Changes in the rumen digesta kinetics of cell walls with maturity and effect of indigestible cell wall pool on the degradation of forages

Abstract

Crossbred male cattle (6) fitted with rumen cannulae in 2 groups were fed on 7 kg of Stylosanthus hamata and mixed grass hay in the ratio of 1 : 1 (SHMGH) along with 1 kg concentrate for 2 years. SHMGH was harvested at 45 d (CG) or 90 d (EG). DM, OM, NDF or ADF digestibility was higher in CG than EG. Rumen kinetics was studied using rumen evacuation technique. Total rumen content in EG was 9% higher than CG. Rumen NDF pool was 6.67 and 7.91 kg/d, respectively, k in CG and EG. Rate of intake (Ki) and digestibility (Kd) were reduced k on CG than EG but contrary was true with true rate of digestion (Kdt). Average increase in indigestible NDF pool was 80 g/d on EG when compared to CG. The degradability of 5 range grasses and 3 range legumes were evaluated in sacco. Lag time of degradation in grasses or legumes was increased by 1/3 and effective degradability (ED) was reduced by 10%, in EG compared to CG. Average decrease in EDDM or EDNDF (%) was 0.4/d. Correlation of ED with NDF pools indicated that the main impact was due to indigestible NDF pool present in the rumen. Buffering capacity of rumen liquor was reduced significantly on EG compared to CG. Any effect of diet on different N fractions and TVFA’s in rumen was cumulative. In conclusion, major hindrance in animal performance due to feeding of mature Stylo and mixed grass hay was related to indigestible NDF pool and decreased buffering capacity in rumen and reduced the effective degradation of forages by 1/3 in rumen.