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What to Feed a Late Term Pregnant Mare

As the calendar clicks into another new year, we start to plan what to feed a late-term pregnant mare as we are entering the foaling season. There is always pressure in the thoroughbred industry in particular for foals to be born early in the year and indeed some are springing up already for their January due dates.

Nutrition of the pregnant broodmare is most important in the last trimester, the ninth, tenth and eleventh months. The nutrient requirements have been increasing steadily to this point but now the foetus is about to put on a big growth spurt. Pregnancy is particularly hard work and the mare needs to be able to maintain her own body condition; grow the foetus, grow the placenta, additional uterine, and mammary tissue and then maintain the foetus, placenta and uterus in optimum condition.

The exact nutritional needs of the mare will depend on individual factors such as breed, due date, body condition, and age etc. Native breed types due to foal in early summer may indeed meet all of their requirements through good pasture or perhaps adding just a small amount of stud balancer to provide the vitamins and minerals required. Non-native mares and early foaling mares will need added vitamins and minerals but also a higher intake of calories and protein.


Maternal malnutrition can have serious implications, causing impaired neonatal lung defences, muscle failure, bone or cartilage malformation, cognitive failure, and cardiovascular and endocrine abnormalities. The under nourished foetus will adapt to survive, this is effective in the short term but is likely to cause long-term health implications. Even though the foal may appear healthy, issues can manifest later in life. As such as recurrent airway obstruction (RAO), exercise-induced pulmonary haemorrhage (EIPH), and heart disease, all of which dramatically limit athletic ability.

Nutritional factors can combine with genetic predisposition to cause developmental orthopaedic diseases such as osteochondritis dissecans (OCD) in foals through alteration of normal growth processes.


Overfeeding can cause as many problems as uunderfeeding Obesity in broodmares can lead to various diseases of the mare herself, such as endocrine, metabolic disorders and laminitis. (Although laminitis in late pregnancy and postpartum is not necessarily caused by feeding. Veterinary advice should be sought immediately.)

There is increasing evidence that obesity in the pregnant broodmare can also lead to the foetus developing too much adipose tissue, fat, which may affect the development and future athletic performance of the foal. Some studies suggest a link with developmental oorthopedicdiseases.


Late pregnancy requires particularly increased levels of energy, protein, calcium, phosphorus, copper and vitamins A and E, as well as a balanced source of other vitamins and minerals.


Feeding additional concentrate will increase the energy provided by the diet. A significant calorie intake is required to maintain the high work rate of the body. Often mares in the last month of pregnancy will have reduced appetite because the foal is taking up so much space in the abdomen.

These mares will benefit from adding vegetable oils to the diet, this increases energy intake but not bulk in the feed. Vegetable oils provide energy only and so the rest of the diet must be balanced for protein, vitamins, and minerals. Oil provides slow release energy so that the mare has energy release sustained throughout day.


Protein is the fundamental building block for foetal development. Even with good quality forage available most mares will need another source of high quality protein. The quality is important as it is the essential amino acids that do most of the work, some protein sources may be high in crude protein but have low levels of Lysine which will hamper foetal development. Lysine is acknowledged as being the primary limiting amino acid in horses and must be readily available in the diet.

Calcium and Phosphorus

These minerals are essential for bone growth and general foetal development. The amount in the diet is important but so too is the ratio. The Ca:P ratio for broodmares should be in the region of 2:1. Products such as 14% Stud Mix or 14% Stud Cubes have ideal Ca:P ratios. Analysis of hay, grass and soil may be helpful in calculating the actual Ca:P ratio intake in pregnant mares if you are suspicious of ongoing problems on a specific farm regarding milk production, birth weights and developmental orthopaedic diseases in weanlings and yearlings.

Vitamins and Minerals

The natural breeding season of mares falls so that mares should foal when the spring grass is at its best, with high levels of Vitamin A and E. Because many of our mares now foal before the grass is rich or have limited access to grass due to stocking rates, it is important to maintain high levels of Vitamin A and E in the diet.

Selenium is often available in supplements for pregnant mares and is an important antioxidant. One study shows improved uptake of colostrum in foals born to mares with high selenium intake rather than restricted selenium diets. Copper too is important for skeletal development of the foetus. Ireland has several pockets of copper deficient soil and so land management and diet must be considered together.

Iodine too is required but in low doses and excesses during pregnancy may cause problems with the foals. Seaweed has a high iodine concentration and should be used very cautiously in the diet of pregnant mares.

Lactation Increases the Mare’s Needs

It is in fact when the foal is born that the mare must work the hardest, the lactating mare has very high nutritional requirements to ensure that she can provide excellent nutrition for her nursing foal. A mare will produce about 3% of her bodyweight in milk daily in the first month of lactation. (A 500kg mare produces about 15l).

Mares in late gestation and lactation will also increase their water intake so ensure that ample water is available.

Improved Rebreeding Efficiency

Mares whose diet meets all their needs will also cycle well post foaling with improved hormone levels and ovulation rates than mares with poor nutrition. These mares also have improved fertility with higher pregnancy rates thus reducing financial losses of having barren years or taking repeated cycles to go back in foal.

The typical 500kg broodmare should be fed a minimum of 3.5kg of 14% Stud Mix or 14% Stud Cubes per day with good quality forage. For specific advice for feeding mares that are under or overweight please contact a member of the Connolly’s RED MILLS nutrition team.

  • Tags:
  • Horses
  • Broodmare
  • Lactation
  • Pregnant Mare