Y. Naydenova*, V. Kosev

Institute of Forage Crops, 89 Gen. Vladimir Vazov, 5800 Pleven, Bulgaria

Abstract. Compositionanddigestibilityarestudiedandpotentialforagefeedingvalueisestimatedofeightbreedingspringandwinterforms–twoBulgarian and two Russian varieties and their four hybrids, presented as Component A – winter forms and Component B – spring forms. Forage quality is evaluated in three vegetative stages of plants, grown in Competitive variety trial (2011 –2013) on the Second Experimental Field of the Institute of Forage Crops, Pleven: budding stage, beginning of flowering stage and full pod formation stage. The parameters of principal composition (Weende analysis), plant cell walls fiber components content (Van Soest detergent analysis), enzyme in vitro digestibility of dry and organic matter (method Aufrere), potential energy and protein feeding value by different systems are analyzed, determined and estimated. The correlation relations between parameters are established. The highest values forthecrudeproteincontentbreedingformsappearinbuddingstage:CP23.55±7.75% andthehighestaveragedigestibilityinthefullpodformationstage, which is a stage of technological maturity of varieties and hybrids: Digestibility of dry matter (IVDMD) 70.00±3.32% and Digestibility of organic matter (IVOMD 71.28±3.06%). Potential energy feeding value of the forage biomass average for all breeding accessions is the highest at full pod formation stage and protein feeding value – at budding stage. Genetic advance is evaluated by Principal Component Analysis, Cluster analysis and heritability (broad sense) is established.