Maternal Nutrition and Fetal Programming in Horses
How a Broodmare’s Nutrition and Health Can Influence Her Foal’s Lifelong Health and Performance
The health of a foal begins long before foaling. During approximately 11 months of pregnancy, the mare supplies oxygen, energy, amino acids, vitamins, minerals, hormones and the environment in which every organ system forms. Her genetics matter, but so do her nutrition, body condition, health and placental function.
This is the basis of developmental programming, part of the field called the Developmental Origins of Health and Disease, or DOHaD. Conditions during early development can influence how the body is built and functions later. In horses, those influences may affect birth weight, skeletal and muscle development, metabolism and immune function.
Developmental programming does not guarantee success or failure. Genetics, foaling, colostrum, postnatal nutrition, exercise, disease, injury, training and daily management continue to shape the horse. Prenatal management establishes part of the foundation on which those later influences act.
Owners who are still deciding whether a mare should enter a breeding program may also find Broodmares: How to Select the Right Mare for Breeding useful. Once a breeding date is known, the free Horse Gestation Calculator can help organize expected milestones and the likely foaling window.
What Is Developmental Programming?
Developmental programming describes persistent changes in the structure or function of organs and tissues caused by conditions experienced during sensitive stages of development. The fetus adjusts its growth to its environment. Some adjustments may help it cope with limited nutrients or oxygen before birth but carry consequences later.
The process does not normally change the foal’s DNA sequence. It can affect how genes are regulated, how many cells form, organ structure, blood-vessel development, hormone signaling and tissue responses to nutrients. Epigenetics, which means the persistent regulation of gene activity without a change in DNA sequence, is one mechanism, but not the only one.
Timing matters. An organ undergoing rapid development may be particularly sensitive to a nutritional shortage, excess or disease challenge. The same exposure at another stage may have a different effect.
Systems that may be influenced include:
The skeleton, joints and growth plates
Skeletal muscle
Tendons and ligaments
The pancreas and insulin-regulating systems
Fat storage and energy metabolism
The cardiovascular system
Immune tissues and inflammatory responses
The placenta itself
Overall fetal growth and birth weight
Did You Know? A normal birth weight does not prove that every organ developed identically. Research on maternal overnutrition has found changes in foal pancreatic tissue even when birth weight did not differ between groups. Birth weight is useful information, but it is only one measure of prenatal development.
The Mare’s Influence Beyond Genetics
A foal receives roughly half of its nuclear DNA from the mare and half from the stallion. The mare’s contribution extends much further. She provides the uterus, the placenta’s maternal blood supply, nutrients, oxygen and hormonal signals throughout gestation. After delivery, she supplies colostrum, milk, protection and the foal’s earliest social experiences.
The uterus also places a physical limit on growth. Embryo-transfer research involving Thoroughbred and pony mares demonstrated that maternal size influenced placental development and birth weight, even when the embryo came from a larger or smaller breed. This provided strong equine evidence that the uterus can modify the expression of genetic growth potential.
Both parents contribute genes affecting size, conformation, metabolism, soundness, temperament and athletic traits. Choosing suitable parents and managing the mare correctly are separate responsibilities. Management cannot erase inherited risk, and good genetics cannot compensate for every pregnancy problem.
The Placenta: The Working Link Between Mare and Foal
The equine placenta is diffuse: its exchange surface extends across much of the uterus. Thousands of microscopic structures called microcotyledons create close contact between maternal and fetal tissues. Oxygen and nutrients move toward the fetus, while carbon dioxide and waste products move away.
Placental size, structure, blood flow and efficiency affect what reaches the foal. A balanced ration cannot overcome severely impaired placental function. Uterine disease, placentitis, twins, abnormal attachment and poor blood flow can restrict growth, disturb maturation or contribute to premature delivery.
