Digesta characteristics of dorsal, middle and ventral rumen of cows fed with different hay qualities and concentrate levels.

The influence of fibre content of hay (H) and concentrate level (C) on local differences in the composition of ruminal digesta (ratio of solid to fluid digesta, DM, NDF, ADF and ADL content), particle size (MPL), specific gravity (SG) and fermentation (pH and concentrations of SCFA and bicarbonate) have been tested on two ruminally cannulated Friesian cows (520 kg BW) which were fed restricted, using individual cows as experimental units. Digesta samples were collected via cannula from three rumen layers: 5 to 10 cm (top) and 25-35 cm beneath the top of the particle mat (middle) and 5-10 cm above the rumen floor (bottom). For a main plot treatment (H x C), repeated samples were collected at four time intervals (1 h before and 2, 5 and 10 h after morning feeding) on each of two days. From top to bottom rumen the share of solid digesta mass (SM), DM and NDF contents of squeezed digesta fluid (SRF) and concentration of SCFA decreased (P < 0.05); pH and bicarbonate concentration increased (P < 0.05), while DM, NDF, ADF and ADL contents in SM, MPL and SG did not differ. Higher NDF content of hay (from 47-62%) increased SM, fibre fractions in SM, MPL, pH and concentration of bicarbonate in ruminal digesta, especially when 50% concentrate was given, while SG decreased. When the concentrate level was enhanced from 20 to 50%, digesta SM, MPL and the content of DM and NDF in SRF increased, while pH, concentrations of SCFA and acetate decreased when low-fibre hay was given. With longer time after feeding the digesta SM was reduced and fibre content in SM increased. The increase of the fibre content of hay reduced the possible negative effect of high concentrate level on the stratification of ruminal digesta. The decrease of the fibre content of hay promised better conditions for fibre digestion in the rumen when concentrate availability is limited.