crude protein and starch degradation and evaluation of pea grains for ruminants.

Thirteen pea grain samples from different origins were used to examine the variation in ruminal degradation of crude protein (CP) and starch as well as gas production (GP) kinetics. GP was used to estimate the digestibility of organic matter (dOM), metabolisable energy (ME) and utilisable CP at the duodenum (uCP). Protein fractions were also determined according to the Cornell Net Carbohydrate and Protein System. Degradation of CP and starch from all pea grains in the rumen was almost complete, with a high proportion of the instantly disappearing fraction. The variation in the degradation constants among pea grain variants was high, and degradation of CP and starch showed a significant initial lag phase in the rumen. The mean effective degradation (ED) calculated for a rumen outflow of k = 8%/h of CP (EDCP8) was higher than ED of starch (EDST8), averaging 77.0 and 71.5%, respectively, with low variation among variants. A correlation analysis between GP parameters and degradation constants showed no clear relationship, but the rates of GP and starch degradation were similar. Most of the protein in the pea grains was buffer-soluble with fast and intermediate degradation. Variation in the protein fractions among the pea grain variants was low and not suitable for predicting differences in degradation characteristics. The mean uCP of pea grains was 198 g/kg dry matter (k = 8%/h) and variation was low and consistent with that of GP kinetics and rumen undegradable crude protein values. The estimation of dOM and ME from 24 h GP led to very high values indicating that the existing prediction equations may not be suitable for pea grains as a single feed.