Warning signs during pregnancy—including premature udder development, lactation before the expected time, vulvar discharge, fever, colic, depression or a sudden change in the mare’s condition—deserve prompt veterinary attention. Some affected mares show few obvious signs, which is why scheduled reproductive examinations remain important for higher-risk pregnancies.
Did You Know? The equine placenta prevents meaningful transfer of maternal immunoglobulins before birth. A foal may develop immune cells in utero, but it is born with very little circulating antibody protection and must absorb antibodies from colostrum soon after delivery.
Maternal Nutrition During Pregnancy
Maternal nutrition is one of the most manageable influences on fetal development. The goal is to supply appropriate energy and essential nutrients while maintaining healthy body condition and avoiding major imbalances.
Start with The Basics of Equine Nutrition. Needs vary with weight, age, breed, body condition, environment, forage, gestation stage and lactation. A generic scoop measure cannot account for those variables.
Energy: Enough, but Not Excessive
Energy supports the mare’s maintenance, activity, thermoregulation and pregnancy. Requirements do not increase equally across the entire pregnancy. During early and mid-gestation, a healthy mare may maintain appropriate condition on a diet similar to her pre-pregnancy ration. Fetal weight gain accelerates in the final trimester, and the mare’s need for energy, protein, minerals and certain vitamins rises with it.
If energy intake is inadequate, the mare uses her own fat and muscle. Depending on severity and timing, undernutrition may restrict fetal growth, alter organ development, reduce the foal’s energy reserves and limit milk production. Thin mares also have less reserve for illness, cold weather, foaling and lactation.
Excess energy creates different problems. Obesity strains the mare’s feet and joints and may accompany insulin dysregulation or inflammation. Equine studies have linked maternal obesity with altered insulin responses, low-grade inflammation and more osteochondrosis lesions in young offspring. Other work found altered pancreatic islets in foals after late-gestation overfeeding despite similar birth weights. These findings do not allow an individual foal’s future to be predicted from the mare’s condition alone.
Avoid crash dieting a pregnant mare. If substantial weight loss is needed, it is safer to address it before breeding. During pregnancy, ration changes should be gradual and supervised by a veterinarian or qualified equine nutritionist.
Protein and Essential Amino Acids
Protein supplies amino acids used to build muscle, bone, connective tissue, enzymes, hormones and organs. Quality matters as well as crude-protein percentage. Essential amino acids must come from the diet. Lysine is typically the first limiting amino acid considered in equine rations; methionine and threonine may also matter.
A mare needs usable amino acids, not an inflated crude-protein number. Forage analysis, protein source and the specifications of a properly formulated broodmare feed are more informative than an ingredient name alone.
Most muscle fibers are established before birth; postnatal growth occurs largely through enlargement of existing fibers. Livestock evidence shows that restricted maternal nutrition can alter fetal muscle development. Direct long-term equine evidence is limited, so precise claims about later speed, strength or endurance require caution.
Explore the Interactive Horse Muscle Map for an anatomical overview, or use the Equine Body Muscle Score guide to distinguish muscle condition from fat coverage in the mare.
Minerals and Skeletal Development
The fetal skeleton, joints and cartilage require a balanced supply of macro- and trace minerals. Calcium and phosphorus are major structural components of bone. Copper contributes to enzymes involved in connective-tissue formation, while zinc, manganese and magnesium support many aspects of tissue growth and metabolism. Selenium participates in antioxidant systems, but its safe range is relatively narrow and excessive supplementation can be toxic.
Mineral balance is as important as quantity. One mineral can interfere with another, and overlapping fortified feeds and supplements can create excesses. Forage, commercial feed, ration balancer, loose mineral and supplements must be evaluated as one diet.
Copper has received attention because inadequate status has been associated with abnormal cartilage development. Developmental orthopedic disease is multifactorial: genetics, growth rate, energy, mineral balance, exercise and trauma interact. Copper supplementation cannot prevent every lesion.
The Interactive Horse Skeleton provides a useful visual reference for the bones and joints being discussed.
