ÉTUDES SUR LA BIODÉGRADATION DE LA MATIÈRE SÈCHE DES FOURRAGES PAR LES MÉTHODES IN VITRO ET DES SACS DE NYLON

Abstract

Rumen degradation of seven cultivars of timothy and one of bromegrass was studied by the in vitro and the nylon bag techniques. The timothy cultivars were the early maturing Basho, Champ and Toro, the intermediate-maturing Climax, Itasca and Timfor and the late-maturing Bounty. The Saratoga bromegrass was early maturing. All plant material was harvested at two stages of maturity; full head emergence and anthesis. Nitrogen content of forages decreased with advance in maturity, but cell walls (NDF), lignocellulose (ADF) and lignin (ADL) values were not significantly affected. At both stages, bromegrass contained more nitrogen than the timothies. Of all cultivars, Bounty was among those showing the highest values and Saratoga the lowest ones in ADF and ADL. Rumen degradation of dry matter estimated by the nylon bag technique was not different between cultivars; however, differences were detected (P < 0.05) using the in vitro method at anthesis. In vitro dry matter degradation of bromegrass was greater than that of timothy. Among timothy cultivars, Climax was degraded the least. Rumen degradation of all cultivars decreased with advancing maturity of the plant. Of the two techniques, the in vitro method showed more precision than the nylon bag technique and could be used to detect small differences such as those existing between cultivars of the same species. Prediction of rumen degradation of timothy hays from the chemical composition of the plant appeared to follow a curvilinear rather than a linear regression model.