Nitrogen partitioning and estimates of degradable intake protein in wilting orchardgrass and bermudagrass hays damaged by simulated rainfall

This study investigated the effects of simulated rainfall on N partitioning and concentrations of degradable (DIP) or undegradable (UIP) intake protein for wilting orchardgrass (Dactylis glomerata L.) and bermudagrass [Cynodon dactylon (L.) Pers.] hays. Orchardgrass forage was wilted to 674, 153, or 41 g kg(-1) of moisture (WET-O, IDEAL-O, and DRY-O, respectively) in the field before applying the simulated rainfall (0, 13, 25, 38, 51, 64, or 76 mm). For WET-O, DIP (g kg(-1) crude protein [CP]) increased cubically (P = 0.020) with simulated rainfall, but the overall range of response was small (653-673 g kg(-1) CP). Estimates of DIP (g kg(-1) CP) for IDEAL-O and DRY-O decreased by 46 and 25 g kg(-1) CP, respectively, between the 0- and 76-mm rainfall increments; for IDEAL-O, these decreases occurred in a linear (P < 0.0001) pattern, whereas quadratic (P = 0.009) and linear (P = 0.029) effects were observed for DRY-O. Bermudagrass forage was field wilted to 761, 400, or 130 g kg(-1) of moisture (WET-B, MID-B, and IDEAL-B, respectively) and evaluated similarly. For WET-B and MID-B, DIP (g kg(-1) CP) was not affected (P > 0.05) by simulated rainfall. In contrast, quartic (P = 0.019) and linear (P = 0.002) effects were observed for IDEAL-B, but these responses were confined primarily to changes between the undamaged (0-mm) control and the initial 13-mm rainfall increment. On a practical basis, concentrations of DIP were, at most, altered only moderately in response to simulated rainfall and relatively little when forages were still too wet to bale.