Chia is calcium-rich, but inverted calcium-to-phosphorus ratios can cause horses big problems. | Photo: iStock

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