FACTORS AFFECTING THE DEAMINATION OF FORAGE PROTEINS BY RUMINAL MICROORGANISMS

Our objectives were to compare ammonia accumulations for fresh alfalfa (Medicago sativa, L.) and birdsfoot trefoil (Lotus corniculatus, L.) at 20, 30 and 40 d of regrowth, and relate these acumulations to the r ates of carbohydrate and protein fermentation by mixed ruminal bacteri a in vitro. Soluble protein as a percent of crude protein (CP) was sim ilar for alfalfa (38.1 +/- 5.9) and trefoil (41.9 +/- 7.1) at 20 d The CP and soluble protein content of both forages declined with age, but the decline was greater for trefoil than alfalfa. At 40 d, the solubl e protein content of alfalfa (as percent of CP) was nearly twice as hi gh as trefoil (19.7 +/- 2.3 versus 11.0 +/- 0.2, respectively). In vit ro ammonia accumulations were higher for alfalfa than trefoil at all s tages. In vitro ruminal nitrogen losses (as a percent of CP) for trefo il declined with maturity (15.3 +/- 1.8% at 20 d vs. 7.4 +/- 0.8% at 4 0 d), but there was little change in N losses as the alfalfa matured ( 15.4 +/- 1. 0%). There was a strong negative correlation between the s oluble carbohydrate content of the forages and N loss (r = 0.78 and 0. 80 for alfalfa and trefoil, respectively), but soluble carbohydrate fe rmentation alone could not explain the differences between alfalfa and trefoil. Trefoil had as much as 4.4% tannin at 40 d maturity, but the alfalfa had little, if any, tannin. Based on the observation that N l oss was greater for alfalfa than trefoil, it appeared that tannis were decreasing protein deamination.