Etude de la valeur alimentaire des pailles de céréales traitées ou non à la soude. III. - Influence du niveau d'apport d'aliment concentré

Abstract

The feeding value of NaOH-treated or untreated cereal straws is modified by several factors, particularly the level of concentrate supplementation necessary to meet the animal requirements. To measure this influence, 2 trials were carried out in sheep. In the 1st trial the animals were fed an untreated straw and a treated straw of different origin with a concentrate supply varying from 7.5-30% of the diet. Each straw was given ad lib and then restricted. In the 2nd trial, the animals were fed the same straw, before and after treatment as well as a concentrate supply representing 15-45% of the diet. The 2 roughages were given ad lib in diets with 2 crude protein (CP) contents, 8 and 12%. The composition of all the diets is reported. The voluntary straw intake was steady (untreated straw) or decreased slightly (treated straw) with 15-30% of concentrates. It decreased slightly more when the diet included 30-45% concentrate. The organic matter and crude fiber digestibility increased when the diet contained up to 15% concentrates, then slowly decreased with the untreated straws given in restricted amounts and more rapidly for the treated straws given ad lib. Restriction of the feed intake strongly increased the digestibility of the treated straw in the 1st trial and cancelled the effect of the concentrate included at the level of 15-30% of the diet. Increase in the CP content in the 2nd trial had only a small effect on straw digestibility. In the 2nd trial, the different cell-wall constituents were separated for a better understanding of the mechanisms involved. Starch digestibility was also measured to evaluate possible variations in the digestibility of the concentrate. Changes in pH, VFA [volatile fatty acid] and NH3 concentration in the rumen juice were also measured. The transit time of indigestible particle was measured as well as the feeding and ruminating behavior of the animals. Results were discussed. The negative effect of an increasing proportion of starch in the straw diets fed ab lib on the fermentation rate of cell-wall constituents in the rumen was underlined.