Effect of ADL to aNDF ratio and ryegrass particle length on chewing, ruminal fermentation, and in situ degradability in goats

An experiment was conducted to evaluate the effect of the ratio of acid detergent lignin to neutral detergent fiber (ADL/aNDF) and the particle length of ryegrass on chewing activity, ruminal fermentation, and in situ degradability in goats. Four rumen-fistulated goats were fed ryegrass as the sole forage source in a 4×4 Latin square study. The forage was harvested at early or full bloom to result in a low or high ADL/aNDF ratio, and chopped to result in 20 or 5 mm theoretical particle length in each case. Four diets were formed from the combination of these variables, all containing the same forage aNDF concentration. Dietary physically effective neutral detergent fiber was determined using the Penn State Particle Separator with three sieves (1.18, 8.00, and 19.00 mm). Increasing ryegrass particle length increased physically effective neutral detergent fiber of the residue covered on the 8.00 and 19.00 mm screens for the diets and chewing and rumination time, but decreased dry matter intake (P<0.05). Increasing ADL/aNDF and particle length of ryegrass both increased mean ruminal pH, and decreased the duration that ruminal pH was below 6.0 and the concentration of ruminal volatile fatty acids (P<0.05). Low dietary ADL/aNDF increased ryegrass dry matter and aNDF degradation (P<0.01). Increasing ADL/aNDF and the length of ryegrass increases chewing activity and stabilizes ruminal pH, but may reduce dry matter intake, ruminal volatile fatty acid production, and diet digestibility in goats.