|Waghorn, Garry - AG RESEARCH GRASSLANDS-NZ|
Submitted to: Journal Dairy Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: July 31, 1998
Publication Date: N/A
Technical Abstract: Digestion kinetics may provide information that is useful in formulating rations. The objective of this project was to evaluate the effects of the animal and its diet on in situ digestion kinetics of dry matter and fiber. Four dairy cows in midlactation were used in a balanced 4X4 Latin square design with 2 fiber sources and 2 fiber levels. Diets containing alfalfa or rcorn silage with either 24 or 32% aNDF (amylase-treated NDF) were fed twic daily during four week periods. Alfalfa silage, corn silage, cotton fiber, corn grain, and soybean meal were incubated in situ for 0, 3, 5, 9, 15, 24, 30, 36, 48, 72, or 96 h. Forages were coarsely ground and incubated in large dacron bags. Concentrates were ground and incubated in small bags. Bags were inserted after the morning feeding and incubated during the last week of each period. Bags were rinsed after removal from the rumen, frozen, and mechanically washed before drying at 55 deg C. Bags were extracted in neutral detergent to determine aNDF residues. Blank bags were used to correct for DM and aNDF that infiltrated bags during ruminal fermentation. Kinetics were determined using both logarithmic transformation and nonlinear least squares regression. Ruminal pH 3 h post-feeding varied among cows and diets. In situ digestion kinetics of DM and NDF differed among substrates and were affected by both cow and diet. Differences in digestion kinetics were smaller for concentrates compared to forages. Indigestible matter in substrates differed among cows and diets. In general, the level of NDF in the diet influenced digestion kinetics more than forage source. Both intrinsic feed properties and the ruminal environment affect in situ digestion kinetics. Quantitative relationships are needed before practical use of digestion kinetics can be achieved.