Effect of NDF concentration and physical form of fescue hay on rumen degradability, intake and rumen turn-over of cows

During two experimental periods, eight non-lactating, rumen fistulated Simmental cows were given 2 kg/day of a cereal-based concentrate and fescue hay ad libitum. The hay differed in neutral-detergent fibre concentration (LNDF: low; HNDF: high) and physical form (L: long; C: coarsely chopped). The rumen degradability of the dietary ingradients and of an extracted soya-bean meal was studied using the polyester-bag method. The estimated effective rumen degradability (DG) of dry matter (DM) was significantly higher for LNDF than for HNDF hay (0.490 v. 0.401; P < 0.01). The DM DG of the extracted soya-bean meal and the dietary concentrate were higher when incubated with LNDF than with HNDF diets (0.630 v. 0.581, P < 0.05, and 0.541 v. 0.514, respectively). Chopping the hay significantly increased the daily DM intake for HNDF diets (from 9.9 to 11.6 kg; P < 0.05), while no statistical differences were found between the other diets (10.2 and 9.6 kg, respectively for L-LNDF and C-LNDF diets). Cows given HNDF hay drank less water (42.4 v. 51.7 l/day) and total water consumption, expressed per unit of DM intake, was lower for the HNDF diets (4.1 v. 5.3 l/kg DM; P < 0.01). Dietary treatments did not affect the estimated rumen turn-over rate of hay (0.027 per h on average, k1), hay post-rumen turn-over rate (0.069 per h on average, k2) or the estimated rumen liquid turn-over rate (0.100 per h on average, k). The calculated outflow from the rumen was lower for the HNDF diets (159.4 v. 198.7 l/day). The daily amount of estimated saliva secreted did not differ between treatments, although saliva expressed per kg DM intake was significantly lower for the HNDF diets (10.8 v. 14.8 l/kg DM; P < 0.05). The HNDF diets gave a lower post-feeding rumen pH (6.29 v. 6.58; P < 0.01), a higher concentration of n-butyrate (9.58 v. 8.32 mmol/l; P < 0.05) and a lower concentration of ammonia nitrogen (NH3-N) (80.5 v. 128.5 mg/l; P < 0.05). Of the C4 and C5 iso-acids, the rumen liquid from cows given HNDF diets had significantly lower concentrations of isobutyrate, isovalerate and n-valerate (P < 0.01). Hay physical form did not affect rumen pH, NH3-N and volatile fatty acid concentrations.