A plot study was conducted during 2003 and 2004 in Gainesville, FL to evaluate the effect of N fertilization levels and age of regrowth on crude protein (CP) fractions of ‘Tifton 85' bermudagrass (Cynodon spp.). Treatments were the factorial combinations of three N levels (0, 40, and 80 kg ha-1 per 4 wk) and two ages of regrowth (2 and 4 wk). The plots were harvested at a 15-cm stubble height and an ‘in situ' procedure was used to determine the CP fractions. Duplicate samples of each treatment were incubated in one cow for 0, 3, 6, 9, 12, 24, 48, and 72 h. The McDonald model was fitted to the CP disappearance data. The CP fractions were described as A, rapidly degradable; B, potentially degradable; and C, undegradable. There was a linear increase in total CP (130 to 160 g kg-1) with increasing N fertilization rates from 0 to 80 kg N ha-1. Total CP was lower for 4-wk (120 g kg-1) than 2-wk (160 g kg-1) regrowth. There was no effect of increasing N fertilization levels from 0 to 80 kg ha-1 on CP Fraction A, however, a linear increase in Fraction B (330-455 g kg-1) and a decrease in Fraction C (283-208 g kg-1) were observed. There was greater Fraction C in forage harvested at 4 wk (282 g kg-1) than 2 wk (207 g kg-1). Unfertilized or more mature Tifton 85 herbage had the greatest concentrations of undegradable CP.
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