The effects of barley vs. barley fibre with or without distiller's solubles on site and extent of nutrient digestion in cattle fed grass-silage-based diet

Abstract

A 4 × 4 Latin square experiment with a 2 × 2 factorial arrangement of treatments was carried out to determine the effects of by-products from integrated starch-ethanol production on the digestion of organic matter (OM), nitrogen (N) and cell wall carbohydrates in cattle fitted with rumen and duodenal cannulae. The diets consisted of 500 g kg −1 dry matter (DM) of a mixture of grass silage and hay (3:1 on DM basis) plus one of four concentrates: barley (BU), barley + wet distiller's solubles (WDS) (BD), barley fibre (FU) and barley fibre + WDS (FD). WDS comprised 150 g kg −1 of the total DM. The mean amount of DM given was 6.7 kg day −1. The amounts of OM entering the duodenum and voided in faeces were higher ( P < 0.001) with F diets than with B diets, and thus both rumen and total OM digestibility were lower ( P < 0.001) for F diets. Inclusion of WDS in the diet improved ( P < 0.001) rumen but not total OM digestibility. Because barley fibre has a higher fat content than has barley, the difference in digestible energy content between the diets was smaller than the difference in digestible OM content. Non-ammonia N (NAN) flow at the duodenum was higher ( P < 0.05) with F diets than with B diets, and was not increased by increasing dietary N content with WDS. The amount of microbial N entering the small intestine was greater ( P < 0.05) with B diets, whereas estimated feed N flow was higher ( P < 0.01) with F diets. The efficiency of microbial N synthesis increased ( P < 0.001) when F diets were fed and was decreased ( P < 0.01) by inclusion of WDS. The differences between B and F diets in their effects on the total digestibility of cell wall carbohydrates were small. The cattle fed F diets had higher rumen pH values ( P < 0.05) and molar proportions of propionate ( P < 0.001), and lower concentrations of total volatile fatty acids ( P < 0.05) and molar proportions of butyrate ( P < 0.001) than those fed B diets. Feeding WDS in the diet increased rumen ammonia concentration ( P < 0.01) and molar proportions of propionate ( P < 0.001) and butyrate ( P < 0.05) and decreased ( P < 0.001) that of acetate. Rumen protozoal number was lower ( P < 0.001) in cattle fed F diets than in those fed B diets. It is concluded that replacement of barley with barley fibre in the diet resulted in large changes in the digestion of dietary components and in rumen fermentation, and that duodenal NAN flow was not increased by including WDS in the diet.