The effect of the stage of maturity of alfalfa (Medicago sativa L.) on the chemical composition and in sacco digestibility

The influence of the stage of maturity of alfalfa on the chemical composition and in sacco digestibility was studied in a laboratory experiment. Alfalfa plants were analysed in 8 vegetation stages harvested in regular intervals before the beginning of bud setting until the fall of blossoms. The contents of nitrogenous substances, fat, crude fibre, ADF, NDF, Ca, P, Na, K and Mg were determined in the samples, and using the in sacco method also the organic matter digestibility in the rumen. Further we assessed the energy content and calculated the N−free extractives (BNLV) value. In some stages the chemical changes were monitored in the whole plant. It was discovered that during vegetation there was a statistically significant increase in the crude fibre content and in the ADF and NDF fractions and a reduction in nitrogenous substances. A strong negative correlation was detected between the stage of maturity of alfalfa and content of crude protein and net energy for lactation (r = −0.97 and r = −0.92, respectively). In the individual stages of vegetation the differences in the content of nitrogenous substances, fibre and fat were statistically significant (P < 0.05). The statistically highest content of crude protein (28.97%) was detected in the first stage before bud setting and the lowest (11.97%) in the stage after the fall of blossoms. Later vegetation also had a stronger depressive effect on the content of fat and NEL. The organic matter digestibility (P < 0.05) was the lowest in alfalfa in the last stage of sampling (62.6%) when it reached a mere 85.99% of the digestibility at the beginning of bud setting. The highest organic matter digestibility (72.80%) was detected in a sample of young alfalfa prior to bud setting. In the experiment we confirmed a strong and negative correlation (r = −0.97) between the crude fibre content and organic matter digestibility. The correlation was also strong between the stage of maturity of alfalfa and the content of magnesium (Mg).