The ratios of degradation characteristics of forages in the rumen of dairy cows: effect of variety and stage of maturity

In situ digestive characteristics of neutral detergent fibre (NDF), non-fibre carbohydrates (NFC) and crude protein (CP) in alfalfa and timothy were determined in the rumen of dairy cows. Two varieties of alfalfa (Pioneer and Beaver) and timothy (Climax and Joliotte) were grown in western Canada and cut at three maturity stages (alfalfa: 1 = early bud, 2 = late bud, 3 = early bloom; timothy: 1 = joint, 2 = pre - bloom head, 3 = full head). Measured ruminal degradation characteristics were soluble fraction (NFC, CP), undegradable fraction (NDF, CP), lag time (NDF) and rate of degradation of the insoluble but degradable fraction (NDF, NFC, CP). All measured characteristics showed large differences between the two forage species (alfalfa vs timothy) and to a lesser extent between the maturity stages and varieties. Mean total rumen available NDF (248.6 vs 282.5 g kg(-1) dry matter (DM)), NFC (200.5 vs 106.1 g kg(-1) DM) and CP (139.7 vs 44.5 g kg(-1) DM) differed (p < 0.01) between alfalfa and timothy. Based on the measured characteristics, degradation ratios were calculated between total rumen available N and carbohydrates (FN/FCHO), soluble N and carbohydrates (SN/SCHO) and rumen available insoluble N and carbohydrates (EN/ECHO). The ratios showed large differences between the two forages species and to a lesser extent between the varieties and stages of maturity. Alfalfa species had significantly higher (p < 0.01) ratios of FN/FCHO (49.8 vs 18.3 g kg(-1)), SN/SCHO (115.0 vs 36.1 g kg(-1)) and EN/ECHO (28.3 vs 12.0 g kg(-1)) than timothy. These results indicate that alfalfa varieties exhibited a superior rumen fermentation ratio (optimum FN/FCHO = 25-33 g N kg(-1) carbohydrates). The results also suggest a potential N loss in alfalfa and N shortage in timothy. Comparing the two varieties of alfalfa, no differences (p > 0.05) were found in the ratios of FN/FCHO and EN/ECHO, but a significant difference (P < 0.05) was found in SN/SCHO (132.3 vs 97.6 g kg(-1)). However, comparing the two varieties of timothy, there were significant differences (p < 0.01) in FN/FCHO (23.8 vs 12.8 g kg(-1)) and EN/ECHO (15.3 vs 8.7 g kg(-1)) ratios but not in SN/SCHO ratio (p > 0.05), indicating large differences between legume and grass. As plant maturity advanced from stage 1 to stage 3, there were no significant changes in all ratios in alfalfa and timothy except the EN/ECHO ratio in timothy (14.3, 13.4 and 8.3 g kg(-1) at stages 1, 2 and 3 respectively). It was concluded that the degradation characteristic ratios were dependent on species, variety and/or stage of maturity. Such ratios could be used to optimise a dairy diet composition with regard to rumen fermentation. (C) 2004 Society of Chemical Industry.