|Waghorn, Garry - AGRESEARCH GRASSLANDS, NZ|
Submitted to: British Society of Animal Science Occasional Publication Series
Publication Type: Abstract Only
Publication Acceptance Date: April 21, 1997
Publication Date: N/A
Technical Abstract: Gas production kinetics may provide useful information for the formulation of dairy rations. However, measurement of kinetics may be sensitive to experimental conditions and techniques. Our objective was to evaluate the effects of the animal donor and its diet on the measurement of gas production kinetics. Four cows in midlactation were used in a balanced 4X4 Latin square design with a 2X2 arrangement of treatments. Diets containing alfalfa or corn silage, each mixed with corn, soybean meal, and minerals to obtain rations with 24 or 32% aNDF (amylase-treated neutral detergent fiber), were fed twice daily during four week periods. Ruminal contents were collected from each cow, blended with chilled buffer to detach bacteria, and used to inoculate flasks containing either alfalfa or corn silage. The in vitro gas production method of Mertens and Weimer was used. Average pH during 12 h post-feeding was determined for each cow, and a second in vitro trial was conducted during each period with the pH of the in vitro system adjusted to reflect that of the donor. Ruminal pHs were different for each donor and diet. Average pH for the standard in vitro method was between 6.46 and 6.56. Average pHs of the in vitro trial that matched that of the donors were 5.89, 5.76, 5.61, and 5.54 for AS32, AS24, CS32, and CS24, respectively. Gas production kinetics differed among feeds and between in vitro system pH. In addition, both cow donor and its diet affected gas production kinetics. It appears that gas production kinetics is the result of the interaction between feeds and the microbial population available for fermentation. Differences between cows and their diets affected the gas production kinetics of corn, soybean meal, and alfalfa and corn silages, and the differences seemed to be associated with ruminal pH.