The effect of phenological stage and season on nutritive value, chemical composition and nutrient digestibility of lucerne (Medicago sativa L.) green forage in the alimentary tract of cattle

Green forage of fourteen lucerne varieties grown at four Experimental Stations of the Research Centre for Cultivar Testing in Słupia Wielka was harvested in these stages: the first growth in the budding stage (cut I), re-growths in the pre-bloom stage of maturity (cut II) 35 days after the first cut, and the next cut, 42 days later (cut III). Three bulls equipped with rumen and duodenal cannulas were used to study rumen degradability by the nylon bag technique and intestinal digestibility by the mobile bag method. The nutritive value of lucerne green forage was estimated according to IZ-INRA (2001) feed evaluation system. The composition of the lucerne cuts differed in DM content (P < 0.01); the highest was found in cut III (226.9 g/kg), the lowest in cut II (182.0 g/kg).The crude protein content (CP) in DM of cuts I and II was similar (P > 0.05) but lower in cut III (P < 0.05). Cut II contained the highest (P < 0.05) levels of crude fibre, neutral detergent fibre (NDF), acid detergent fibre (ADF), cellulose (CE), and acid detergent lignin (ADL), and the lowest of non-structural carbohydrates (NFC) and soluble in neutral detergent cell content (CC), (P < 0.01). The differences between cut I and III in the contents of these components were not significant (P > 0.05). The highest DM digestibility in the total alimentary tract was found for cut I (P < 0.05). The DM of cuts II and III was digested at a similar rate (P > 0.05). There were no significant differences between the cuts in effective degradability, digestibility in the small intestine of the fraction not digested in the forestomachs and total digestibility of CP, CF, NDF, ADF, hemicellulose and cellulose (P > 0.05). The digestion of rumen undegraded CP in the post-rumen part of the alimentary tract was lower compared with the digestion of essential amino acids (81% and 98%; respectively). The first cut harvested in the spring in the budding stage contained about 5% more PDIA and PDIN, but 7% less LFU compared with both cuts of regrowth (cuts II and III) which contained on average: 58 g PDIA; 123 g PDIN and 0.93 kg LFU. All the cuts contained similar levels of PDIE, UFL per kg of DM (106 and 0.76 g, respectively).