SMOOTH BROMEGRASS DIGESTIBILITY TESTS - FUNGAL CELLULASE VS INVITRO RUMEN FERMENTATION

Improvement of forage nutritional value is an important objective of many forage grass breeding programs. Both in vitro rumen fermentation and fungal cellulase techniques are widely used to estimate forage digestibility. The objective of this study was to compare in vitro rumen fermentation and fungal-produced cellulase techniques for use in estimating digestibility for smooth bromegrass (Bromus inermis Leyss.) breeding. Eighteen smooth bromegrass genotypes were grown as replicated spaced plants for 2 yr in the field at Arlington, WI. Forage was harvested at the heads-emerged growth stage of 1-yr-old plantings in 1982 and 1985. Duplicate determinations were made for in vitro digestibility of dry matter (IVDMD) and cell wall constituents using rumen fluid from a fistulated cow (Bos taurus) and dry matter using a prepared fungal cellulase solution with a neutral detergent solution pretreatment (NDSPCS). The IVDMD and NDSPCS techniques had a high phenotypic correlation coefficient (r = 0.81, P < 0.01), similar relationships to lingnin concentration and other cell wall constituents, and similar patterns of genotypic and error variation. This study provides no evidence that accuracy or precision should be an issue in deciding between rumen fermentation or NDSPCS techniques for estimating digestibility in a smooth bromegrass breeding program.