Morganville Mobile Vet

The Ups and Downs of Horse Breeding

WORDS BY Dr John Chopin

BVSc, PhD, FANZCVS, Registered Specialist in Equine Reproduction

(First published August 2017)

 Author Bio: John is a graduate of the University of Queensland, and finished with a PhD in equine frozen semen and ovulating agents. His extensive experience in large-scale breeding operations includes working with Australia’s first commercially used clone stallion. John has consulted to numerous practices and companies, runs continuing education to veterinarians and has published over 60 articles, including book chapters in leading texts in equine reproduction. John continues to have an interest in clinical research.

breeding your own horses

is an option many horse owners aim to try at some stage. Most owners have a mare that they want to breed from. However, very few owners decide to manage and educate a stallion with the prospect of using him as a sire. This article answers many frequently asked questions that relate to both the mare owner and the future stallion owner.

Stallions might be considered a breeding option to increase genetic gain, financial gain or prestige. Stallions are 50% of the genetic equation and, as such, are an important factor. This article answers some of the questions associated with using stallions for breeding.

What is the difference between artificial insemination and natural cover, and why should each be used for breeding?

Stallions can be used for live cover (i.e. natural mating) or can have their semen collected for artificial breeding. This artificial breeding can be for fresh, chilled or frozen semen artificial insemination (AI). The amount of processing varies, but generally increases from fresh AI to frozen AI.

Fresh AI is for relatively immediate use. Chilled AI is for transporting semen for up to 48 hours. Frozen semen is to preserve semen indefinitely and allow transport (especially internationally) or long-term storage.

There are several reasons why stallions are not used for live cover. These vary depending on the wishes of the owner. There might be breed society restrictions on the use of artificial breeding. For example, the Thoroughbred industry does not allow any form of artificial breeding, and so, if genetics are to be imported then importing the stallion is one way to achieve this. There are a lot of ‘shuttle stallions’ that travel from one hemisphere to the other enjoying a very long breeding season!

Fresh AI can be used when the stallion has too many mares to cover that day, or it is more convenient for the stallion owner to collect once and inseminate several mares. Fresh AI is useful when the mare is not cooperative even though she looks to be at the correct stage of behavioural oestrus. An uncooperative mare may be anxious, frightened or even aggressive if they are not managed correctly. An uncooperative mare can be a danger to the stallion, people and herself. A decision made by the stallion or the mare owner to collect the stallion and use fresh AI in the mare often saves much heartache in these situations.

Chilled AI allows semen to be transported from the stallion to the mare in a 24- to 48-hour period. This might occur where the mare owner cannot or will not transport the mare to the stallion and wants the option of having their mare inseminated at a facility of their choice. Also, stallion owners who are not in a position to handle mares might opt to drive the stallion to a facility to have semen collected, assessed, processed and transported to the mare. This works well for stallions in a performance career for several reasons. The stallion owner can concentrate on their stallion’s performance in training or competition. The stallion then only associates breeding behaviour with the breeding or collecting facility, minimising unwanted behaviours.

Frozen AI, or the collection of semen for frozen storage, is done for multiple reasons. This allows long-term storage of semen. Some owners use this as an insurance policy, ensuring semen is stored in case the stallion is no longer able to breed. Some owners look to export semen and frozen storage is the most convenient method but requires semen to be collected in an approved facility with quarantine and health testing performed. Some semen is collected and stored in speculation. For example, a young colt might show some promise, so the owner will store some frozen semen and then have the colt castrated.

How is a stallion collected?

The most common way to collect semen is to have the stallion mount either a mare or a dummy and direct his penis into an artificial vagina. The semen is collected from the artificial vagina, assessed, processed and inseminated.

There are other ways to collect semen. Some horses can be trained to collect on the ground. This can be used for an older stallion that might have hind limb pain that prevents him from mounting. Alternatively, chemically induced ejaculation can be used in select cases.

How many people does it take to collect a stallion?

