Effect of lα-hydroxycholecalciferol on calcium and phosphorus metabolism in sheep given high or low calcium diets

Abstract

SUMMARY: The relationship between calcium and phosphorus metabolism in wether sheep given high or low Ca diets, with or without 1α-hydroxycholecalciferol (1α-0H-D₃) has been studied by a mineral balance and radioactive technique.Ca absorption was not related to Ca intake but was stimulated by 1α-OH-D₃. More Ca was absorbed by treated animals from the high Ca diet than from the low diet and all the extra Ca absorbed was retained, increased retention being brought about largely by an increase in the rate of bone accretion.P absorption was increased to approximately the same extent from both diets suggesting that stimulation was due to the 1 α-0H-D₃treatment rather than increased Ca absorption. Whereas the extra P absorbed from the high Ca diet was retained, together with Ca, in bone and soft tissues, that absorbed from the low Ca diet was largely excreted in the urine. It is suggested that this difference in P retention reflects a difference in availability of Ca for retention in bone and P retention was in fact found to be directly related to Ca retention.The roles of secretion of P into the gut, absorption of P from the gut and urinary excretion of P are discussed in relation to P homoeostasis.As absorption of P from the intestine and loss of P to bone, soft tissues and urine increased, so endogenous faecal loss decreased until it reached a value of approximately 35 mg/day per kg body weight when it remained constant. It is suggested that this value may represent the inevitable loss of endogenous P in the faeces from a hay and concentrates diet and that this minimum value may have a bearing on the calculation of P requirements.