Vitamins, Antioxidants and Fatty Acids
Vitamins A, D and E support growth, bone metabolism, immunity and antioxidant protection. Needs depend on pasture access, forage storage, region and the total ration. Fresh pasture may supply substantial vitamin E and beta-carotene, while levels decline during hay storage.
Essential fatty acids contribute to cell membranes and inflammatory signaling. Research continues into possible effects of maternal omega-3 intake on pregnancy, colostrum and immunity. Results from one supplement should not be generalized to every product.
Correct a documented or likely shortfall without creating an excess. Selenium illustrates why: soil and forage levels vary greatly, and too much is toxic. Use forage analysis and a total-ration review.
Forage First, Then Balance What Is Missing
Good-quality forage should form the foundation of most broodmare diets, supporting chewing, gut motility and hindgut microbes. Quality means clean, palatable and nutritionally appropriate—not simply green.
A forage analysis can reveal energy, protein, fiber, sugar, starch and minerals. Use the comparison of orchard grass, timothy and alfalfa to understand common differences, or the Alfalfa Pellet Feeding Planner for preliminary calculations. The complete broodmare ration still needs review.
Practical feeding points include:
Weigh forage and concentrates instead of relying on scoops or flakes.
Introduce feed changes gradually.
Split larger concentrate allowances into several meals.
Provide constant access to clean water and appropriate salt.
Prevent competition from more dominant horses.
Store feed safely and discard moldy or contaminated forage.
Review the entire ration before adding another supplement.
Reassess the diet as body condition, pasture and pregnancy stage change.
The Hay Net and Slow Feeder Selector may help mares that eat too quickly or go too long without forage. Hang and maintain nets safely to limit entanglement risk.
Body Condition Is a Management Tool
Body condition scoring estimates fat coverage at six areas. It does not measure fetal growth, muscle or diet quality, but it tracks change over time. A Henneke score around 5 to 6 out of 9 is a common target for many broodmares, adjusted for breed, age, metabolism and veterinary needs.
A score of 5 is moderate: ribs are not obvious but can be felt, without a sharp outline or heavy fat deposits. A 6 has slightly more cover. Learn the landmarks in Body Condition Scoring, and use the Horse Weight and Body-Condition Estimator for records.
Score and photograph the mare regularly. Winter coat can conceal weight loss, and a late-term abdomen can distract from thin ribs, neck and topline. Assess fat and muscle separately.
Did You Know? Pregnancy size and body condition are different measurements. A mare can have a very large abdomen and still be losing fat and muscle. Feel the standard scoring areas rather than judging condition from the belly.
Because nutritional status changes gradually, records are especially valuable. Weigh or tape the mare, score her condition and muscle, photograph her, and note forage, concentrates, supplements, pasture and health events at regular intervals. A single observation can mislead; a trend can show that the ration or medical plan needs attention before visible weight loss, obesity or poor performance becomes established.
Maternal Health Can Change the Fetal Environment
Nutrition cannot be separated from health. Pain, fever, respiratory disease, gastrointestinal disease and reproductive infection can reduce intake or alter the mare’s hormonal and inflammatory state. Severe parasitism can contribute to poor condition, anemia or protein loss. Dental disease may prevent an otherwise adequate ration from being chewed and used effectively.
Routine care includes dentistry, hoof care, vaccination, parasite control and veterinary monitoring. Horse Teeth and Floating explains oral health and feed use. The Horse Deworming Schedule by Region and Risk and Deworming Schedule Planner can support an individualized veterinary plan.
Mares with Equine Metabolic Syndrome, insulin dysregulation, PPID, chronic laminitis or another long-term condition need closer planning. Read Equine Metabolic Syndrome and Laminitis in Horses, then work with the veterinarian on medication, diet and monitoring. Pregnancy changes the risk assessment for some products.
Correctly timed vaccination protects the mare and can increase specific antibodies in colostrum. Schedules vary by region, exposure and product. Review the Horse Vaccination Schedule and 5-Way Vaccine Planner, but follow the veterinarian managing the pregnancy.
