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Feeding Pregnant Mares

Feeding pregnant mares correctly and matching the nutrients to the grass, hay and haylage fed is the best way to build the best foal possible.

Without knowing the nutrient levels in the forage fed then it is difficult to know where best to start with protein and mineral supplementation.

Here at Forageplus, we would love to supply an off the shelf horse feed supplement for feeding the pregnant mare.  However, to get the strongest, healthiest and best foal possible, our statistical analysis of the hundreds of forage analyses we carry out for clients each year shows us that there is too much nutritional variation.  This variation in the levels of minerals and protein means that to provide the best start for the growing embryo you should test the forage your mare is eating.

feeding the young horses
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We prefer to advise clients to test the grass, hay and haylage their mare will be eating so that accurate feeding requirements can be determined and both the mare and foal can be provided with optimal nutrition throughout the pregnancy and beyond.

A mare needs to have access to the correct nutrients in the correct amounts and most importantly in the correct balance as the minute an egg is fertilised, growth in the form of cell division starts at a mind-blowing pace. From a single cell, within 11 months, a newborn foal will be born with over 100 trillion cells and each of these cells has its own special purpose and needs to be fuelled and built by accurate nutrition.

Feeding the pregnant mare with accurate nutrition as a developing embryo will lead to robust, healthy organs and body structures such as bones, tendons and ligaments.  The health of the future foal is in the breeder’s hands, there is a lot you can get away with without causing actual death but if you are truly interested in breeding a foal with a healthy long life ahead of it then giving it the best nutritional start right from the moment of conception is crucial.  You don’t just want your mare and foal to survive, survival is a goal but optimum health and development into a strong resilient adult have to be the discerning breeder’s goal.

young horse lying in the pasture
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Feeding pregnant mares: the first four months

Protein is the most important consideration in the first four months.  The foal grows to the size of a beagle during this time but the placenta is developing over this period and protein quantity and quality (meaning good access to all the essential amino acids) is critical.  Poor protein levels and quality have been shown to lead to low progesterone and possible losses in early pregnancy.

Protein for the pregnant mare is crucial

A guide is to work out what protein your pregnant mare is receiving by carrying out a forage analysis on the hay or haylage eaten so that you can determine the levels in the diet.  A 500 kg pregnant mare should be receiving around 900 grams of protein if fed a hay/haylage and cereal concentrate diet (we recommend oats).  The cereals will offer a good protein and amino acid profile.  A 500 kg pregnant mare on a purely forage-based diet, pasture or hay/haylage needs a greater protein level at 1100 grams.  This is because the quality of protein provided in forage will be of poorer quality than that in cereal.

A good quality forage for feeding the pregnant mare

Good quality forage is crucial when feeding pregnant mares. Be aware though that many forages are really quite low in protein 6-7% average and a pregnant mare will need an average of 11% protein in the diet to be able to keep herself at optimum health at the same time as building the new life within her. If the hay is under 11% protein then you will lose 100 grams of protein per 10 kg eaten for every 1% below 11.  This is why it is crucial to know exactly what protein level the hay or haylage you are feeding contains by testing it.  A stud farm we have dealt with had an as fed protein level of 3.7% so effectively a mare in foal in the winter was going to really struggle to maintain herself and probably the developing embryo will be compromised in its development. This won’t lead to death but it will lead to resilience issues when that foal grows into an adult horse.

young horse
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Mineral amounts when feeding pregnant mares

The Nutritional Research Council (NRC) does not recommend any increase in mineral intakes until the 7th month and you can perhaps go with this if your horse is already on a ‚Äėforage focused‚Äô horse feed balancer supplement where levels of minerals have been raised to 150% of the bare minimums recommended by the NRC and balanced to the forage eaten.¬† This approach matches the common frank and relative deficiencies in grass, hay or haylage and avoids the damaging problems caused by high antagonist minerals such as iron and manganese.¬† If your horse is not on this type of balancer then the bare minimums suggested by the NRC are just that ‚Ķ.. bare minimums and that in our opinion does not mean optimum health.¬† Even if the foal is only the size of a beagle, nutrients are needed to grow that life and support the growth of the placenta, if these nutrients don‚Äôt come from the diet then they will come from the mare but only if the mare has enough to give and why leave that to the chance of guessing if you want the best foal possible.

