Genetic-Variation In Tall Fescue Digestibility Estimated Using A Prepared Cellulase Solution

Breeding tall fescue (Festuca arundinacea Schreb.) for improved digestibility in the fall is an important goal for improving animal performance. Objectives of this study were to determine the extent and nature of genetic variability for in vitro digestibility and to predict genetic gain from selection. Fifteen parents were randomly chosen from a broad-based population, and their half-sib (HS) families were generated using a polycross mating design. Herbage samples were incubated in a neutral detergent solution (NDS) before being subjected to degradation in a prepared cellulase solution (PCS) to obtain estimates of in vitro digestibility (NDSPCS). Neutral detergent fiber (NDF), acid detergent fiber (ADF), hemicellulose (HEM), and NDSPCS estimates were obtained for parents and their HS families for the summer and fall seasons of 2 yr. Significant (P < 0.01) variation was observed for NDSPCS estimates for HS families and parents in summer and fall, respectively. Genetic variance components for NDSPCS estimates were high among HS families and parents in the summer and fall, respectively. Narrow-sense heritability estimates for NDSPCS were 0.65 in the summer and 0.30 for the fall. Narrow-sense heritability estimates for crude fiber ranged from medium to high, while broad-sense heritability estimates ranged from low to medium. Estimates of broad- and narrow-sense heritabilities were similar for NDSPCS for the summer and fall harvests, because additive genetic variance appeared to be the most important component of the toal genetic variance. The narrow-sense heritability estimated by parent-offspring regression (h(op)2) for NDSPCS was higher for the fall harvest, which suggests that initiation of a breeding program to improve in vitro digestibility in the fall is possible. Predicted genetic gains per cycle of phenotypic selection were 53, 21, and 48% of the population means for the fall harvest for NDSPCS, NDF, and ADF, respectively. Phenotypic selection for improved digestibility in the fall for this population should be possible using the NDSPCS procedure.