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Micronutrient Nutrition and the Third Trimester Mare – Part 1: Minerals

by Dr Clair Thunes PhD Nutrition
Consulting Nutritionist for EnviroEquine & PET
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The third trimester is the period of a mare’s pregnancy when the foal is growing the most rapidly. Nutritional requirements for energy, and protein increase gradually from the fifth month with other nutrients needs increasing starting in the second trimester. These increases continue in the third trimester as the growing foal demands greater nutritional support.

Chloride, copper, iodine, iron, sodium, potassium, magnesium, phosphorous and calcium all have an increased requirement for the last trimester.  Most hays are high in iron and potassium and the majority of horses are having their requirements met in excess so adding these nutrients to the diet is typically not necessary.  Similarly if your mare is receiving adequate salt and any alfalfa in the diet the additional sodium, chloride, iodine, magnesium and calcium requirements are also likely being met.

Copper and zinc tend to be low in most forages, and it is not unusual for a typical forage based diet to be deficient in one or both of these.  Additionally the trace mineral profile of the forage is unlikely to be ideally balanced and this can lead to one mineral competing with another for absorption causing deficiencies even though there may be enough of each mineral present in the diet.  Therefore it is a good idea to provide a supplement that will work with the forage to provide additional copper and zinc throughout the pregnancy and improve the ration’s overall mineral balance.  This is particularly important for last trimester mares because copper is required for elastic connective tissue and collagen formation which is the main component of the foal’s developing bone matrix.

While not the only cause of developmental orthopedic diseases (DOD) in foals, there has been research that suggests that foals born to mares that were given supplemental copper had lower incidents of osteochondrosis. Supplementing foals after they were born did not have the same impact. The copper must be received while they are in utero.  It is thought that supplementing the pregnant mare may promote repair of developing osteochondral lesions in the foal.  Therefore it is very important that the mare’s diet provide adequate trace minerals that are correctly balanced to assure absorption and utilization.

Easy keeping mares may need little more than hay and a ration balancer while others will need the addition of a more energy dense broodmare feed.  When fed properly these feeds should insure nutrient needs are met. However, if commercially fortified feeds are being fed at less than the manufacturers recommended intakes this can leave a diet short of essential nutrients such as the trace minerals.  There are numerous supplements on the market containing copper and zinc but many provide insufficient amounts to achieve correct trace mineral balance. A nutritionist can help you determine which commercial feeds and supplements are be best for your mares based on their individual requirements.

The EnviroEquine products GastroBalance, GastroBalance Plus and ElectroBalance all provide supplemental sources of copper and zinc and can be used alone or in combination with your current commercial feed. GastroBalance Plus and ElectroBalance utilize performance minerals from Zinpro®. These versions of copper and zinc are amino acid complexes meaning that the mineral is attached to a single amino acid to aid absorption. In bioavailability trials, Zinpro Performance Minerals continually showed improved bioavailability values in comparison to other sources.

GastroBalance, GastoBalance Plus and ElectroBalance also provide a source of bioavailable silica. Research has shown that mares supplemented with bioavailable silica have higher levels of silica in their milk. Racing Quarter horse foals receiving bioavailable silica have been shown to remain injury free for longer once training and racing. Therefore feeding EnviroEquine products to your broodmare helps to support your foal’s future skeletal health.

Please consult one of our representatives at  [eeb_email email=”” display=”” extra_attrs=”target=’_blank'”] or 1-800-218-1571 to learn how best to incorporate our products into your current broodmare program.

Consulting Nutritionist for EnviroEquine Dr. Clair Thunes is passionate about her profession—one that she decided upon at the age of 14. After earning a Bachelor of Science with Honors from Edinburgh University, and a Master of Science in Animal Science and a PhD in Nutrition from the University of California, Davis, Dr. Thunes went on to found Summit Equine Nutrition LLC an independent consulting company in 2007. An experienced nutritionist and accomplished scientist, Dr. Thunes understands the vital role that nutrition plays in managing horses today. Most importantly, she believes in making nutrition accessible to everyone and removes the guesswork so that owners have the peace of mind that their horse’s diets are optimal for maximum health and peak performance.  Her clients include all horses from competitors at the 2016 Rio Olympics to retired pasture friends, mules and miniature donkeys. She writes a weekly online commentary for and her nutrition articles have been published in noted publications including: The Horse, Equine Wellness, Trail Blazer, Horse & Rider and The Horse Report. Besides consulting she teaches equine nutrition and equine exercise physiology in the Animal Science Department at UC Davis and equine health at Cosumnes River College.  Clair continues to be involved with The United States Pony Clubs, Inc. and she is currently the Regional Supervisor for the Sierra Pacific Region.