Feeding the brood mare- effects on the foal in-utero

Avoid any excess

The energy requirements of the brood mare start to increase gradually from the 6th month of  gestation. The breeder can then be tempted to feed the mare on a ration which is too rich, in the hope that it will optimise the development of the fœtus. But nutritional excesses are at present being incriminated in the onset of certain metabolic abnormalities in the foal, after bitrth.

To give an example, a high starch diet (from the 7th month of gestation to the 5th day of lactation) leaves a durable imprint on the energetic metabolism of the thoroughbred foal :  

• The glucose and insulin concentration in the blood are higher at 5 days old, and at one month old.
• The capacity to metabolize glucose is lower at one month old
• Sensitivity to insulin is reduced at 5 months old.

Even given over a shorter period of time, this type of diet can still have drastic and persistant effects. A trotter mare, fed on a high energy diet (from the 9th month of gestation up to foaling) decreases the foal’s capacity to metabolise glucose, and his sensitivity to insulin at 2 weeks old, as well as his insulin concentration in the blood at 2 weeks, 4 months and 10 months old.

It can be noted that neither of these two diets affected the weight of the foal at birth, but his energy metabolism was disrupted in the long term.

Type of energy

The type of energy contained in the ration could also worsen these problems. This is why suspicions nowadays are directed towards the traditional practice of giving hard feeds during gestation.

Consequently, the effects of supplementing the mare on cereals has been the object of two studies, one in the United States and one in France. To carry out these studies, mares kept either out at pasture or stabled were fed solely on forage (pasture or hay), or also with cereals (either mixed cereals or only on rolled barley) as from the 7th month of gestation. When the mares were not supplemented, weight loss due to a higher use of stored fat was noted, compared to the supplemented mares, who were heavier and fatter. Neither had an effect on the weight of the foal at birth, but providing cereals during gestation did have an effect on the foal’s hormonal function. The concentration of leptin* in the blood was lower in the first 18 hours after birth, and the tolerance to glucose* increased 3 days after birth. This might affect the foal’s feeding behaviour, although this parameter was not measured in these particular studies. At six months old, the foals of the mares who had been supplemented were more likely to present osteochondrosis lesions. This observation had already been brought to light in an epidemiological study. This study demonstrated that a Belgian warmblood mare fed on concentrated feeds during gestation, had a higher risk of giving birth to a foal presenting osteochondrosis lesions (compared to mare being fed solely on forage).

What relationship could there be between hard feed and osteochondrosis ?

American researchers demonstrated that foals producing more insulin after feeding, are more likely to present osteochondrosis lesions, than those producing low quantities. It has also been shown in vitro that cartilage cells are particularly sensitive to insulin right from foetal stage in the foal. Insulin therefore appears to have an effect on the proliferation of cartilage cells, preventing, when present in large quantities, bone cells from replacing cartilage cells during bone growth. A French study also showed that mares producing more insulin after feeding during gestation were more likely to produce foals suffering from osteochondrosis.

Colostrum

The quality of colustrum (concentration of anti-bodies required for immune defenses of the foal) is deteriorated in mares supplemented with cereals. Two French studies have noted a correlation between poor quality colustrum and osteochondrosis in foals. However, there is to date no explanation for this link. Nevertheless, these observations emphasize the importance of colustrum quality on the long term development of the foal, which can be modified by the mare’s feed during gestation.

The placenta

The placenta also appears to have a determining effect in these cases. Although they present no difference in weight, volume or surface, the placenta of mares having been supplemented on cereals present vascular alterations. The placenta vessels, essential for the transfer of nutrients from the mare to the foal are smaller in volume. They appear to be less capable of increasing blood flow to the foal. The placenta also presents signs of inflammation. Non infectious inflammation can lead to alterations in the cell function, but also vascularisation. By altering the placenta’s action, too much starch given to the gestating mare can also deteriorate the foal’s health in the long term. It is therefore not so much the fact of supplementing the mare as such, but the amounts of starch and sugar provided with each feed that lead to an increase in insulin production by the mare, to the detrimlent of the placenta functionning properly, and consequently to the foal’s development.

