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-Seventy-nine forages of known in vivo organic matter digestibility (OMD) out of which 45 of known voluntary dry matter intake (DMI) all measured with sheep, were submitted to the in vitro gas production (GP) technique. The aim was to study the prediction accuracy (R 2 , RSD) of the nutritive value of the main components of forages that is, OMD, DMI and voluntary digestible organic matter intake (DOMI). This accuracy was compared with that obtained with the pepsin cellulase method (Cellulase). It appeared necessary to consider the forages by category (grasses or legumes and green forages or hays) in order to obtain a better accuracy in OMD prediction. The "(a + b)" value of the GP model = a + b (1-e -ct ) used to fit the data did not appropriately predict OMD, which was much better predicted from the "c" value (related to the rate of fermentation) or by Cellulase. For grass hays, the OMD was already well predicted by GP 24 h × CP (gas produced after 24 hours × crude protein content). The accuracy of digestibility prediction was improved by adding CP as a complementary variable except with lucerne hays. The relationships between DMI and gas production (at a given time or at the end of fermentation) were fair and not really improved by adding CP content. However, the accuracy of DOMI prediction was slightly better with "c" × CP than with Cellulase for green grasses and grass hays, although Cellulase was better for DOMI prediction of whole lucerne. Although the gas production technique was less efficient than Cellulase to predict OMD it is an interesting technique for predicting voluntary DOMI, that is the global nutritive value of forages. prediction / organic matter digestibility / ingestibility / in vitro gas production / Cellulase / forages / ruminant Résumé -Utilisation de la technique du gaz-test comme outil de prévision de la valeur énergétique des fourrages. L'objectif de cette étude a été de mesurer la précision de la méthode de la production de gaz (GP) in vitro pour prévoir la valeur énergétique des fourrages et de comparer celle-ci à la méthode pepsine-cellulase (Cellulase). Soixante-dix-neuf fourrages dont la digestibilité in vivo de la matière organique (OMD) était connue ont été utilisés comme substrats. Les valeurs des quantités volontairement ingérées (DMI) étaient connues pour 45 des fourrages. Les substrats étaient fermentés dans des seringues avec le fluide ruminal et la production de gaz était relevée 3,6,12,24, 48, 72, 96 heures après inoculation. Il est apparu nécessaire de considérer les fourrages par catégories M. Chenost et al. 350

Summary -Once harvested and stored it is important to optimize the use of poor quality roughages (PQR) by ruminants. This can be done through treatments, that improve the quality of the roughage per se and through appropriate supplementation and feeding techniques, whether the PQR is treated or not. A tremendous amount of work has been done over the last twenty years at both research and development level. This paper recalls the basic principles and the main technologies available for optimizing the digestive use of poor quality roughages. It also discusses and tries to highlight the advantages and drawbacks of transferring them in practice, with particular emphasis on urea treatment and multinutritional blocks. Two main steps should be considered: (a) feeding the microorganisms of the rumen in such a way that the growth and activity of cellulolytic strains are favoured. This is achieved either by a so called catalytic supplementation or by a treatment and (b) feeding the host animal the necessary nutrients that would ensure a satisfactory nutritional status (including its intake capacity which is generally low with such a type of basal diet) to meet its production requirements. Provided some key rules, described in the paper, are observed, the «urea treatment» is technically perfectly adapted to small production units, at both the individual and the cooperative level. Much practical field experience has been acquired now in an extremely wide range of agro-ecological and sociological conditions. Sealing is less a concern than with an anhydrous ammonia treatment and is not necessarily important when large quantities of plant material are treated (self covering). Locally available material such as banana leaves or sheaths, seko mats, banco, mud and old plastic bags proved to be successful on farm scale. Animal response to urea treatment is similar to that observed with anhydrous ammonia treatment achieved at the same alkali level. This response is optimum with moderatly yielding animals (whose diet consists essentially of PQR) making them the «target animals». The «catalytic» supplementation supplies Non Protein Nitrogen (NPN) (namely urea) and minerals (the "strategic" supplements). This supplementation hardly covers the maintenance requirements of the animals. The carrying medium is either liquid, such as the molasses-urea mixtures used in Egypt or solid, in the form of multi nutritional blocks, now used in villages in many countries. Practical examples are given. Thanks to these blocks it is possible to incorporate local agro-industrial by-products that, otherwise, would be under-utilized. The supplementation required for higher levels of production should, at any time: (a) not endanger the cellulolytic rumen ecosystem (this prerequisite is of particular importance with treated roughages for not losing the benefit of the treatment), by providing digestible matter of plant origin (b) supply high quality («by pass», PDIA or undegradable) proteins. Unlike commercial concentrates, it consists of: (a) farm residues ...

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The horse fecal particle size is small but is larger than that of the sheep: I .8 and 0.3 mm, respectively (n : 11). The iize depends on the forage composition and digestibility. The particle lignification is lower in horse than in sheep feces because the cellulosic cell walls are less digested.Key words: Horse, sheep, fecal particle size, fecal particle lignification on a scale from 0 to l0 (Grenet 1970).The results show that the proportion of DM retained on the sieves varied widely according to the diet (Fig. 1). The mean fecal particle size in the horse was small (1.8 -f 0.8 mm) but was, however, higher than sheep particle size (0'3 r-0.08 mm). The correlation coefficients between the percentage of fecal DM retained on the sieves equai to or higher than 0.16 mm and the forage and feces characteristics are given in Table 2