Effects of forage type on particle size distribution of ruminal digesta and faeces of non-lactating cows fed high quality forage

Abstract

This experiment was conducted to determine the effects of forage type on particle comminution in the rumen and on the critical particle size (CPS) for escape from the rumen in cattle fed high-quality forages at maintain allowance of NRC. Twelve ruminal fistulated non-lactating Holstein cows were offered one of four forage diets (long alfalfa hay (ALH), chopped alfalfa round bale silage (ALS), long orchard grass hay (OGH), and chopped corn silage (CS) with similar dry matter digestibility using a random block design. Whereas the eating time per unit of dry matter (DM) intake was similar for ALH and OGH, mean particle size (MPS) of the ruminal digesta at 3-h post feeding for ALH was lower than that for OGH, and was similar to those for ALS or CS. The ruminating time per unit NDF intake for OGH was lower than those for other diets. MPS of the ruminal digesta at 24-h post-feeding for OGH was significantly lower than that for CS, and was similar to those for ALH or ALS. From these results, a large proportion of the particle size reduction seemed to occur during rumination for OGH, and a large proportion of the particle size reduction seemed to occur during eating for ALH. The weight percentage of faecal DM retained on the 1-mm screen was 28.0%, 25.2%, 12.6%, and 26.2%, for ALH, ALS, OGH and CS, respectively. The MPS of the faeces in the cows fed was 309, 181, 104 and 514 ìm for ALH, ALS, OGH and CS, respectively. These results indicate that the critical particle size for escape from the reticular-rumen in non-lactating cows appeared to be larger than 1.18 mm and the particle size reduction and the passage of digesta from the rumen seemed to be due to factors intrinsic to the forage.