Protein degradation and ensiling characteristics of red clover and alfalfa wilted under varying levels of shade

Abstract

The conversion of protein nitrogen (PN) to nonprotein nitrogen (NPN) in forages occurs rapidly and extensively during wilting and ensiling. The objectives of this study were to determine whether the amount of time between cutting and ensiling affects protein degradation in red clover (Trifolium pratense L.) and alfalfa (Medicago sativa L.) silage and to document pre- and post-ensiling characteristics of these two species. Forage from the second (24 August 1993), first (27 May 1994), and second (10 July 1995) growth cycles was harvested with hand clippers to a 5-cm stubble height between 09:00 and 10:00 h on each of the three harvest dates. Herbage was allowed to wilt to a targeted dry matter (DM) content of 350 g kg−1 under 0, 30, 73, and 100% shade (wilting treatment) and ensiled in 100-mL polypropylene centrifuge tubes. Time required to reach the desired DM varied each year, with the greatest range in drying times occurring in 1993. Starch was lower and sugar higher in fresh and wilted red clover than in alfalfa. Fresh red clover contained less NPN than alfalfa in 1993 and 1995 (P < 0.05) and similar amounts in 1994 (P > 0.05). Wilting treatment had no effect on NPN in wilted forage in 1994 and 1995, a result of nearly equal wilting times across shade levels. In 1993, however, NPN increased and starch decreased with shade. Within species, further protein hydrolysis during ensiling resulted in similar NPN levels in silage from all wilting treatments in 1993, despite differences in NPN in pre-ensiled wilted forage. Red clover silage consistently contained less NPN than alfalfa. Wilting treatments did not consistently affect sugar and starch concentrations of silage from either species, although there was a tendency for sugar and starch to decrease with longer wilting periods. Key words: alfalfa, red clover, protein degradation, ensiling