-Ruminant phosphorus excretion and metabolism were studied through a database. Faecal endogenous phosphorus is the main pathway of phosphorus excretion and averages 0.85 of total faecal phosphorus. The remaining 0.15 is unabsorbed dietary phosphorus. Faecal endogenous phosphorus is mainly unabsorbed phosphorus, with saliva being the major source, and is correlated to factors influencing saliva secretion (DM intake, physical dietary characteristics and dietary phosphorus content). Another source of faecal endogenous phosphorus is rumen microbial phosphorus that escaped solubilisation during post-rumen digestion. All factors stimulating microbial growth would increase phosphorus uptake by the rumen microbes and consequently the faecal endogenous phosphorus. Understanding the determinants of faecal endogenous phosphorus flow will help to precise the determination of net phosphorus requirements for maintenance. The role of plasma phosphorus in urinary phosphorus loss is discussed.excretion / phosphorus / quantitative aspect / ruminant

-Phosphorus absorption in ruminants was analysed from a database described in a previous article. For common values of ingested phosphorus (2.5-5.0 g·kg -1 of DM), 0.73 of dietary phosphorus is absorbed. The remaining variability is probably due to phosphorus quality. Phosphorus absorbed from silage, cereal, cereal by-products and hay differs greatly. The current true absorption coefficient used to calculate daily phosphorus supply is a constant value in the current systems and often it underestimates the true absorption resulting in an excess of phosphorus being supplied in the diets. Adjusting the true absorption coefficient values requires better characterisation of the phosphorus supplied by each feedstuff. Dietary influences (phytate phosphorus, crude fibre, etc.) were investigated but trials assessing the ration effect on phosphorus absorption are lacking. Since rumen microbes have specific phosphorus requirements, particularly for cell-wall degradation, the feedstuff phosphorus availability for the rumen ecosystem is discussed.absorption / availability / phosphorus / quantitative aspect

-The present study was aimed at determining rumen phosphorus availability of some feedstuffs assessed with the nylon bag technique: forage (alfalfa), cereals (control-C wheat, formaldehyde treated-FT wheat, barley, corn), cereal by-products (wheat bran, wheat distillers, corn distillers) and meals (C and FT soya bean meals, rapeseed meals and sunflower meals). Rumen phosphorus availability was not uniform amongst the feedstuffs, varying from 33.1% (FT rapeseed meal) to 84.7% (C wheat). Alfalfa phosphorus release kinetics showed high bacterial phosphorus contamination. Technological treatments affected phosphorus content of by-products by either increasing (wheat bran and distillers) or decreasing (corn distillers) after germ extraction from the seed. Formaldehyde treatment decreasing rumen phosphorus availability (from 77.2% vs. 89.4% for wheat to 33.1% vs. 64.4% for the rapeseed meal) may depreciate the phosphorus nutritional value of FT meals. availability / feedstuff / phosphorus / rumenRésumé -Disponibilité ruminale du phosphore de certaines matières premières mesurée à l'aide de la méthode des sachets nylon. Cet article décrit la détermination, par la méthode des sachets nylon, de la disponibilité ruminale du phosphore d'un fourrage (luzerne déshydratée), de céréales (blé, blé tanné, orge, maïs), de sous-produits de céréales (son et drêches de blé, drêches de maïs) et de tourteaux (soja et soja tanné, colza et colza tanné, tournesol et tournesol tanné). La disponibilité ruminale du phosphore est très variable : de 33,1 % (tourteau de colza tanné) à 84,7 % (blé). La cinétique de libération du phosphore de la luzerne indique une importante contamination par le phosphore bactérien. Les traitements technologiques influencent la teneur en phosphore. L'extraction du germe enrichit (son et drêches de blé) ou appauvrit (drêche de maïs) en phosphore les sous-produits par rapport à la céréale. Le tannage au formol, diminuant la disponibilité ruminale du phosphore (de 77,2 % vs. 89,4 %, blé à 33,1 % vs. 64,4 %, tourteau de colza), semble pénaliser la valeur nutritionnelle du phosphore des tourteaux tannés. disponibilité / matière première / phosphore / rumen

No abstract

An in vivo study was carried out to evaluate the effect of a new ionophore (cationomycin) on nitrogen digestion compared with lasalocid. Three diets based on forage were given (a control diet, a "cationomycin" diet, a "lasalocid" diet) to six sheep fitted with rumen duodenal and ileal cannulae over three different periods in a Latin square design experiment. The supply of lasalocid or cationomycin (33 mg kg−1) decreased (P < 0.05) the breakdown of dietary proteins in the rumen and lowered the microbial protein synthesis whatever the microbial marker used (diaminopimelic acid or purine bases). The duodenal and ileal flows of organic matter (OM), ammonia nitrogen (NH3-N), nonammonia nitrogen, and amino acids (AA) were not affected by the ionophore addition. We could not use the AA profile method to estimate the microbial contribution to the duodenal flow of nonammonia nitrogen because of the strong similarities in AA composition of the feed and the rumen microbial sample. The efficiency of microbial synthesis was significantly (P < 0.05) decreased by cationomycin, and tended to decrease with lasalocid. Only lasalocid increased the digestibility of dietary nitrogen in all the digestive tract. Key words: Ionophore, lasalocid, cationomycin, digestion, nitrogen, sheep, rumen