Correlated responses in forage yield and nutritional value from phenotypic recurrent 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 forages. The purpose of this study was to determine the effectiveness of several modifications to phenotypic recurrent selection for reducing neutral detergent fiber (NDF) concentration and its effect on correlated variables of smooth bromegrass (Bromus inermis Leyss). The selection methods were based on differences in the growth stage sampled (vegetative vs heading), the method of determining NDF in the laboratory (wet-laboratory vs near-infrared reflectance spectroscopy), and the method of intercrossing selected individuals (in situ vs replicated polycross). Selection at the vegetative growth stage was most effective, probably, due to minimal sampling variation within plants. Polycrossing generally increased gains due to more effective interpollination, 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 partly to a genetic correlation with NDF and partly to inbreeding depression. Three potential solutions were proposed to break the apparent association between reduced NDF and forage yield: increase effective population size, practice combined selection for both traits, and/or make chance hybrids between genetically divergent low-NDF strains. An empirical assessment will most likely be required to determine the best of these three potential solutions. Received: 1 November 1998 / Accepted: 10 April 1999