Stress, Housing and Exercise
Stress activates cortisol and other responses. In several species, sustained maternal stress is associated with altered fetal growth, metabolism, immunity and behavior. Equine evidence is less complete, so ordinary short events should not be treated as proof of permanent harm. Reduce chronic, avoidable stress.
Sources include illness, pain, repeated transport, weather extremes, abrupt social disruption, overcrowding, feed competition and poor housing. Stable groups, predictable routines and sufficient forage help.
Daily movement supports fitness, mobility, gut function and weight control. Healthy mares often benefit from turnout or controlled exercise suited to gestation stage, footing and health. Veterinary restrictions apply with problems such as placental disease, lameness, colic, twins or signs of premature delivery.
How Prenatal Conditions May Affect Major Body Systems
Bone, Cartilage and Growth Plates
Fetal growth accelerates markedly during late gestation, when substantial skeletal mineral accumulation and tissue maturation occur. A balanced maternal ration helps supply the raw materials for bone and cartilage, but developmental orthopedic disease cannot be reduced to one missing mineral.
Developmental orthopedic disease, or DOD, is an umbrella term for disorders involving the developing bones, joints and growth plates of foals and young horses. Conditions commonly discussed under this heading include:
Osteochondrosis and osteochondritis dissecans (OCD): abnormal endochondral ossification can leave thickened or damaged cartilage; fragments may separate within a joint.
Physitis: inflammation or enlargement around an active growth plate, often seen as swelling near the ends of long bones. Read Epiphysitis, or Physitis, in Young Horses for a detailed explanation.
Angular limb deformities: deviation of a limb to the inside or outside when viewed from the front or behind.
Flexural limb deformities: abnormal joint posture associated with imbalance in the functional length or tension of the musculotendinous unit; the limb may appear too upright, contracted or excessively extended.
Some conditions are present at birth; others emerge during growth. Genetics, uterine position, prematurity, illness, trauma, rapid growth, nutrition and exercise may contribute. A correctly fed mare can still produce an affected foal requiring an individual veterinary and farrier plan.
Muscle, Tendons and Athletic Capacity
Muscle-fiber formation occurs primarily before birth, while tendons, ligaments and their attachments also develop. Disruption could influence later function, but athletic performance is too complex to trace to maternal nutrition alone.
After birth, exercise, nutrition, hoof care and training continue shaping the musculoskeletal system. Youngstock management determines how well the foal uses its prenatal foundation.
Metabolism and Insulin Regulation
The fetal pancreas, liver, skeletal muscle and fat tissue help establish how the body will handle glucose and store energy. Maternal overnutrition and obesity are under particular study because they may expose the fetus to altered glucose, insulin, lipid and inflammatory signals.
Equine experiments have found insulin resistance at some ages, inflammation, osteochondrosis lesions and altered pancreatic development in offspring of overfed or obese mares. Studies are often small, and findings do not always persist. Obesity is a meaningful avoidable risk, not a prediction of the foal’s future.
Immune Development and Colostrum
The immune system begins developing before birth. Maternal nutrition supports immune cells, lymphoid tissues and antioxidant defenses. Maternal inflammation may also matter, but long-term equine consequences remain under study.
At birth, attention shifts to colostrum. The intestine absorbs large antibody molecules efficiently for only a limited period. Poor colostrum, delayed nursing or inadequate intake can cause failure of passive transfer and serious infection risk. The Complete Foaling Kit and Newborn 24-Hour Protocol provides a structured record.
Did You Know? The newborn foal’s first effective “vaccination” is timely intake of good-quality colostrum. Pre-foaling vaccination of the mare supports antibody concentration in colostrum, but it cannot help if the foal does not nurse and absorb enough.
Does Maternal Nutrition Determine Athletic Performance?