With a very well-trained stallion and experienced personnel, it is possible to have one person handling and collecting the stallion. This, however, is the exception and it is much safer to have a dedicated stallion handler, a dedicated mare handler and then the person collecting the semen – making it a total of three people.

Is there an optimum reproductive age for stallions?

Stallions all mature at different rates and different ages. There can also be some breed differences. Most stallions start puberty between 1-2 years of age, depending on when they are born. Final maturation is usually around four years of age. It is possible to reduce a stallion’s fertility by over-use of a young stallion or with the use of some drugs. It is essential to carefully manage a young stallion that is breeding to ensure no damage is done to his fertility.

Does the stallion need to be sound?

Soundness generally refers to the horse not being lame. A mature stallion with a large breeding commitment needs to be fit and strong for the season. Any soreness can become a problem with the stallion potentially refusing to mount, due to pain. Also, the quality and amount of semen can be less with a horse that is in pain.

The next point about soundness is an ethical dilemma. The physical appearance of a horse (conformation) is important in determining whether there are likely to be problems with soundness. The physical appearance is also passed on to the offspring, and so, offspring can inherit the physical appearance of their parents – and some of the problems that may go with that physical appearance.

How is a mare inseminated?

There are several methods to inseminate a mare. The general principles are cleanliness and no trauma. With a large volume of semen, the method is to use an insemination pipette to place the semen into the body of the uterus.

With smaller semen doses, the ideal is to place the semen further up the uterus, closer to the ovary. This might be achieved with different pipettes that are capable of bending around corners and might require manipulation via rectum, with or without sedation. With very low doses, it is possible to place semen at the very tip of the uterus. This can be done with an endoscope.

What are the pros and cons of these methods of insemination?

Large volume insemination is relatively easy and cheap. The more involved inseminations with low semen doses can be more involved and expensive, as they might require drugs and equipment to achieve insemination.

How long does semen last in the various types of storage?

Fresh semen should be used in a few hours. Chilled semen can last 24-72 hours, depending on the stallion and the way it is processed. Generally, it should be used within 24 hours. Frozen semen can last indefinitely, if it is looked after properly by a professional facility.

How do you ascertain if a stallion’s semen is viable and decent quality?

This can be very important for a number of reasons. If you are considering purchasing a stallion as a breeding prospect, then evaluating the fertility of the horse is very important. Also, if you want to have an idea of how many mares can be booked into a stallion for the season, then an evaluation is important.

If you are considering using chilled semen, there are a number of different extenders and processing methods. Having a test run of different methods will work out which one is the best and, that way, a quality product can be delivered to the mare owner. It is possible a stallion’s semen might not chill or freeze well. This is important to know before offering that stallion for those services.

How do you assess the quality of a stallion’s semen?

Semen is assessed by visual characteristics, volume, concentration and motility. Some of these can be done by eye; the rest need a microscope and associated slides. It is also possible to use computer-aided sperm analysis (CASA). Although CASA is not essential, it does allow some degree of objectivity and repeatability – all important for producing good, consistent results.

Do stallions need to stay at a reproduction facility?

Not necessarily. Some clients prefer to bring them in for collections when they are required. Other clients prefer to leave stallions at a collection facility. The first option reduces costs associated with agistment but puts a burden on the owners to make the stallion available on request. The second option removes the need for the owner to drop everything and run the stallion to the reproduction facility, but the workload needs to be considered, so the agistment bill does not exceed income from services.

When is the best time of the year to collect and freeze semen?

Stallions can be collected any time of the year to freeze semen. Our preference is usually to do this at quieter times of the year. The process of freezing semen is more time involved and, in a busy reproduction centre out of season there is generally more time.

Also, some of the horses who have frozen semen collected need to be trained to do so. It is nicer to work with a naïve stallion when everything is quiet and there is no time pressure that can occur during the breeding season. If semen is being collected and frozen for export, then the facilities and animals have to meet strict quarantine standards. The necessary quarantine isolation of the stallion might be easier to achieve without the heavy traffic flow that occurs during the breeding season.

