The moment you’ve been waiting for has arrived! Your foal has 4 feet on the ground, your mare is letting baby nurse, and your veterinarian has told you both mare and foal are healthy.
Producing high-quality milk for the foal requires a lot from your mare. Lactation puts higher energy demands on a mare’s body than any other stage of her life. 
To keep up with the milk requirements of a growing foal while maintaining her body weight, your mare requires a calorie- and protein-rich diet.
During early lactation, energy requirements are 84% higher and protein requirements are 232% higher. Requirements for key minerals such as calcium and phosphorus also increase.
Mares will consume more feed to match increased nutrient demands. They also use body reserves of calories, protein and minerals to support milk production.
Supplying high-quality forages and additional feeds as needed can minimize loss of body condition during lactation and help maximize milk production. Adequate vitamin and mineral supply is also important for maintaining mare and foal health. 
Milk Production in Horses
The first milk your mare produces after foaling is called colostrum. Colostrum is rich in antibodies that are required by the foal to defend against bacteria and viruses.
Within 12 hours of birth, the mare transitions to making milk with a much different composition than colostrum. By three weeks post-partum, the milk composition becomes fairly stable for the remainder of lactation.
Mares can produce in excess of 3% of their bodyweight in milk per day.  This high lactation volume continues for approximately 3 months at which time production tapers off as her foal starts to eat solid food. 
How Much Milk Does your Mare Produce?
The amount of milk your horse produces can be estimated from her body weight and the day of lactation.
The National Research Council’s Nutrient Requirements of Horses uses the following formula to estimate milk production: 
Milk yield (kg / day) = (0.0274287 x BW) x d0.0953 x e-0.0043d
In this equation, d is the day of lactation and BW is body weight in kilograms (kg).
Using this formula, milk production for a 500 kg / 1100 lb horse at one month is estimated at 16.7 kg (L) per day. This will decrease to 10 kg (L) per day by 6 months of lactation.
For the first 3 months, your mare will produce roughly 3% of her body weight as milk per day. This decreases to 2% of her body weight for the next 3 months.
At 6 months of lactation, the foal is relying less on milk as he or she begins to consume more solid feeds.
Mare Milk Composition
|Saturated Fatty Acids||47% of fat|
|Unsaturated Fatty Acids||53% of fat|
|Vitamin D||4.93 ug/L|
|Vitamin E||1.13 mg/L|
|Vitamin K||17.93 ug/L|
|Calcium||0.05 – 0.135%|
|Phosphorus||0.02 – 0.121%|
|Potassium||0.025 – 0.087%|
|Magnesium||0.003 – 0.012%|
These values represent averages of mare’s milk taken across several studies. An individual mare’s milk volume and composition can be affected by several factors including: 
- Stage of lactation
- Age of mare and number of previous lactations
- Mare’s diet
Feeding Program for Lactating Mares
Designing a feeding program for a lactating mare requires careful attention to total energy content of the diet as well as ensuring balanced vitamin and mineral levels.
As you feed your lactating mare, it is important to maintain her body condition so she can be rebred early or return to performance as soon as possible.
It is also important to provide the nutrients required to produce high-quality milk in large quantities.
Feeds may need to be added to increase fat and protein intake while avoiding excessive dietary starch from grains, which can lead to lower quality milk production.
Our nutritionists can help you formulate a balanced diet for your broodmare that meets all of the nutrient requirements for both mare and foal. Submit your horse’s diet for a free analysis online.
1) Estimate Nutrient Requirements
Mares must produce large volumes of nutritious milk and have significantly higher nutrient requirements than those required for an adult horse at maintenance.
The NRC’s Nutrient Requirements of Horses calculates the macronutrient and micronutrient needs of your mare at different stages of lactation based on her body weight. 
Daily Nutritional Requirements for Lactating Mares
The following chart provides approximate nutrient requirements for a 500 kg (1100 lb) mare at 3 months and 6 months of lactation. These are the minimum amounts required to avoid deficiency and do not necessarily reflect optimal intake levels.
|Nutrient||Amount (3 months)||Amount (6 months)|
|Digestible Energy (Mcal)||31||27|
|Vitamin E (IU)||1,000||1,000|
Protein, energy and amino acid requirements are highest when the volume of milk production is highest. Along with the requirements for macrominerals such as calcium, phosphorus and magnesium, these requirements decrease as milk production decreases.
2) Monitor Body Condition
Body weight is a major factor affecting nutrient requirements during lactation. Your mare’s body weight will be highest towards the end of gestation and will normally drop during early lactation.
- Foaling month of year
- Diet quality
- Body reserves
It is not just weight that is impacted by lactation but also body condition, which assesses fat accumulation.
Body fat reserves can have a significant impact on lactation and future reproductive performance. If your mare’s diet does not supply adequate energy and protein, she will mobilize stored fat to meet the needs of her foal. 
After your mare foals, closely monitor her body condition score (BCS) and observe any changes over time. Adjust your mare’s diet if required to maintain a healthy condition.
The BCS system assigns a score of 1-9, with 1 being extremely emaciated and 9 being obese. For optimal lactation and rebreeding efficiency, broodmares should be kept at a BCS of 5 – 7.
At a score of 5, the back is flat, and ribs are easily felt but not visually distinguishable. The withers round over spinous processes (projections of the spine) and the shoulders and neck blend smoothly into the body. The fat around the tailhead feels a bit spongy.
Effect on Foal Growth
In some research studies, body condition scores of the mare have been found to correlate with foal birth weight. Mares that are obese during gestation are likely to have heavier foals at birth, and vice versa. However, not all studies have shown this relationship. 
Foals that are born heavy are at higher risk of insulin dysregulation, orthopedic disease and