Feeding the pregnant mare: the first seven months

For the first 7 months of pregnancy, you want at least 150% of the NRC minimums with calcium and phosphorous at a ratio of 1.2 to 1.5.  This can be tricky as our forage analysis samples show that phosphorous is often very low in the forage we test and it becomes tricky to balance the high levels of calcium often reported. Sodium is also an issue with low levels in forage so you should supplement salt on a daily basis in the feed, a salt block is not enough as some horses will not touch or lick enough salt from a block. Feed at least 3 x 25 ml scoops of salt a day to promote good drinking and prevent dehydration.  Dehydration causes uterine irritability and increases the risk of colic and impaction.

Forage testing when feeding pregnant mares is important

Although we could supply some ballpark figures for each mineral for feeding the pregnant mare we actually believe it is very important to have forage tested to be precise.  This is because levels of iodine can vary widely in the UK, also selenium can be very variable.  If you have high iodine and add more to the diet this can lead to abortions and or goitre in foals, knowing the iodine levels in the grass, hay or haylage your mare is eaten then is most important.  In most of the forage, we test calcium tends to be high with phosphorous at very low levels, but some hays test with moderate calcium so it is difficult without testing hay to be completely sure.  If you want the very best foal possible we feel, here at Forageplus, that you should be concerned to be precise, test the forage the pregnant mare is eating and make sure the minerals are at optimum so the mare has optimum nutrition to pass on to the foal.

Vitamin amounts when feeding pregnant mares

B vitamins are very important for metabolic active tissues and dividing cells but there is currently no evidence of B vitamin deficiency in pregnancy. As long as the mare is eating a forage-based diet and eating well supplementation is not necessary. A mare with diarrhoea or with greatly reduced feed intake should be supplemented.

Vitamin C is crucial to the health of connective tissue and joint cartilage formation. Pregnant mares may benefit from extra Vitamin C even though all horses can synthesise vitamin C within the body as this may not be optimal for pregnancy.  Mares on green pasture do not need supplementation with vitamin C as green and growing grass contains plenty. If a pregnant mare is not on pasture however then supplementation of between 1000 to 5000 mg is good insurance.

If the hay being fed is not green or older than 6 months then it is wise to supplement vitamin A if a pregnant mare is not on green and growing pasture. Feeding 30,000 IU per 500 kg of bodyweight is wise.

Vitamin D should not need to be supplemented if the mare is exposed to sunlight through the warmer months and fed cured forage such as hay or haylage.  All forage contains a precursor from which horses can synthesise vitamin D, however, hay older than 12 months is likely to need supplementing with 300 IU/kg of the diet.

Vitamin E is crucial for a healthy and resilient immune system. It has recently been confirmed in a 2011 study from Copenhagen that increased levels of immunoglobins (antibodies) were seen in the colostrum of mares supplemented vitamin E in the last 4 weeks of pregnancy.  Their foals were also found to have improved vitamin E status and IgM levels.  Winter feeding where green and growing pasture is absent will result in very poor levels of vitamin E so this vitamin should be supplemented from the beginning of October right through to the end of April or until green and growing grass becomes the main part of the diet. Green and growing grass contain high levels of vitamin E.  The level of vitamin E fed in the Copenhagen study was over 4IU per kg of body weight which is twice the current NRC 2007 maintenance level.  You should always supplement a pregnant mare with vitamin E unless the mare is on good pasture.

young horses in the pasture
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Feeding pregnant mares: the last 4 months

The last four months of pregnancy are when the foal grows most in size.  At this point levels of protein and nutrients hold be carefully matched to provide at least 150% of the NRC 2007 minimum requirements and balanced to the forage fed. The balancing should take account of antagonist minerals which may block the uptake of very important trace minerals such as copper and zinc. The balancing should also pay to get attention to the levels of calcium and phosphorous in the forage being eaten so that the correct ratios of these minerals can influence the correct developmental growth in the foal.  Most off the shelf horse feed supplements and balancers will not address the frank or relative deficiencies in forage so this is why a forage test is crucial to provide the very best for both mare and foal.

If your mare will not eat enough forage in the last 4 months of pregnancy to supply energy and protein demands then you should have a plan to feed concentrates and increase slowly. Forageplus can advise you further on the best way to do this to keep the balance of the minerals correct in the diet.

Our top tip is that solid nutrition, informed through testing grass, hay or haylage is the only way to protect both your mare and foal.  Only an analysis of the forage eaten can provide a precise basis on which to decide the best feeding pregnant mares and the resulting health of the newborn foal.

View our recommended forage focussed balancers for pregnant mares here.

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