The influence of type of diet (roughage or concentrate) on the plasma level, renal excretion, and apparent digestibility of calcium and magnesium in resting and exercising horses

Abstract

Summary In an experiment with six ponies, the effects of exercise and type of ration (roughage/concentrate) on the apparent digestibility, concentration in plasma (including the profile prior to feeding), and renal excretion of calcium and magnesium were studied. The ponies were fed twice daily with alfalfa hay or concentrate (15 g dry matter/kg body weight per day) supplemented with minerals; calcium intake was 278 or 312 mg/kg body weight per day for roughage and concentrate diets, respectively. For alfalfa hay and concentrate, the apparent total digestibility of calcium was 48.3 and 14.1%, and prececal digestibility (determined post mortem) 49.8 and 18.9%, respectively. Plasma levels of calcium were significantly different between ration types. They increased after feeding from 3.3 (roughage) and 2.8 mmol/l (concentrate) before feeding to maximal values of 3.7 mmol/12 hours after feeding roughage and 3.2 mmol/16 hours after feeding concentrate. The renal output of calcium after feeding followed the same pattern, total renal excretion amounted to 56% of total intake during roughage feeding and 19% during concentrate feeding. Plasma concentration and renal excretion of calcium were significantly reduced during exercise. The absorption, profile of concentration in plasma after feeding, and renal excretion of magnesium showed differences between diets similar to calcium; however, the concentration of magnesium in plasma was not affected by exercise. The glomerular filtration rate (inulin clearance) was reduced during exercise by 23% (concentrate) or 42% (roughage).