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

Abstract

SUMMARYMature sheep fitted with rumen and duodenal cannulae were fed either a hay or a concentrate diet and the effects on salivary phosphorus secretion, net intestinal phosphorous absorption and pathway for phosphorous excretion were examined. Route of excretion was markedly affected by diet with urine phosphorus levels being much higher and faecal levels lower when the concentrate diet was fed. This difference was not due to differences in phosphorus intake nor could it be related to differences in either plasma phosphorus levels or net intestinal phosphorus absorption. Salivary phosphorus secretion and renal tubular reabsorptive efficiency for phosphorus were, however, both lower when the concentrate diet was fed. The significance of these effects ofdiet in relation to the control ofphosphorus balance in ruminants is discussed.

II. Quantitative aspects of phosphorus absorptionin ruminants

“…The constant true absorption coefficient values advocated [26,28] appear to be too low. However, the remaining variations are probably due to feedstuffs or diets [6,29,30], differences in phosphorus digestive availability [31] and also differences among species and physiological state.…”

“…However, diets containing more than 6.62 g of phosphorus per kg DM are rarely used. In our database, such diets were used in only two trials, one on ewes fed a diet high in calcium and phosphorus [5], and one on sheep fed a 0.88 cereal diet which inhibited saliva production by reducing the chewing activity [6]. Considering only the studies in which the usual, current range of diet phosphorus concentration Fig.…”

Ruminal phosphorus availability from several feedstuffs measured by the nylon bag technique

“…The phosphorus requirement of rumen microbes is greater than that of the host animal [29] and was determined at 3.8 g of phosphorus per kg of digestible organic matter [12]. Phosphorus is mainly provided by saliva, but salivary phosphorus can be low as when high concentrate diets are fed [32], or before the start of chewing. Therefore, microbial requirements not satisfied by the salivary supply should be achieved through dietary phosphorus that may be much lower when FT meals are fed.…”

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

“…On this type of diet phosphorus repletion after nitrogen and phosphorus deficiency was also analysed Quantitative aspects of phosphorus metabolism 257 [18]. In sheep, 100%-forage diets were given in order to determine the availability of phosphorus in forages [38,39], maintenance phosphorus requirements [40,41] and the phosphorus metabolism [29,[42][43][44][45][46][47][48][49]. [50] used 100% chopped hay diet for the determination of net intestinal exchange of ions.…”

“…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].…”