Effect of increasing the proportion of dietary concentrate for dairy cows on the composition of ruminal contents and faeces and physico-chemical characteristics of duodenal digesta

An experiment was conducted with six dairy cows in a twice replicated 3 x 3 Latin square design, to determine the chemical composition of ruminal contents and faeces and physico-chemical characteristics of duodenal digesta including, viscosity, pH, titratable acidity, microbial protein, total protein, starch and cell wall components. The cows were fed ad libitum, long alfalfa hay (CP = 16.6%) and a concentrate (CP = 17%) in the ratios of 79:21, 50:50 or 23:77 and the effect of diet on digest characteristics was determined to establish an association among diet composition, digesta characteristics and feed utilization. Feed intake was highest for cows fed hay and concentrate in equal proportions (20.9 kg d-1) and greater (P < 0.05) than that of cows consuming 77% concentrate (17.2 kg d-1). Increasing the proportion of dietary concentrate from 50 to 77% did not alter the composition of ruminal contents from the cows. However, content of crude protein was lower (P < 0.05) and that of cell wall components was higher (P < 0.05) in cows consuming the 21% concentrate relative to those consuming 50 or 77% concentrate. Increasing the proportion of dietary concentrate resulted in linear increases (P < 0.05) in viscosity of the supernatant from duodenal digesta, dry matter and protein content. However, a linear decrease (P < 0.05) in microbial protein in duodenal digesta was observed. A quadratic increase (P = 0.05) in starch content and linear declines (P < 0.05) in content of cell wall components in duodenal digesta with increasing dietary concentrate was observed. Content of crude protein and cell wall components in faeces was different (P < 0.05) for cows consuming the three levels of concentrate. Results indicate that the proportion of dietary concentrate affects viscosity of duodenal digesta which may be due to the presence of starch and cell wall components of digesta entering the duodenum and these characteristics may affect nutrient absorption from the small intestine.