RUMEN DEGRADABILITY OF CRUDE PROTEIN OF DRIED GRASS AND LUCERNE FORAGE MEASURED BY IN-SACCO INCUBATION AND PREDICTED BY NEAR-INFRARED SPECTROSCOPY

Samples of grass (16) and lucerne (38) were harvested in advancing maturity and growth stages within 1 year from April to October and were used to test the applicability of near infrared reflectance spectroscopy (NIRS) to estimate ruminal degradability of crude protein (CP). CP degradability characteristics were measured with cows using the nylon bag techniques. Changes in the nutrient contents were consistent with vegetation stage in the primary growth of grass and luceme and the first regrowth of luceme. Total degradability a+b was higher in lucerne forage than in grass. The means (+/- SE) for four growth cycles of lucerne up to full bloom stage were 92.5 +/- 4.28, 93.9 +/- 2.05, 94.0 +/- 0.60 and 96.1 +/- 1.41, compared with 90.0 +/- 5.98 and 90.6 +/- 2.52 for grass up to anthesis in two cycles. Effective CP degradability (ED) of both grass and lucerne decreased with increasing maturity. Up to late blooming stage ED values were between 70 and 82% for grass and 80-90% for luceme. In the primary growth samples, linear relationships (P < 0.001) were found between a + b and ED (Y) and the content of CP, crude fibre (CF) and the day of vegetation (X). Up to the end of bloom stage, for ED: R(2) ranged between 0.85 and 0.94 and SE between 0.78 and 2.9; for a + b the respective values were 0.89-0.97 and 0.59-3.2. NIRS was shown to be more universal than CP and CF content in prediction of ED and a + b values of dried forage. Based on a common calibration at five wavelength terms for combined samples of grass and luceme (n = 54), ED and a + b of all samples could be predicted with a mean standard error of 2.59 and 3.27. NIR data accounted for 0.9 and 0.87 of variability in ED and a+b values in all samples of grass and luceme.