding contract carefully.Foal heat is usually avoided, and aged mares are often not suitable candidates for various reasons.

Written by Dr. Jen Clulow