Overweight : when overfeeding becomes chronic

In horses, the definition of obesity and being overweight is specific. As herbivores, in a natural free roaming state, their body weight changes with the time of year. It evolves following the quality of the grass. It is therefore quite normal for a horse to be overweight in Spring, and to lose weight in winter. A horse can therefore be considered to be overweight, or even obese, when his body condition remains stable throughout the year.

Obesity is a bane in the equine sector. Depending on the country, the breed, the discipline and the studies, up to 72 % horses are considered to be overweight. Just the fact of being on a breeding stud, is even considerd as a factor of risk.  For an adult horse, being overweight is associated to metabolic conditions, to diseases such as laminitis, and to a decrease in sports performance. But it also has consequences on the development of the foal.

Whatever they are fed on, mares who are overweight during gestation produce foals who are less sensitive to insulin at 6 months and 18 months old. They are more at risk of having osteochondrosis lesions at 12 months old and have increased systemic non-infectious inflammation up to 6 months old. The mare’s weight therefore has a long term impact on the foal’s health, and can have an impact on his performance. Reduction in sensitivity to insulin is associated to intolerance to exercise. Foals born to overweight mares, could consequently have more problems restoring and using their muscle glycogen reserves, which decrease their athletic capacity.

It is therefore essential to keep a measure of the pregnant mare’s body condition, which should never be above 4 on a scale of 5 during pregnancy. Do not forget that a healthy mare will store energy reserves at the start of gestation, to use them towards the end, when the growing foal’s needs are greatest. So a slight loss of weight in the last three months of gestation can be expected. The mare’s body condition should be around 3 at the foal’s birth.

What about under-feeding ?

At what stage does under-feeding the mare affect the foal’s development ?

Cases of a foal losing weight at birth are rare. Apart from very substantial changes due to embryo transfers, only very considerable under-feeding associated to an illness can lead to a decrease in the foal’s weight at birth. This was the case in a British study, where the mares had strangles half-way through pregnancy, and stopped feeding for several days. Altough the foals were measured as being smaller at birth, the effects of this marked under-feeding in the long term were not however documented.

In the two studies mentioned above, the mares who were solely fed on forage during gestation did not get enough energy. They were however considered to be moderately under-nourished, since their body condition was not « thin » at the birth of the foal. This under-feeding, although it had no effect on the weight at birth, did however modify the growth and metabolism, since at one year old, these foals were noted to have delayed testicular maturity, at 18 months old, the canons were not as wide in diameter and they were more resistant to insulin. Testicular maturity does not however give any information as to the future fertility of the foal. In the same way, the width of the canon bone does not give any informationas to the bone density or resistance of the foal’s bones to effort.

In this case, it appears that the placenta compensates for the lack of nutrients provided, via an increase in the volume of the vessels, and the use of sources other than carbohydrates (fatty acids and amino-acids) to produce its own energy. This enables the foal to be born at a normal weight and size, but it does lead to long term alterations in the foal’s metabolism and development.

When the mare is under-nourished during gestation it is also to the detriment of the foal’s development. Even if the foals appear to develop properly in utero, they present a delayed maturity later on.

Conclusion

In numerous cases, the quality of hay is not sufficient to cover the energy and protein requirements of the pregnant mare. Therefore, it not a question of dispensing with hard feed completely, but rather limiting high starch content during gestation.

Fractioning the ration of concentrates as much as possible decreases the mare’s insulin production.

Moereover, monitoring her body condition so that the mare is not overweight, but is still getting the necessary amount of energy to support the foal’s growth and development is important. It is paramount to preserving the mare’s health, fertility, and also the health of the foal to be born.

Both an excess or a lack of trace-elements and vitamins can be harmful to the mare, they are just as harmful to the developing foal while in the mare’s womb. The brood mare’s requirements in trace-elements and vitamins are more or less well-known, and the effects of their intake during gestation, on the foal after birth have been very little studied. To date, three tracks have been partially explored:

Omega 3 fatty acids

Fresh grass is a good source of omega 3 fatty acids for horses. It appears therefore that these fatty acids are important for the development of the embryo, and the mare’s uterus at the time of insemination.

