Repeated measurements of P retention in ponies fed rations with various Ca:P ratios1

Abstract

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. Each feeding period lasted 42 d, and there were 2 balance trials (ECP1 and ECP2) within each feeding period. Each balance trial lasted 10 d (ECP1: d 11 to 21; ECP2: d 33 to 42). Six ponies aged 2.5 to 7 yr were fed a control diet that provided P and Ca according to the requirement (Control diet: 54 mg Ca·kg BW(-1) · d(-1); 36 mg P · kg BW(-1) · d(-1)), a diet high in Ca and P (HCaHP diet: 146 mg Ca · kg BW(-1) · d(-1); 121 mg P · kg BW(-1) · d(-1)), and a diet with a high P level only and Ca fed to the requirement (HP diet: 54 mg Ca · kg BW(-1) · d(-1); 122 mg P · kg BW(-1) · d(-1)). When fed the Control diet, the ponies showed a zero P and Ca balance over the 42-d period. The HCaHP diet resulted in both P and Ca retention (about 2 g Ca and P/d; P < 0.05). Phosphorus retention (about 2 g P/d) alone was observed when ponies were fed the HP diet, but P retention was only different (P < 0.05) from the Control diet in ECP1. The excretion of P in urine was reduced by greater Ca intake (P < 0.05), and Mg absorption was reduced by high P intake (P < 0.05). Plasma P concentration was raised by high P intake. Plasma Ca levels were not affected by dietary treatment. The greater (P < 0.05) P retentions observed for the HCaHP diet during ECP1 and ECP2 and HP diet during ECP1 could not be explained by processes that could have been indicated by the bone markers or PTH values. It was concluded that dietary-P-induced retention of P in ponies does not seem to be associated with altered bone metabolism in this study.

Multi-Generational Drinking of Bottled Low Mineral Water Impairs Bone Quality in Female Rats

“…The skeleton stores calcium and regulates blood calcium levels. Bone phosphorus can adjust the acid-base balance of body fluids and coeffect with calcium to promote bone matrix synthesis and bone mineral deposition [ 30 ]. Magnesium maintains and promotes bone growth [ 31 ].…”

The Effect of Diet Composition on the Digestibility and Fecal Excretion of Phosphorus in Horses: A Potential Risk of P Leaching?

“…Meyer et al [42] reported higher plasma Ca levels for forage fed horses than concentrate fed horses. Some other studies, however, pointed out that the blood Ca concentration does not depend on the Ca intake [48,49]. Regarding all diets, the average blood serum Ca and P concentrations were within the normal ranges used for Finnhorses (https://www.movet.fi/laboratoriokasikirja/).…”

“…The blood phosphorus levels are affected by phosphorus intake [48,49], which may explain why blood levels were highest in the horses whose diets were supplemented with oats. Greiwe-Crandell et al [50] suggested that mares fed an all-forage diet marginal or low in phosphorus may mobilize P from bone.…”