Correlated responses in forage yield and nutritional value from phenotypicrecurrent selection for reduced fiber concentration in smooth bromegrass

Selection for reduced fiber concentration in forage crops is considered to be an effective approach to improve the voluntary intake potential of forag es. The purpose of this study was to determine the effectiveness of several modifications to phenotypic recurrent selection for reducing neutral deter gent fiber (NDF) concentration and its effect on correlated variables of sm ooth bromegrass (Bromus inermis Leyss). The selection methods were based on differences in the growth stage sampled (vegetative vs heading), the metho d of determining NDF in the laboratory (wet-laboratory vs near-infrared ref lectance spectroscopy), and the method of intercrossing selected individual s tin situ vs replicated polycross). Selection at the vegetative growth sta ge was most effective, probably, due to minimal sampling variation within p lants. Polycrossing generally increased gains due to more effective interpo llination, but increased cycle time by 50%, resulting in similar gains per year for in situ pollination vs polycrossing. Selection for reduced NDF did not generally affect the digestibility of the NDF fraction. Selection for reduced NDF led to reduced forage yield for all selection methods, due part ly to a genetic correlation with NDF and partly to inbreeding depression. T hree potential solutions were proposed to break the apparent association be tween reduced NDF and forage yield: increase effective population size, pra ctice combined selection for both traits, and/or make chance hybrids betwee n genetically divergent low-NDF strains. An empirical assessment will most likely be required to determine the best of these three potential solutions .