What factors reduce the performance of a stallion and the quality of their semen?

The main factors that affect quality are age, pain and the use of drugs that impair fertility. A very young horse might not have good quality semen until he reaches maturity. From 14 years of age, semen quality deteriorates, but this is very individual. Some older stallions have very good semen quality, while others deteriorate at a relatively young age. The use of drugs and supplements in performance is a common cause.

Some of these will affect fertility, especially in a maturing individual. If you are unsure of the effect of a drug on a stallion’s potential fertility, consult your veterinarian for advice.

If mare owners choose to breed, how do they start and where do they find a suitable stallion?

Stallion selection can be very difficult and depends on the desired end product. Having a working knowledge of popular or performing stallions in your discipline and their bloodlines will help you make an informed decision. There will always be someone nearby who will have an opinion – and separating the wheat from the chaff can be difficult.

Once the stallion has been selected, budget is a consideration and research into the entire costing of breeding, including service fee, agistment and veterinary fees, is important. These will vary depending on the type of breeding that is done.

Research into fertility results with your selected stallion might be difficult to obtain, but some stallion owners are very open about what they think their stallion fertility results are.

Having your mare examined by a veterinarian is also important. Ideally, this should be done before or early in the season, so the veterinarian can identify any obvious problems and possibly correct them before too much time is lost.

Is there any post-breeding veterinary care that mare owners need to consider?

Most mares have uneventful pregnancies and births. If there is a history of problems with your mare, then discussion with your veterinarian can help come up with a management plan for pregnancy. Overall, keeping these mares in good to fat condition (not obese) produces the best foal possible with very little problems during pregnancy and birthing.










Stallions at Stud



WORDS BY Dr John ChopinBVSc, MANZCVS (Equine Medicine), PhD, FANZCVS, Registered Specialist in Equine Reproduction

Author Bio: John is a graduate of the University of Queensland, and finished with a PhD in equine frozen semen and ovulating agents. His extensive experience in large-scale breeding operations includes working with Australia’s first commercially used clone stallion. John has consulted to numerous practices and companies, runs continuing education to veterinarians and has published over 60 articles, including book chapters in leading texts in equine reproduction. John continues to have an interest in clinical research.


When horses are bred to be ‘genetic superstars’ but fail to live up to their owners’ and trainers’ expectations, the questions that often arise are:





The reality, however, is that it might be too late for your equine superstar… As reproduction specialist Dr John Chopin explains, the single most limiting factor affecting a horse’s athletic potential might be the 11 months spent in utero.

An individual who is not living up to genetic expectation might already have had setbacks before they were born. These setbacks will rule their entire life and they will never live up to genetic expectation, despite all the care, supplements and training they receive.

These setbacks can be a result of changes to metabolism that are locked-in for life and the structural make-up of bones, muscles, lungs and the heart. They are all dictated and laid down during pregnancy.

There is good scientific evidence that events during pregnancy can be influenced to change the metabolism and structure of individuals as they develop.


This article will help explain why this might be the case, so future individuals may have their full genetic potential realised following birth.

Nutrition drives reproduction. Good nutrition makes mares cycle earlier in the season and more regularly, increasing the chance of going in-foal.

Low-protein diets or low-energy diets result in a higher embryonic loss rate in mares. If a pregnant mare is restricted from eating, she immediately prepares to abort with the hormones of labour increasing in her blood stream. This is an important consideration with any pregnant mare who is not eating, due to illness, or is having food withheld for a medical or surgical procedure.

A developing pregnancy changes from an embryo to a foetus when all the rudimentary organs have formed. Although the term foetal nutrition will be used in this article, embryonic nutrition is also critical.

foetal nutrition

Foetal nutrition is the balance between molecules the foetus needs to grow (oxygen, sugars, proteins, electrolytes) and also removal of harmful waste products (carbon dioxide and other waste products of metabolism).

