Repeated measurements of P retention in ponies fed rations with various Ca:P ratios.

This study addresses the question of whether feeding rations rich in P for a period of up to 42 d induces a positive P balance in adult ponies. Biochemical bone markers and parathyroid hormone (PTH; intact as well as whole PTH) were measured to obtain clues as to the effect of P loading on bone metabolism. The experiment had a Latin square design.

Influence of high phosphorus intake on salivary and plasma concentrations, and urinary phosphorus excretion in mature ponies.

This study addressed the question whether the concentration of phosphorus (P) in saliva of ponies is influenced by P intake. Six ponies were fed a diet high in P (HP treatment), providing 21 g P/day, and a diet low in P (LP treatment), supplying 7 g P/day. The two diets provided approximately 21 g calcium (Ca) and 6 g magnesium (Mg)/day.

The influence of calcium intake on phosphorus digestibility in mature ponies.

Literature data show conflicting results on the effect of feeding high calcium (Ca) levels on phosphorus (P) digestibility in ponies. None of the studies reported involved a dose response as to the effect of Ca intake on apparent P digestibility while keeping P intake constant. Thus, the influence of high dietary Ca level on apparent P digestibility was studied in balance trials by feeding six mature ponies three different Ca levels against a constant P intake.

Increasing magnesium intakes in relation to magnesium absorption in dry cows.

Earlier studies with temporarily isolated rumen of heifers show saturation kinetics of Mg efflux across the rumen wall. Therefore, we hypothesized that high Mg intakes would not further increase the rate of Mg absorption in cows. To test our hypothesis, six ruminally fistulated non-pregnant dry cows were given diets with different Mg concentrations in a 6 x 6 Latin square design.

High intake of magnesium in relation to the ruminal transmural potential difference and magnesium absorption in wethers.

High potassium (K) intakes are known to decrease magnesium (Mg) absorption in ruminants by increasing the transmural potential difference (PDt, serosal side = positive). High Mg intakes are known to increase the amount of Mg absorbed, which may be explained by increasing the ruminal Mg concentration, but an effect on the PDt cannot be excluded. The objective of this study was to determine whether or not Mg intake affects the PDt.