Feeding Metabolic Broodmares

If your broodmare is overweight and/or has metabolic problems, her foal could be at risk. Here’s how you can keep both horses safe during pregnancy.
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broodmares grazing in fall
Ensure your mare is a healthy weight before breeding her to decrease the risk to both her and the foal. | Anne M. Eberhardt/The Horse

Q. My Haflinger mare was bred in May and is confirmed in foal. However, since then she has had a laminitic episode. She is stable but, given that she’s in foal, what dietary factors do I need to consider to keep her and the foal healthy?

A. Broodmare nutrition is a critically important management topic for the health of both mare and foal. Pregnancy is a stressor on the body and brings changes in the mare’s nutritional requirements and metabolism. Maintaining a broodmare in optimal body condition and ensuring her nutritional needs are being met is the first step; however, when issues such as laminitis arise, management can quickly become complicated because both the mare and foal are at risk.

Equine Pregnancy and Hyperinsulinemia-associated Laminitis

The body condition of your Haflinger mare is not mentioned, but these horses tend to be easier keepers and are commonly overconditioned. Use caution when breeding a horse that is overweight or has other risk factors associated with the development of hyperinsulinemia-associated laminitis (HAL).

Pregnancy is known to alter the glucose and insulin dynamics of other mammals such as humans and, while this hasn’t been extensively studied in mares, there is some evidence it also happens in this population. Insulin is a hormone that controls the blood glucose (sugar) levels in the body. When a veterinarian diagnoses a horse with insulin resistance (IR), it means the transportation of glucose out of the animal’s bloodstream is less efficient. As the gestational period progresses, there is evidence to support that the body’s insulin sensitivity is decreased.

In a 2011 study, researchers investigated the effects of pregnancy on insulin sensitivity in Thoroughbred mares and found that pregnant mares cleared glucose from the blood more slowly and secreted more insulin than nonpregnant mares. Additionally, in this study, when the Thoroughbred mares consumed a high-starch meal, their glucose and insulin responses were greater than those of the nonpregnant mares, which is evidence of an increased risk of developing laminitis during pregnancy.

Reducing Your Mare’s Risk of HAL

As with most nutritional issues, the best management tactic is prevention, especially in broodmares. Equine nutritionists do not recommend restricting calories to elicit weight loss in a broodmare during pregnancy because it can be detrimental to both mare and foal, so it is crucial your mare maintains a healthy body weight prior to breeding.

Researchers have found an association between obese broodmares and larger foals as well as a higher incidence of delivery complications. For broodmares, veterinarians and nutritionists recommend a body condition of no less than a 5 and no more than a 7 on the 9-point Henneke scoring scale. Additionally, managing other risk factors such as your mare’s sugar and starch intake is important. For the mare that is already well into her gestational period, ensure her diet is balanced and low in starches and sugars.

Equine Nutritional Requirements During Gestation and Lactation

A mare’s nutritional needs change throughout the gestational period and when the mare begins lactating. The National Research Council (NRC) Committee on Nutrient Requirements of Horses states that a pregnant mare begins needing additional nutrition above and beyond her maintenance requirements in the fifth month of gestation. This change begins with increased protein. When the mare reaches the seventh month of gestation, she needs more minerals such as calcium, phosphorus, and magnesium, but the period of peak nutritional requirements is during lactation.

A 500-kg (or 1,100-lb) mare in the seventh month of gestation needs a minimum of 729 g of crude protein in her diet daily. If she is consuming 2% of her body weight in hay (10 kg or 22 lbs) and that hay is 10% crude protein, then it will meet her protein requirement during gestation but not lactation. It is important to test your hay because you might be able to use a ration balancer that provides vitamins and minerals for your mare’s gestational period, but you will need to begin providing additional protein during lactation when the protein requirement increases to over 1,500 g per day.

For your pregnant mare, equine nutritionists recommend that you:

1. Test your hay.

The first step is testing the hay so you are equipped with the information necessary to balance your mare’s diet. For any horse with a history of HAL, it is imperative you know the sugar content of the hay because this information will help you determine if it is safe to consume, needs to be soaked, or if you must source a different type of hay for your mare.

2. Balance the diet.

A balanced diet is imperative to optimally support equine well-being. Meeting broodmares’ nutritional requirements is crucial not only for their health but also their foal’s. Most broodmares that are easy keepers do well on a quality forage with a ration balancer. Since your mare has a history of HAL, many of the maternity feeds are likely too high in starches and sugars for her to safely consume. Choose a ration balancer that is low in nonstructural carbohydrates (NSC) and provides a supplemental source of protein (if required). In complicated cases such as this, work closely with a qualified equine nutritionist.

3. Implement slow feeding.

As previously mentioned, nutritionists do not recommend restricting feed to elicit weight loss in pregnant mares. However, managing easy keepers’ intake can be beneficial. Providing your mare with her hay in a slow feeder or a slow-feed hay net could work well for controlling her intake.

4. Encourage increased movement.

If your mare has recovered from laminitis and is sound, help her move around more when possible. Sometimes this looks like changing the paddock layout to encourage more walking (e.g., having multiple hay feeding locations that the horses travel between), or it could look like an hour hand-walk every evening. There are many possibilities with this, so be creative.

Take-Home Message

Many changes occur in your mare’s body during pregnancy. If you’re managing a broodmare with metabolic problems—notably one with a history of laminitis—you need to be especially aware of her increased risk of developing HAL due to metabolic changes. At this point in her gestation, be sure to test your hay to ensure it is low in starches and sugars (NSC less than 10%), use a quality ration balancer, and seek assistance from a qualified equine nutritionist.


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Written by:

Madeline Boast completed her master’s in Equine Nutrition at the University of Guelph and started an independent nutrition company known as Balanced Bay. She has worked with a variety of equids—from Miniature Ponies to competing Thoroughbreds. Boast designs customized balanced nutrition plans that prioritize equine well-being, both for optimal performance and solving complex nutritional issues and everything between. 

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