Two American studies have in fact shown that supplementing a traditional ration (cereals/ hay) with omega 3 fatty acids from seaweed, from 47,5 days before to 12,5 days after insemination seems to improve the uterine environment and the embryo development, for better capacity of the embryo to become implanted.

Later on, supplementing the pregnant mares with fish oil two to three months before foaling leads to an increase in the omega 3 fatty acids concentration in both the dam’s and the foal’s plasma, as well as in the colostrum and milk. This supplementation is useful whatever the situation, as omega 3 fatty acids (present in large amounts in seaweed and fish) are essential to the foal’s cognitive development. They also have high anti-inflammatory effects and protect the cardio-vascular system. In overweight gestating mares, the omega 3 fatty acids content is lower in the colostrum, but also in  the foal’s plasma at birth, before suckling. Foals born to overweight mares also have a lower omega 3 fatty acids content in their plasma up to at least three years old, this profile being associated to sterile inflammation, and decrease in sensitivity to insulin noted during growth.

Selenium

Selenium is a powerful anti-oxydant, which protects biomolecules against damage linked to the free radicals of oxygen. Supplementing with selenium based supplements towards the end of gestation, when maternal metabolic activity is greratest, appears to be particularly relevant. In quarter horse brood mares kept at pasture (either with or without any hard feed), daily oral supplementation with organic selenomethionine(« selenium enriched yeast »), from the 7th month of gestation to foaling, is sufficient to ensure a high selenium content in the blood and muscle of the foal up to 2 months old. The action on the immune system remains to be demonstrated, but the effect on the hormonal system is proven, as supplementing the mare with selenomethionine lowers the leptin concentration in the foal’s blood in the first 18 hours after foaling. Selenium is essential to the foal’s proper development. A high deficiency during gestation has been linked to white muscle disease at birth, generally fatal to the foal. Colostrum is poor in selenium, therefore the foal receives a large part of this trace elemnt via placenta transfer.

Copper

Copper deficiencies have been implicated in the development of juvenimle osteoarticular abnormalities. Moreover the copper available to the suckling foal is the copper stored during gestation. Thus, Warmblood foals with the highest hepatic stores of copper at birth are less likely to develop osteochondrosis, and if they do it is of lesser severity from 5 to 11 months old. Supplementing the mare in copper should therefore be carefully monitored, to ensure optimum healing of early lesions of the foal’s cartilage. In thoroughbred mares, orally supplementing with copper, from the 6th month of pregnancy up to foaling, decreases the incidence of cartilage lesions in foals at 5 months old, whereas no improvement is noted when only the foal is supplemented from birth to 5 months old.

Vitamin E

Vitamin E is another anti-oxidant which promotes the passive transfer of immunoglobulins from the mare to the foal. In Danish Warmblood mares, daily oral supplementation in  RRR-α-tocopherol (natural form of vitamin E)during the last 5 weeks of gestation, enriches colostrum, milk, and the foal’s blood in vitamin E for the first 3 days after birth and increases the concentration of immunoglobulin M in the foal’s blood at 3 days old. Vitamin E is therefore an immunity booster for the newborn foal.

Maternal signals during gestation interact with the foal’s genotype. This is now considered a certainty, they contribute actively to conformation, energy metabolism, cardiovascular system, osteoarticular condition, and immune response of the foal after birth. Correct management of the brood mare is a determining factor in the production of horses with desirable characteristics, even if it is early days to give definite recommendations to breeders. You can also consult the fact sheet : Prepare the foal’s health during gestation.

Indeed, numerous questions remain. The mare’s age, breed , but also her status as a broodmare can interact with the environment she is in. A young first foal mare will not react in the same way to high starch content in her feed, as an older mare having had several foals. Even if today, it is commonly admitted that a first foal mare usually gives birth to a lighter weight, smaller, and less mature foal, at least up to 18 months old, than an older mare having had several foals, the differences  between the general or specific requirements between the two categories have not yet been studied. Moreover, practically none of the studies have been pursued up to adulthood, and many aspects are still unexplored.

The work conducted in other animal species show that the environmental effects during gestation often appear in the ageing individual, or when confronted to a revealing environment (such as a ration which is too rich or with deficiencies) These effects are also likely to be transmitted to future generations.