No prenatal measurement predicts future performance. Athletic ability reflects genetics, conformation, soundness, temperament, training, opportunity and injury. Maternal nutrition influences contributing systems, but its effect in an individual is difficult to separate from postnatal life.
Good broodmare care supports an appropriate developmental environment. No specific supplement can promise speed, stamina, jump or trainability. Aim for normal development, not exaggerated growth.
A Practical Broodmare Management Plan
Before Breeding
Arrange a physical and breeding-soundness examination.
Review reproductive history, chronic disease, medication and previous foaling problems.
Correct significant dental and hoof problems.
Record weight, body condition and muscle score.
Analyze the main forage and balance the total ration.
Review vaccination, parasite control and biosecurity.
Address obesity or poor condition gradually.
Decide how pregnancy checks, emergencies and foaling will be managed.
Early to Mid-Gestation
Confirm pregnancy and follow the veterinarian’s examination schedule.
Avoid automatically increasing concentrates because the mare is pregnant.
Maintain consistent forage access and an appropriate body condition.
Watch for weight or muscle loss beneath seasonal coat changes.
Make dietary changes gradually and document them.
Keep routine hoof, dental and preventive care current.
Investigate fever, discharge, colic, loss of appetite or sudden behavioral change.
Late Gestation
Recalculate the ration as fetal growth and nutrient demands rise.
Confirm that protein quality and mineral balance suit a broodmare, not merely an idle adult horse.
Monitor the mare’s condition frequently without encouraging obesity.
Review vaccine timing, foaling facilities and emergency contacts with the veterinarian.
Watch for premature udder development, milk production or vulvar discharge.
Prepare colostrum and newborn contingency plans before they are needed.
Use The Horse’s Vital Signs to refresh normal ranges and measurement methods.
The Horse Tracker can keep breeding dates, pregnancy checks, feed changes, body-condition records, vaccinations and foaling information together. Consistent records reveal trends that memory misses.
Did You Know? A mare’s average due date is only an estimate. Normal equine gestation varies widely, and the mare’s own previous foaling pattern may be more informative than a single 340-day calculation. Read the Horse Gestation Period guide when planning the foaling watch.
What We Know, and What We Are Still Learning
Evidence supports several practical conclusions. The uterine and placental environment influences fetal growth. Both undernutrition and overnutrition can create problems. Maternal obesity has been associated with measurable metabolic, inflammatory and orthopedic outcomes in equine offspring. The total ration needs adequate energy, quality protein and correctly balanced minerals, particularly as growth accelerates late in pregnancy. Maternal health and placental function can affect how effectively nutrients reach the fetus.
Important questions remain. Equine pregnancies are expensive and lengthy to study, and following horses through years of training is difficult. Many studies include relatively small numbers. Breed, mare age, management, sire genetics, pasture, foaling season and postnatal care can all influence results. Findings from sheep, cattle, rodents or humans help researchers identify mechanisms, but they cannot automatically be applied to horses.
The most defensible management approach is therefore steady and practical: keep the mare healthy, maintain appropriate condition, base the ration on measured forage and total nutrient intake, prevent avoidable disease and stress, and respond early when something changes. This supports normal development without making promises the science cannot yet support.
Conclusion
A broodmare shapes her foal through both inheritance and environment. Across gestation, her uterus and placenta regulate the supply of oxygen and nutrients from which the foal’s skeleton, muscles, organs, immune tissues and metabolic systems develop. Severe shortages can restrict development, while chronic excess and obesity can also produce measurable effects.
Good broodmare management is deliberate rather than complicated. Feed quality forage, balance the full ration, monitor body condition and muscle, maintain veterinary and preventive care, provide safe exercise and housing, and investigate warning signs promptly. These practices cannot decide the foal’s destiny, but they reduce avoidable risk and give the foal a sounder biological starting point.
Selected Scientific References
Swanson RM, et al. Livestock models of maternal nutrition and developmental programming. Journal of Developmental Origins of Health and Disease. 2026;17.
