Omeprazole Reduces Calcium Digestibility in Thoroughbred Horses

Proton pump inhibitors like omeprazole reduce nutrient digestibility in humans. This study determined the effect of omeprazole on the digestibility of diets containing limestone or marine-derived calcium (BMC) and to assess changes in blood parameters associated with gastric acid production and calcium status in horses. Thoroughbreds were used to evaluate the digestibility of diets containing different calcium sources with or without omeprazole over four 21-d periods. Each 21-d period had a 15-d diet adaptation phase followed by a 6-d collection phase, consisting of a 5-d total fecal collection period and a final day for gastroscopy and blood sampling. Horses were fed the same diet with either 60 g/d BMC or 50 g/d limestone, so the total diet provided ~45 g calcium. Horses on omeprazole were given GastroGard once daily for the final 14 d of each 21-d period, which supplied 3.91 ± 0.17 mg/kg BW/d of omeprazole. On day 21, blood samples were taken and gastric fluid pH was measured 8 hours after omeprazole administration. Omeprazole had a profound effect on gastric fluid pH compared to nontreated horses. Serum gastrin doubled in omeprazole-treated horses compared to nontreated horses. Omeprazole and calcium source did not affect digestibility of phosphorus, magnesium, potassium, sodium, iron, copper, zinc, or manganese but did affect calcium digestibility. Omeprazole reduced apparent calcium digestibility from 52.0% to 41.4% in limestone and from 55.1% to 46.5% in BMC, equaling a 20.3% and 15.6% decrease in calcium digestibility in the limestone and BMC, respectively. Mineral source had a significant effect on calcium digestibility with BMC at 50.8% and limestone at 46.7%.

Joe D. Pagan, Laura Petroski-Rose, Alana Mann, Ashlee Hauss, Omeprazole Reduces Calcium Digestibility in Thoroughbred Horses, Journal of Equine Veterinary Science, Volume 86, 2020, 102851, ISSN 0737-0806, https://doi.org/10.1016/j.jevs.2019.102851.