The delivery and removal of these products occurs through communication between maternal and foetal bloodflow. This occurs at the border between the uterus (maternal bloodflow) and foetal membranes (foetal bloodflow). The combination of these two powerful units is called the placenta.

Foetal nutrition is not only dependent on what is delivered or removed, but also on how much. Changes in bloodflow from either the maternal or foetal side can change foetal nutrition. This means the dietary intake of the mare is not the only factor involved. Her overall health is important as well.

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Is she feeling well?

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Is she in good condition?

If she has a period of illness or is exposed to toxins from the environment, these might influence foetal nutrition.

One last consideration is the older mare who may have damage and scarring to their uterus. This might change the bloodflow to the placenta and also influence foetal nutrition.

There are a wide range of factors that can influence foetal nutrition. Some of these are temporary and can be treated (mare illness); others are permanent and might not be able to be accommodated (uterine damage or scarring). If the pregnant mare undergoes any change in her state of wellbeing, consideration should always be given to supporting the other individual inside her.

metabolic pre-programming

In the hours to days after fertilisation, metabolic pre-programming occurs.

Metabolic pre-programming is where the young embryo reads information about the external environment from signals supplied from the mother and adapts their metabolism to optimise their chances of survival. These metabolic decisions are locked-in for life.

There are thought to be two types of metabolism: thrifty and non-thrifty.

Thrifty metabolism: Results when the embryo decides life outside of the uterus looks tough and makes major changes to their metabolism in order to increase survival after birth.

The classic description of a thrifty metabolism is a couch potato that would rather watch sport than participate in it.

In humans, these people are insulin resistant (prone to diabetes), have altered exercise behaviour (will be sedentary to conserve resources), have altered feeding patterns (will prefer and select energy-dense foods), have reduced skeletal muscle mass (less exercise), central fat deposition (saving energy for a rainy day) and also have other alterations in autonomic control (one being high blood pressure). In humans, this can be as a result of low oxygen, low nutrition or low protein during early pregnancy.

Non-thrift metabolism: The opposite of this metabolism is the non-thrifty individual that is very active, eats whatever they want and doesn’t seem to be overweight.

These individuals developed where there was no indication to the young embryo there was a need to spare resources because environmental resources appeared to be in plentiful supply while in the womb.

size, strength, scope

SSS, or Size, Strength, Scope, are characteristics most Thoroughbred farm managers evaluate when a foal is born. This gives them feedback to give to the mare owner, so a decision can be made on who to mate that mare back to. If SSS was favourable, the mare owner might send the mare back to the same stallion. If unfavourable, the mare owner might change stallions.

Size and strength is determined by genetics, so evaluating this is incredibly important. However, other factors are involved, which might confound the decision about ideal genetic matching.

Maiden mares (a mare that has not had any previous foals) will have smaller foals than mares that have had foals before.

Maiden mares should, therefore, have their foals compared to foals from other maiden mares. This is because there is a change in the placental unit between the first and subsequent pregnancies.

The first pregnancy is almost like a priming run to optimise the function of the placenta and, from the second pregnancy, the placenta then works at full capacity. As the mare has subsequent foals, the uterus can become damaged and the placenta begins to deteriorate, and suboptimal foals can be produced towards the end of a broodmare’s career.

Bones and muscles are not the only structures that can have their development influenced by events in gestation. If there is an interruption in foetal nutrition, any organ that is developing at that time can have its structure and function impaired. If the interruption is severe enough and long enough, intra uterine growth retardation (runting), or foetal death and abortion might be the result.

Fertility of the offspring is one of the potential systems that can be damaged. Under-nutrition of sheep in early pregnancy reduces ovarian function of the female offspring.

Under-nutirition of pregnant guinea pigs in the first trimester can result in a 30% reduction in muscle fibres in the offspring. Over-nutrition of pigs during the stage of foetal muscle development can increase muscle mass.

