Technical note: forage in vitro dry matter digestibility as influenced by fiber source in the donor cow diet

Objectives of this study were to determine the influence of five donor cow diets that differed in source of fiber on true in vitro DM digestibility of eight forages. Test forages included two alfalfa (31.2 and 38.3% NDF), corn silage (50.2% NDF), oat forage (48.2% NDF), perennial rye (62.1% NDF), two reed canarygrasses (55.9 and 68.1% NDF), and timothy (68.2% NDF). Sources of fiber in donor cow diets were alfalfa haylage or alfalfa haylage plus either corn cobs, cottonseed hulls, oat hulls, or soy hulls. In addition, the effect of filtering through sintered glass crucibles or filter paper (two replicates each) was evaluated. There were differences (P < .01) among feeds in in vitro DM digestibility, but there were no interactions (P > .05) between test forages and either source of fiber in donor diets or filtration method. There was an interaction between source of fiber in the donor diet and method of filtration (P < .01). Samples inoculated with ruminal fluid from cows fed diets with oat hulls or soy hulls had lower (P < .01) in vitro DM digestibility when filtered on crucibles than on filter paper. Filtration method did not affect (P > .05) in vitro DM digestibility of samples inoculated with ruminal fluid from other diets. The in vitro DM digestibility of samples inoculated with ruminal fluid from cows fed alfalfa haylage was less than the in vitro DM digestibility when other inocula were used. The source of fiber in the donor cow diet and filtration method can affect in vitro DM digestibility, but relative ranking of forages was unaffected by these variables.