Understanding Horse Nutrition, Part 5: Broodmares and Babies, Oh My

Written By Dr. Kris Hiney

Over the last few months we have been discussing exactly how many calories (or megacals for those who are paying attention!) your horse needs to consume, depending on what activities he performs, his personality and what the weather might be doing.

Broodmares and babies.

We have yet to discuss an entirely different class of horses, the broodmares and babies. With the breeding season approaching, it is probably appropriate to talk about this special class of horses’ nutritional needs. While this article will focus on their energy requirements, remember, it is especially key for mom and baby to receive the correct amino acids, vitamins and minerals in the diet. These important nutrients are vital for proper growth and development, and ultimately the longevity or usefulness of your new arrival.

Megacals for Mom - before baby is born.

Let’s start with our expecting momma. Her energy requirements during her early pregnancy are not actually that much higher than a lightly worked horse. (Refer to Table 1 – ENERGY REQUIREMENTS FOR WORK). She should already be in good body condition if you have done your job of preparing your mare for her upcoming pregnancy (See Part 1 of this series, TOO FAT, TOO THIN, OR JUST RIGHT).

If you haven’t (shame on you) your goal is to get your mare to a BCS of at least 5 by the time she is at her ninth month of gestation (See CALORIES, KILOCALORIES, MEGACALORIES – HOW MUCH DOES YOUR HORSE NEED? for more information on increasing your horse’s body condition score). Otherwise, you want to ensure that your mare maintains that healthy BCS of around 5.5 -6.

Essentially the mare in early and mid gestation has lower energy requirements than a horse in light work, making her fairly easy to feed. You can usually support her increased energy needs by simply increasing the quantity of good quality hay. However, during the last trimester of pregnancy, her fetus is growing rapidly, which drives up her energy requirements to fall between horses in light and moderate work.

Table 4. Energy Requirements (Mcal/d) for Pregnant and Lactating Mares. 
Activity Time – tracking weight increase.

If you like being a very hands on horse owner (again – great youth project!), you can also track your mare’s increase in weight that is healthy for her and her foal. Using your weight tape (or string), check your mare’s increase in weight over her pregnancy. Overall, she should gain between 12-14% of her non-pregnant weight. She should gain around 5, 7, 10 and 13% of her original weight in her 8th, 9th, 10th and 11th month of gestation respectively. See Table 5 for a handy reference.

Table 5. The Expected Weight of Mares During Late Gestation by Month Compared to the Mare's Original Non-pregnant Weight. 
Megacals for Mom - after baby arrives!

But look what happens after baby arrives! The new momma actually has quite the job to do in producing milk for her rapidly growing offspring. Her energy requirements have now increased by over 50% of what she needed during gestation. Compared to our working horses, your mare now almost reaches the energy needs of a racehorse of the similar size! Many horsemen often forget how demanding a job milk production truly is for your broodmare. Typically it is most effective to supplement your mare’s diet with a concentrate that is already specifically formulated for broodmares. Consult your local equine feed store or horse nutritionist for advice. This will allow her to meet her increased needs for other nutrients as well. While the broodmare definitely needs the extra calories, it is equally important that the diet is balanced to meet her protein, mineral and vitamin requirements to support lactation, and thus foal growth.

Feeding tips.

In order to provide a rough estimate of the amount of feed you will need for your mare, let’s work through a typical feeding strategy for a mare. We will work with a 1000 lb mare for simplicities sake. Now for both health and behavioral reasons, I encourage owners to always feed horses 2% of their horse’s body weight in hay or forage per day. We will actually visit the logic in feeding strategies in an entire article coming soon. For this mare, that means she should be eating 20 lbs of hay per day. I like to feed the pregnant mares and lactating mares a good quality alfalfa hay, in part to help meet their protein needs, as well as an increased need for calcium. Let’s use alfalfa hay which has a caloric density of 0.93 Mcal/lb fed. If we multiply the caloric content of the hay by the lbs eaten we reach her total caloric intake. 0.93 Mcal/lb * 20 lbs = 18.5 Mcal

Comparing our value here with Table 4 above shows us that the mare can consume enough hay to meet her energy needs. She just doesn’t need to consume that many additional calories. However, I would still recommend supplementing her with a ration designed for broodmares. Her energy intake is, of course, dependent on the mare consuming all the hay she is offered. Does she refuse to eat some of her hay and is therefore wasting it? Do you offer her hay free choice? If the hay is of high quality and is palatable to the mare, typically she will volunteer to eat more than 2% of her body weight per day. Also, remember the best indicator of caloric needs of the mare is her BCS. Keep an eye on her condition when changing feed intake.

Feeding when baby is here!

Now let’s compare our girl while pregnant to when she is lactating. Again, we will feed her the same amount of hay, so that she consumes 18.5 Mcal/d. However, during her peak lactation, she is now 10.4 Mcal short! What are our management strategies now? One easy strategy is simply to allow the mare to consume as much forage as she wants. These girls will often increase the amount of hay they eat per day in order to support their lactation demands. However, as mentioned before, we usually supplement these girls with a broodmare concentrate. Let’s use a grain mix with a calorie content of 1.3 Mcal/lb. (I’m using the energy value of a typical commercial feed designed for broodmares). To determine how many lbs of grain we would feed, divide the amount of calories needed by the calorie concentration of the feed. 10.4 Mcal needed/1.3 Mcal lb = 8 lbs of grain Ideally you would split her grain into two equal feedings per day. Now, while this is a fictitious scenario, most alfalfa hays and typical horse feeds will be similar in their caloric content. Read your feed tag for specific information on the feed you select.

Minerals of Note: 

While this month’s article is truly based on the energy needs of our ladies, I would feel remiss to not mention calcium (Ca) and phosphorus (P) when talking about broodmares. It is essential for proper bone development that these two key minerals are not overlooked. Not only do we need to feed adequate amounts of Ca and P, but they must be fed in the proper ratio. Ideally we want to see the ratio of Ca to P in the diet at approximately two parts Ca for every one part P, or 2:1. However, anywhere between 1:1 and 6:1 is acceptable. What you don’t want to see is the amount of Ca to extend beyond 6 parts or for your ratio to become inverted. In that case, you would have more P than you have Ca. Not sure how to figure it out? Let’s assume she is getting 105 g of Ca and 23 g of P from her hay. We would divide the g of Ca by the g of P, or 105/23 = 4.6. The ratio of Ca to P in this scenario is 4.6:1 which is acceptable. However, our girl will be short on P if she is receiving no additional mineral supplement.

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