The Effect of Variation in Phosphorus Intake on Net Intestinal Phosphorus Absorption, Salivary Phosphorus Secretion and Pathway of Excretion in Sheep Fed Roughage Diets

Abstract

SUMMARYMature sheep fitted with rumen and duodenal cannulae and fed either pelleted hay or grass diets were given supplements of Na2HPO4 by continuous infusion into the rumen and the effects on salivary phosphorus secretion, intestinal phosphorus absorption and pathway of excretion were studied. Little phosphorus was excreted in the urine in control periods and little increase was seen in response to phosphorus supplementation, most of the extra phosphorus given being recovered in the faeces. Infusion of phosphorus into the rumen led to an increase in the flow of phosphorus to the intestine, an increase in absorption, a rise in plasma phosphate level and an increase in salivary phosphorus secretion while withdrawal of supplementary phosphorus was seen to have the opposite effects. In separate studies short sections of the upper small intestine temporarily isolated from the normal flow of digesta were perfused with solutions containing NaH2PO4 (5-50 mmol.1-1). Phosphorus absorption increased with increasing concentration though the relationship was curvilinear such that absorptive efficiency fell from around 0-7 at 5 mmol . 1-1 to around 0-35 at a concentration of 50 mmol. 1-1. The significance of these results in relation to the control of phosphorus balance in ruminants is discussed.

Phosphate Absorption at Different Intestinal Sites in the Developing Lamb

“…Generally greater amounts of phosphate were absorbed from the mid-jejunum in the second compared with the first series of experiments. The greater final phosphate concentration of the perfusate compared to that of the intestinal fluid in the first series of experiments is probably the main reason for this discrepancy, because phosphate absorption is concentration dependent (Scott, McLean & Buchan, 1984a). We have also studied phosphate absorption as affected by the presence of D-glucose or D-galactose 10 mmol/l in the intestinal perfusate.…”

The Effects of Feeding Either Roughage or Concentrate Diets on Salivary Phosphorus Secretion, Net Intestinal Phosphorus Absorption and Urinary Phosphorus Excretion in the Sheep

“…In doing so we have assumed that the difference between the amount ofphosphorus flowing into the duodenum and intake provides a reasonable estimate of the amount of phosphorus added to the digesta via the saliva. As argued previously (Scott, McLean & Buchan, 1984a) we have based this assumption on isolated organ studies in the sheep which suggest that little or no secretion or absorption of phosphorus occurs either in the reticulo-rumen (Scarisbrick & Ewer, 1951;Sperber & Hyden, 1951;Parthasarathy, Garton & Phillipson, 1952), the omasum (Engelhardt & Hauffe, 1975) or the abomasum (Garton, 1951). Further support for these results can be seen in the work of Pfeffer (1968) who added radioactive phosphorus to the rumen contents of sheep fed a pelleted grass diet.…”

Exigências nutricionais de zebuínos: minerais

“…Embora a relação volumoso:concentrado da dieta possa afetar a secreção de saliva (Scott et al, 1984), diretamente ligada à reciclagem de P, nenhum sistema nutricional atesta que as exigências de P variam em função dessa relação. As recomendações são baseadas no consumo de MS total, e não no consumo de volumoso e concentrado separadamente.…”

“…As recomendações são baseadas no consumo de MS total, e não no consumo de volumoso e concentrado separadamente. Apesar de a quantidade de P reciclada via saliva poder apresentar uma magnitude de cerca de 2 a 3 vezes além da quantidade de P ingerida (Scott et al, 1984), o ruminante apresenta uma homeostase muito eficiente do metabolismo desse mineral. Dessa forma, a porcentagem de concentrado em uma dieta por si só não tem efeito pronunciado sobre as exigências líquidas desse elemento para mantença, mas sim para ganho, já que a relação volumoso:concentrado afeta a composição química do ganho.…”