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Feeding For Breeding – Broodmares & Stallions

As with most things in life, it is easier to start the season with a horse in good condition, and maintain this, than to play catch up altering condition scores. Stallions should approach the breeding season with a condition score of 3-3.5. Scrotal fat deposits impair temperature regulation of the testes, reducing sperm counts and motility. Obesity reduces libido. Yet a lean stallion will not have the reserve necessary for the hard physiological demand of covering – sometimes up to three times a day – and the stress and anxiety any stallion feels through a breeding season will cause an energy drain. Mares, too, should start out with a CS of 3.5. Scores of less than 3 and more than 3.5 have been shown to lead to reduced conception rates and increased embryonic loss. Yet the most fertile mare is the one who’s body ‘believes’ that times are getting better, so coming out of the winter on a score of 3 and aiming to increase this to 3.5 prior to conception is ideal.

Zinc, for instance, is essential for the motility and viability of stallions’ sperm. Remember that the production of sperm starts 60 days before it is ready for ejaculation, so a good semen sample reflects a considerable period of adequate nutrition. Omega 3 fatty acids have a role in sperm mobility and sperm count.


Mares do not respond to the “flushing” system prior to breeding that is used in farm animals (beginning with a thin mare and then providing an increased nutritional plane). Ovarian activity is linked to body condition, thin mares are much less likely to be cycling normally, they also have a reduced conception rate and a higher rate of early embryonic loss. Overweight is probably just as bad as underweight. From both ends of the spectrum it makes sense to achieve target weight before attempting breeding rather than correcting afterwards.

When breaking down the diet at conception time, the micronutrients must be considered. Trace elements are vital, and these are the factor most variable in grass – especially at the end of a winter. It is known that manganese deficiencies cause re-absorption of an embryo in other species and may well in mares. Mares that do not have access to pasture at breeding time will benefit from supplementation with vitamin A and beta carotenes (Equistro do a good range of fertility supplements) Oxidative damage is a problem for all tissue, but fragile single celled entities (sperm, ova) will feel this the most, so antioxidants such as vitamin E are essential. This is easily available from grass, but poorly stored in preserved grass (hay, haylage). Omega-3-fatty acids are necessary for the production of sterols (sex hormones) and so are closely involved in a mare’s ability to hold on to a pregnancy. They also promote faster growing follicles and may also inhibit prostaglandin synthesis, allowing an embryo to become properly established. For all these reasons, the build up to the breeding season, and conception times, carry the need for formulated diets, despite the assumption that it will be later on the mare needs help.

Throughout pregnancy, two factors are important to consider; firstly, the health and future health, of the foetus; secondly, the state of the mare to provide for efficient re-breeding post foaling. The foal’s demands can be broken down into two time periods. For the first 2/3 of pregnancy, differentiation of tissues is occurring, where micronutrient availability is paramount. For the last 1/3 of pregnancy, differentiation is largely over, and rapid growth occurs. Early on in pregnancy, owners frequently feel they need to feed more. This is not true, but they need to feed better. The mare needs protein and micronutrients, yet to increase these may often give her too much energy. She quickly becomes fat – this can reduce her chance of holding a pregnancy, and stubbornly refuse to be shed later on, causing, for example, birthing difficulties. The pelvic canal is a frequent place for mares to lay down fat. Balancers can be very useful at this time – many feed companies make them, with formulated trace element content, higher protein levels, yet no need to give the mare cereals.

In later pregnancy (the last 3 months) foetal growth accelerates and around 60% of its birthweight is gained during this time.  Energy, protein, calcium and phosphorous are all needed in greater quantities, yet the growing uterus takes up space in the mare’s abdomen and reduces her appetite. In most cases, reliance on forage alone is poor practice because the mare cannot possibly ingest enough food to maintain her own condition and that of the foetus. The foetus and placenta together can require up to 7g of calcium a day in this period and 4g of phosphorous. Mares supplemented with copper in the second and third trimesters have been shown to produce foals with less physitis and less problems with cartilage at 150days.  Adequate selenium availability in the second and third trimesters is also known to reduce the incidence of cartilage erosions in the foal during its first year of life. It is recommended that (if the mare is in good condition to start) balancers are given alongside forage for the first 6 months of pregnancy and from then on a gradually increasing level of concentrate should be fed. In the last 90 days, some 25-35% of the total daily intake should be in concentrate form. For example, in the last month of pregnancy a thoroughbred mare weighing 550-600kg should be fed 3.5kg of concentrate a day with an lib forage (pasture or hay/ haylage). It should be emphasised at this stage that commercial feeds specifically formulated for breeding stock are needed; micronutrient and protein levels in “stud” mixes differ significantly from a standard “working” mix, for example.

Following foaling, the energy demand on the mare is huge and the appetite rapidly increases in marked contrast to the reduced eating capacity in late pregnancy. She produces 3% of her body weight per day in milk for 3 months – that is 18 litres in a big halfbred mare. And, often we’re trying to get them swiftly back into foal. During this first month a foal doubles its birth weight. Oil is a very useful provider of energy at this time, and is often overlooked. Certain oils have different omega-3 and omega-6 ratios, and hemp oil in particular is known to have one of the best ratios of its fatty acids, showing in humans the greatest medical benefits. This oil can be doubly useful, optimising the chances of re-conception. Continual assessment of condition of mare and foal is essential as problems such as growth abnormalities can come about rapidly and occasionally downward adjustments are required (feeding the growing foal and young horse will be covered in the next months article).

Mares’ milk is poor at supplying some minerals, such as zinc and iron, copper and manganese.  These are laid down in the foal’s liver in the last 3 months of pregnancy. Adequate feeding then will reduce the complications this period of rapid growth can cause – especially to joints.

Lastly – never forget parasite control! Feeding worms is not only expensive, it can cause liver damage, colic and a failure to thrive that may just cause the failure of a pregnancy.

Foals exposed to some level of creep feed show less stress at weaning – their hindguts are better adapted for the change in diet. They also have a more reliable source of trace elements than grass alone. Foals that had creep while still with their mothers also show are more consistent level of growth post weaning – and fewer growth ‘spurts’ means less developmental joint disease (DJD).

Following weaning, it is often tempting to feed much more. But the youngster’s hindgut is only new to fibre digestion, and intake can be low – often causing the breeder to offer more cereal. High cereal diets, though, cause gastric ulcers, as does stress. The two in combination, as after weaning, can initiate a cycle of adolescent ulcers causing poor growth rates – and more food offered…  If intake is low, split into more frequent, smaller, offerings – and always if total formulated ration per day is more than 1% body weight.

Cereals are a high-glycaemic food. This means that they result in an escalation of blood glucose shortly after feeding, and a corresponding insulin surge. It is not proven, but widely believed to be true, that insulin is implicated in poor cartilage formation. Low cereal/high fibre diets are increasingly seen relevant for all horses, and never more so than while growing and developing their musculoskeletal systems.

Richard Stringer BVSc MRCVS of Stringer Equine Veterinary Practice