Evaluation of the effects of dietary particle fractions on fermentation profile and concentration of microbiota in the rumen of dairy cows fed grass silage-based diets

Abstract

The study evaluated the effects of three different theoretical particle lengths (TPL) of grass silage on the distribution of particle fractions of the diet and the resulting effects on fermentation profile and concentrations of protozoa and mixed bacterial mass in the rumen of three lactating Holstein cows fed total mixed rations (45% grass silage, 5% grass hay and 50% concentrate) ad libitum. Decreasing TPL of grass silage (long, medium, short) reduced particles retained on the 19-mm sieve of the Penn State Particle Separator, while particle fractions from 8 mm to 19 mm and smaller than 8 mm were increased. Different TPL did not affect pH and the concentration of volatile fatty acids in the rumen. However, lowering the TPL from long to medium increased significantly the bicarbonate concentration, acetate proportion and protozoal number in the rumen, whereas the proportion of bacterial protein in ruminal digesta and its amino acid concentration were significantly increased by the short TPL. For the current feeding conditions, it can be concluded that increasing the fraction of particles between 8 and 19 mm and probably even the fraction below 8 mm by decreasing TPL of grass silage do not adversely affect rumen conditions and can be beneficial in terms of optimising concentration and activity of ruminal microbiota in high-yielding dairy cows.

Keywords:

• grass silage
• ruminal fermentation
• particle length
• microbiota
• dairy cow

Acknowledgements

The assistance of Gaby Lai-Dinh in the isolation of mixed bacterial mass and analysis of amino acids is highly appreciated. We thank the staff of the experimental unit of the Institute of Animal Nutrition for their care to the cows and help during sampling, and the staff of research station “Meiereihof” of the University of Hohenheim for their help in the preparation of TMR.