The effect of dietary intake of calcium and phosphorus on the absorption and excretion of phosphorus in chimaera-derived sheep

Abstract

The effect of ratios of calcium to phosphorus in the diet (varying from 0-6 to 3-6) on the absorption and excretion of P was investigated with four sets of 9-month-old chimaera-derived triplets. A pelleted cereal-based diet supplemented to contain 1-5, 3-1 or 6-2 g P/kg D.M. and 3-4 or 5-4 g Ca/kg D.M. was used in a factorial design.The additional Ca in the diet reduced the efficiency of absorption of the P supplements in the diet by 0-18 ± 004.The efficiencies of absorption of total P were very similar within but markedly different between (P < 0001) sets of triplets, the mean values being 0-62, 0-74, 0-82 and 0-84. The fractional absorption of inorganic P alone showed the same ranking and the mean values were 0-47, 0-67, 0-85 and 0-92. These differences between triplets support the view that the individual differences in P metabolism have a genetic basis. The mean absorbability of P in the basic diet (0-77) and in the P supplements (0-73) were similar.The pattern of excretion of absorbed P between the'faecal and urinary route of excretion varied between the sets of triplets; as P intake increased, the additional absorbed P was excreted in faeces by one set, in urine by another and in faeces and urine by two sets .The relative importance of the faecal route was dependent upon the fractional absorption of P secreted into the gut.

II. Quantitative aspects of phosphorus absorptionin ruminants

“…For instance, some minerals, other than phytate, present in the grain could precipitate phosphorus near the absorption sites [34,44,45] explaining the results of the model 12. The question of the efficiency of phytase is important since phytate phosphorus, under the IP6 form, escaping the rumen without degradation might not be hydrolysed further in the digestive tract.…”

“…Diet effect on apparent mineral availability and retention was not taken into account [32], particularly for phosphorus [33], because variations due to the diet are considered as negligible compared to individual animal variations [34]. Improvement of our knowledge of the mineral content of feedstuff [35] and of phosphorus quality [36] is the two keys for improved supplementation [31] and pollution management [37].…”

The effects of feeding diets containing either NaHCO3 or NH4Cl on indices of bone formation and resorption and on mineral balance in the lamb

“…Prior to counting the plasma samples were deproteinized using 10% (w/v) trichloroacetic acid. The proportion of faecal calcium and phosphorus of endogenous origin was determined by the isotope dilution method using the areas under the specific radioactivity time curves for faeces and plasma (Field, Kamphues & Woolliams, 1983). The faecal data were adjusted to allow for the passage of endogenous minerals along the gut (transit time), which was taken to be equal to the interval after dosing to the time of collection of faeces having the highest specific radioactivity.…”

I. A bibliographic database for quantitative analysisof phosphorus flow in ruminants

“…Pure concentrate diets were also given to lambs for the evaluation of various phosphorus sources [51,54], in another study of phosphorus metabolism [55,56], for the determination of the availability of phosphorus in different feedstuffs [38,57], and for studies of phosphorus excretion [45,58] and phosphorus metabolism [59]. In calves, 100%-concentrate diets were used for studying the influence of diet structure on phosphorus excretion [58,60] as well as the phosphorus metabolism [21].…”