Nutrition for the pregnant and postpartum mare

Regarding horse soundness, Mexican equestrian traditional knowledge affirms that “horses are worth what they are, and do, whilst foals are worth what they will be, and will do”; and there is enough solid, current scientific evidence to confirm that, among other environmental factors, the nutrition of the broodmare during pregnancy and early lactation affects phenotype of her offspring at both short and long term, especially when nutritional disorders occur during critical periods of development.^{1, 2, 3, 4, 5, 6}

A critical period is a point in the life of an organism in which a specific environmental factor is likely to exert its greatest influence,⁷ just as it occurs in critical periods of development thru the prenatal and early postnatal life, in which nutritional derangements, and the resulting metabolic disorders,⁸ have a major effect on the anatomy, physiology, and behavior of the foal,9 then on its performance when adult.⁶

Since intrauterine growth is determined primarily by the supply of nutrients, both under- and overnutrition of the mare during pregnancy, cause profound effects on the development of body systems that are essential to cope with the extrauterine environment and to perform later in life (e.g. musculoskeletal, cardiovascular, gastrointestinal, nervous, metabolic and endocrine).^2,3,6 The mismatch between offspring phenotype and the environment¹ can be noticed just after birth, when assessing the health and soundness of the newborn foal, or perceived later in life,¹⁰ at some point in growth, foundation, training or work, when physical and mental effort is exerted. Whether physical or behavioral, the outcome has lifelong consequences for horsemanship.⁴

Therefore, considering that nutrient availability, transport, and partitioning during critical periods affect cell multiplication and differentiation, as well as tissue development and maturation, with the latter still during early lactation, it seems sensible to approach the nutrition of the broodmare from the concept of fetal programming;^4,6,11,12 particularly when reproductive technologies are implemented,¹³ due to their effects on fetoplacental and postnatal development.^2,3

Certainly, although the supply of nutrients and oxygen depends on both their availability in the mare and the functional capacity of the placenta,^4,12 through this lecture, the need of ensuring nutrient availability in the mare is highlighted, leaving placental function for further review.^2,3,12

Concerning nutritional disorders, under- and overnutrition, as well as macro and trace elements deficiencies or excesses, are commonly found in the equine world, because nutritional requirements and nutritional value of feedstuffs in horses are rarely estimated in practice. Undernutrition is the result of an inadequate supply of nutrients, although it can also result from malabsorption, impaired metabolism, loss of nutrients, or increased requirements due to disease or other environmental stresses.¹² Overnutrition has become a common condition in the horse industry as a result of excessive ingestion of nutrients, not only due to the disproportionate addition of concentrates and supplements but also to the misinformed introduction of some forages, whose contents of protein, minerals and non-structural carbohydrates may exceed horses natural needs. Likewise, mineral deficiencies, excesses, and imbalances, result from the poor application of available information on equine mineral nutriton.¹⁴

Because dietary management of broodmares is essential for breeding and successfully raising healthy foals,¹⁵ equine veterinary professionals^16,17,18 play a key role in providing nutritional advice according to life stage of individual equids, as well as in designing feeding programs to sustainably promote the health, welfare, productivity and performance of equine populations. Fortunately, there are educational programs,¹⁹ innovating methods,²⁰ and progressive technology,²¹ to enable veterinarians to clearly and confidently guide the horse industry in the proper use of feeding resources and the implementation of nutritional strategies.

A One Welfare approach,²² considering animal, human and environmental factors, facilitates the development of effective, affordable and sustainable nutritional programs. Animal aspects include breed, age, body weight, body condition, physiological state, and health status; whilst purposes of breeding, industry requisites, type of system, and management practices, are some human influences. Among environmental components, geography, climate, season, fauna, flora, diseases, resources, and facilities are most important.

The aim of a nutritional program is to guarantee that requirements for maintenance, fertility, pregnancy, and lactation are met. Implications of nutrition during pregnancy have already been discussed, so it is opportune to mention that nutrition for lactation is crucial, primarily, because the immediate neonatal period is a critical period of development,^3,5 during which maturation of some tissues takes place and, furthermore, because the mare has to reach her potential of milk production, with proper quality to feed a foal that, by weaning, has to be around eighty percent of its adult height and fifty percent of the expected adult body weight. Although other factors like age, parity and breed are involved, maternal nutrition influences colostrum quality, as well as milk yield and composition.^5,27 As an ultimate reason to warrant nutrition during lactation, it is the fact that most sectors of the horse breeding industry expect taking advantage of the natural ability of the mare to become pregnant again shortly after parturition, in order to produce a foal by the same, ecologically or economically, convenient season each year.

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