Classification of silages and their intake with concentrates of different types

The aim of this study was to seek an improved understanding of the factors governing the intake by calves of silage as a sole feed and of the effect on silage intake of different types of concentrate fed with silages of different qualities. A large number of research silage analyses were obtained and the possibility of classifying them into groups of similar chemical composition investigated. Classification of a wide range of silages into distinct groups was found to be possible using the multivariate statistical method, cluster analysis. Silages could be classified into four distinct groups on the basis of toluene dry matter, pH, total nitrogen, ammonia nitrogen, acetic acid, propionic acid, butyric acid and lactic acid. Further silages could be easily allocated to these groups provided that they had been analysed for the above eight parameters. Silages with a more limited analysis of oven dry matter, pH, total nitrogen and ammonia nitrogen were not found to have sufficiently detailed analysis for classification into the same groups. Four linked trials were conducted where the intakes of silages of different types fed with different concentrates were investigated. A silage representative of each of the four classification types, namely a low pH, normal, high dry matter and poorly fermented silage, were fed with five different concentrate types: a standard concentrate, the standard concentrate plus bicarbonate, high starch, high fibre and high protein concentrates. Five twelve week old Friesian calves were allocated to each treatment. The type of silage fed significantly affected silage intake. Intake of the high dry matter silage was markedly higher than the rest. When offered any of these silages without a supplement the animals ate significantly more silage than the animals offered this silage plus a concentrate. There were no significant differences in silage intake between concentrate types but there was a trend, however, for the fibre and bicarbonate supplements to produce the lowest substitution rates. The applicability of single variable prediction equations (based on NDF and crude protein) in predicting the intake of the four experimental silages as a sole feed was investigated. Subsequently more complex multi-variable equations (based on fermentation characteristics and energy values) were used to predict the intake of silage as part of a mixed diet. The single variable equation by LaForest et al (1986) based on NDF was found to be as accurate in predicting silage intake as the complex equations by Rook et al (1990) based on fermentation characteristics. This suggests that factors other than fermentation characteristics are important in determining silage intake