Artificial Rumen Investigations. II. Correlations between in Vitro and in Vivo Measures of Digestibility and Chemical Components of Forages

Abstract

Correlation coefficients were calculated using information on in vitro and in vivo digestibilities of 39 samples of tall fescue representing two to four cuttings per year of four genotypes harvested over a 4-yr. period. Correlations between in vitro dry matter digestibility and in vivo dry matter digestibility were highly significant. Correlations on a within-year basis were lower for the tall fescue samples which had been held in storage. Highest correlations were given by the samples harvested in 1960 and used for in vitro trials shortly after being dried and ground. Correlations using the pooled information from all fescue samples revealed a high positive relationship between the in vitro digestibilities and dry matter and cellulose with several measures of in vivo digestibility. The procedure of determining in vitro dry matter digestibility used in this study appears to be as accurate as in vitro cellulose digestibility for estimating the in vivo digestibility of forages. Crude protein content of the forages was positively correlated with both in vitro and in vivo measures of forage digestibility. Intraclass correlations revealed that in vitro digestibility measures were ineffective in predicting in vivo digestibility when only genotypes within a cutting were considered. This would indicate that it is important to consider the variation within the materials under study when in vitro methods are to be used for differentiation of nutritive values of forages. Crude protein content of the forages also showed a very low correlation when considered on a within-cutting basis.