Allen WR, Wilsher S, Turnbull C, et al. Influence of maternal size on placental, fetal and postnatal growth in the horse. I. Development in utero. Reproduction. 2002;123(3):445–453.
Peugnet P, Robles M, Wimel L, et al. Maternal obesity increases insulin resistance, low-grade inflammation and osteochondrosis lesions in foals and yearlings until 18 months of age. PLOS ONE. 2018;13(1).
Bradbery AN, Coverdale JA, Hartz CJ, et al. Effect of maternal overnutrition on predisposition to insulin resistance in the foal: Maternal parameters and foal pancreas histoarchitecture. Animal Reproduction Science. 2021;227:106720.
Karren BJ, Thorson JF, Cavinder CA, Hammer CJ, Coverdale JA. Effect of selenium supplementation and plane of nutrition on mares and their foals. Journal of Animal Science. 2010;88(3):991–997.
National Research Council. Nutrient Requirements of Horses, Sixth Revised Edition. National Academies Press; 2007.
Fowden AL, Forhead AJ. Endocrine mechanisms of intrauterine programming. Reproduction. 2004;127(5):515–526.
Henneke DR, Potter GD, Kreider JL, Yeates BF. Relationship between condition score, physical measurements and body fat percentage in mares. Equine Veterinary Journal. 1983;15(4):371–372.
Frequently Asked Questions
What is fetal programming in horses?
Fetal or developmental programming occurs when conditions during early development produce lasting structural or functional changes. Maternal nutrition, health, placental function and hormones may influence fetal growth, metabolism, musculoskeletal development and immunity.
Does developmental programming change a foal’s DNA?
It generally does not change the DNA sequence. It can alter gene regulation, cell numbers, organ structure and metabolic or hormonal responses. Epigenetic regulation is one mechanism.
What body condition should a broodmare have?
A Henneke score around 5 to 6 out of 9 is a common target. Adjust it for breed, age, metabolic status and medical history with veterinary or nutritional guidance.
When does a pregnant mare need more feed?
Requirements rise most during the final trimester and again during lactation. Not every mare needs grain; adjust her diet according to body condition, forage analysis and the complete ration.
Can an obese mare affect her foal’s future metabolism?
Research indicates that maternal obesity can influence insulin regulation, inflammation and pancreatic development. Individual outcomes remain unpredictable, but maintaining appropriate condition reduces avoidable risk.
Can copper prevent developmental orthopedic disease?
No. Copper supports connective tissue and cartilage, but DOD has many causes, including genetics, growth, energy intake, mineral balance, exercise, trauma and disease. Excess copper may also unbalance the ration.
Is alfalfa safe for pregnant mares?
Alfalfa can supply protein, calcium and energy. Its calcium must be balanced with phosphorus and trace minerals. Base its use on forage analysis, the mare’s condition and the total diet.
Can a mare receive vaccinations and dewormers during pregnancy?
Pregnant mares commonly receive selected vaccines and parasite treatments, but choice and timing matter. Use products approved by the attending veterinarian and follow their labels.
How does the placenta affect fetal growth?
The placenta exchanges oxygen, nutrients and waste between mare and fetus. Its size, microscopic surface, blood flow and health affect fetal support. Placentitis can compromise growth or cause premature delivery.
Why is colostrum so important if the mare was well fed?
The equine placenta provides little antibody protection before birth. The newborn must absorb high-quality colostrum quickly. Prenatal nutrition supports development but cannot replace passive transfer.
Will excellent broodmare nutrition produce a better athlete?
It supports normal development and reduces avoidable risk, but cannot guarantee success. Performance also depends on genetics, conformation, soundness, temperament, training and management.
Who should formulate a pregnant mare’s diet?
Start with the veterinarian, especially for medical or reproductive problems. A qualified equine nutritionist can balance the ration using weight, condition, forage analysis, feed labels and pregnancy stage.
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