When the foetus is in the pregnant uterus, it is important it has enough space to move and stretch its limbs. This is determined by the amount of fluid that is in the uterus.

Acute dietary restriction in mid-pregnancy reduced the size of the lungs of newborn lambs. This was a result of a reduction in fluid, due to the dietary restriction of the pregnant ewe. The reduced fluid restricted the volume the lamb had to move in. The lamb had to curl up, which caused the abdominal contents to put pressure on the diaphragm, which reduced the chest space and the smaller lungs developed in a smaller chest space.

There was a recent report on foals born with contracted limbs, which showed there were reductions in the circumference of the foetal membranes. This might have reduced the volume these foals were in and they were not able to periodically stretch out their limbs, and so, might have led to the foals developing flexural contractions.

Neurology - coordination and the ability to learn

Coordination, strength and the ability to learn need a neurological system that is working at full capacity.

The development of the nervous system is also influenced by foetal nutrition. Subclinical cobalt deficiency in early pregnancy can produce lambs that are slow to stand and suck. This made them prone to colostrum deficiency and infection following birth.

Human babies that are affected by Sudden Infant Death Syndrome (SIDS) have a reduction in their diaphragm muscles and a reduction in their lung capacity, but they also have reductions in their brain, and the nerves that drive the diaphragm and respiration.

Disease risk

There are a number of diseases present during growth and as an adult that are related to intra uterine growth retardation (or runting).

On top of skeletal muscle development and impaired athletic performance, the list includes hyperlipaemia – a fatty blood disease affecting multiple organs, including the liver – allergic conditions, chronic obstructive pulmonary disease (COPD) – the horse equivalent of asthma – and osteochondrosis, a bone developmental problem which can lead to deformities, bone cysts, joint chips and arthritis as the horse ages.


In the mare, the presence of adequate to excess body condition during cyclicity, pregnancy and lactation does not appear to have any detrimental effects. In comparison, poor body condition has measurable detrimental effects on reproduction and the foetus.

Inadequate nutrition during equine pregnancy can limit the development of foetal organs and alter metabolism permanently. In the equine, the single most limiting factor affecting athletic potential might be the 11 months spent in utero.


Risks of uterine growth retardation

Risks of uterine growth retardation

If there is an interruption in foetal nutrition, any organ that is developing at that time can have its structure and function impaired. If the interruption is severe enough and long enough, intra uterine growth retardation (runting), or foetal death and abortion might be the result.

There are a number of diseases present during growth and as an adult that are related to intra uterine growth retardation (or runting).

As well as sub-optimal skeletal muscle development and impaired athletic performance, the list includes:

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Hyperlipaemia, a fatty blood disease affecting multiple organs including the liver;

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Allergic conditions;

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Chronic obstructive pulmonary disease (COPD), the horse equivalent of asthma; and

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Osteochondrosis, a bone developmental problem that can lead to deformities, bone cysts, joint chips and arthritis.



The Trivers and Willard hypothesis: Can maternal nutrition influence the sex of the offspring?

The answer is yes, but it is more profound for litter species. Mice on high-fat, low-carbohydrate diets produce male biased litters. When mice are fed the reverse, they produce female biased litter. There is some evidence this might occur with species that produce one offspring, especially in some species of deer.

The hypothesis Trivers and Willard proposed was, if a female is looking at perpetuating her genetic line, she has to make a decision whether to produce a female or a male. In a social structure that has a harem as the predominant social and reproductive unit, female offspring will very likely breed and continue the genetic line, but with a low rate of return. A male has less chance of breeding, but if he does, the reward is a very large return for genetic investment.

So, if environmental conditions are tough and the mother is likely to produce a stunted, poorly competitive individual, then producing a female could be the best option. If conditions are ideal and the offspring is likely to be

vigorous and strong, then the mother might put all of her genetic ‘eggs’ into producing a male.