Excretion of Phosphorus and Acid in the Urine of Sheep and Calves Fed Either Roughage or Concentrate Diets

Abstract

Sheep and calves fed a roughage diet (53% straw+other components) excreted an alkaline urine poor in phosphate whereas when they were fed concentrate diets (80% barley+ other components) the urine was acid and contained large amounts of phosphate of which a high proportion were present as titratable H2PO4. These differences in phosphorus excretion were not related to differences in phosphorus intake nor did they appear to be directly related to acid excretion. Over a wide range in the amount of phosphate filtered at the glomerulus the amount reabsorbed by the renal tubule was consistently less in animals fed the concentrate diets. These differences in tubular reabsorption appeared to be related to differences between diets in the amounts of phosphorus absorbed from the gut but there were no differences between diets in the level of parathyroid hormone in blood.Both sheep and calves fed a concentrate diet composed of barley and fish meal excreted considerably more acid in the urine than when fed a similar diet in which soya bean meal was substituted as the source of protein. Although attempts have been made to account for these affects of diet on acid and phosphorus excretion [Reed et al., 1965;Scott et al., 1971] there is as yet no complete explanation. The experiments described in this paper were designed to examine further renal excretion of acid and phosphate in the urine of sheep and calves fed either roughage or concentrate diets. METHODS Animals and diets. Four castrate Friesian calves and two adult Dorset-Horn ewes were used in these studies. At the beginning of experiments the average weight of calves was 80 kg and of the sheep 53 kg. Both of the sheep and two of the calves (322, 325) were fitted with a rumen cannula (3 cm internal diameter). During experiments the animals were kept in metabolism cages which allowed the separate collection of faeces and urine.Three pelleted diets were used in these studies, a roughage diet and two concentrate 379 diets which are referred to as the soya meal concentrate and fish meal concentrate respectively. These three diets were designed to be about equal in energy and nitrogen content and their composition is given in Table I. Whatever level of feeding was chosen each day's intake was divided into two equal portions, one being given at 09.00 hr and the other at 16.00 hr. Water was freely available at all times. The amounts of food offered in the different experiments are indicated later.

Renal Response to Intravenous Phosphate Infusion in the Sheep

“…There is a high threshold for urinary phosphorus excretion in terms of plasma phosphate levels in these animals (Watson 1933;Hendricks and Seekles 1966) and the kidneys of sheep and cattle appear to be capable of a high rate of phosphate reabsorption (Mayer et at. 1966;Scott 1972;Symonds and Manston 1974) relative to that found in non-ruminant animals (Mudge et at. 1973;Pitts 1974).…”

“…Such factors or the intracellular phosphate levels or both (Mudge et al 1973) may, however, be important in sheep in mediating the renal phosphate excretion responses to grain feeding (Scott 1972) or restriction of salivary phosphorus secretion (Tomas and Somers 1974). These aspects merit further study in order to gain better understanding of the normally high reabsorptive rate, particularly in relation to the regulation of phosphate excretion in sheep.…”

Excreção fracionada do cálcio e fósforo em novilhas nelore antes e durante a gestação

“…O aumento nos valores da mediana da excreção fracionada do P na última coleta devese, em parte, à diminuição das medianas dos valores de P sérico em relação às outras coletas. Os valores da excreção fracionada do P são inferiores aos de Neiger & Hagemoser (1985), que apresentaram mé-dia de 15,6%, obtidos de animais alimentados com concentrados, o que, segundo Scott (1972), aumenta a excreção do P na urina.…”

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

“…Calves were fed a low-phosphorus diet (0.68 g·day -1 ) to determine its influence on dietary phosphorus and aluminum availability [67]. The highest phosphorus intakes were studied for their influence on phosphorus metabolism and excretion in ewes in the maintenance phase [26,58]. Total faecal phosphorus (PFEC TOT ) represented 0.60 to 0.70 of the daily ingested phosphorus.…”

“…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].…”