Feeding Horses Chia: Consider Calcium and Phosphorus Balance

Chia is calcium-rich, but inverted calcium-to-phosphorus ratios can cause horses big problems. Here’s what to know.

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Feeding Horses Chia
Chia is calcium-rich, but inverted calcium-to-phosphorus ratios can cause horses big problems. | Photo: iStock
Q: I started adding chia seeds to my own diet recently for the nutritional benefits and am having good results. I want to add it to my horse’s diet too, but I haven’t found a lot of scientific articles about feeding chia to horses. I read your article comparing flax and chia, which I loved. My question: Do you need to balance the calcium-to-phosphorus ratio to make up for chia’s high calcium content? Right now I feed a stabilized ground flax seed supplement that’s fortified to have the correct calcium-to-phosphorus ratio and about 1 pound of timothy pellets, and my horse is on all-day turnout in good grass with access to a trace mineral block in the run-in shed.–Alyssa

A: According to the USDA Food Composition Database, dried chia seeds contain 177 mg of calcium and 265 mg of phosphorus per 28 grams. So, indeed, they have what we call an inverted calcium phosphorus ratio (they contain more phosphorus than calcium). You are correct that this ratio is important when feeding horses. Ideally we want a horse’s ration to contain a ratio of between 1.5 to 2 times more calcium than phosphorus. Should the ration become inverted the National Research Council (2007) states that calcium absorption might be impaired. Even in the face of adequate calcium, excessive phosphorus intake can lead to a condition known as secondary hyperparathyroidism, as well as skeletal abnormalities.

Secondary hyperparathyroidism exists when circulating calcium drops due to low calcium absorption and parathyroid hormone is released resulting in the mobilization of calcium from bones. Chronic demineralization of the facial bones causes a malformation known as “big head.” Hyperparathyroidism was traditionally referred to as big head or bran disease (unfortified bran can have a calcium-phosphorus imbalance, so feeding it can cause the malformation).

Grains such as oats, corn, and barley, as well as grain by-products wheat bran and rice bran, are low in calcium and higher in phosphorus. Traditionally with the reliance on these feeds, bone abnormalities such as big-head were common. Today we feed far fewer grains, and they’re typically incorporated into commercial feeds that have added minerals to correct for such issues and insure a balanced diet. With the popularity of rice bran and flax and the general public’s concerns about inverted calcium phosphorus ratios, feed manufacturers have taken to adding calcium carbonate in order to create a 1:1 calcium-to-phosphorus ratio. Chia being a less well-known feed for horses does not typically have added calcium

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Written by:

Clair Thunes, PhD, is an equine nutritionist who owns Clarity Equine Nutrition, based in Gilbert, Arizona. She works as a consultant with owners/trainers and veterinarians across the United States and globally to take the guesswork out of feeding horses and provides services to select companies. As a nutritionist she works with all equids, from WEG competitors to Miniature donkeys and everything in between. Born in England, she earned her undergraduate degree at Edinburgh University, in Scotland, and her master’s and doctorate in nutrition at the University of California, Davis. Growing up, she competed in a wide array of disciplines and was an active member of the U.K. Pony Club. Today, she serves as the district commissioner for the Salt River Pony Club.

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