INSACCO DEGRADATION OF DRY-MATTER AND NITROGEN IN OVEN DRIED AND FRESH TROPICAL GRASSES AND SOME RELATIONSHIPS TO INVITRO DRY-MATTER DIGESTIBILITY

Regrowths of four tropical grasses (Cenchrus ciliaris, Eragrostis superba, Panicum maximum and Setaria anceps) cut at 4, 6, 8, 10, 12, 16, 36 and 40 weeks were studied for dry matter (DM) and nitrogen (N) degradability (disappearance), in oven dried and fresh samples, in nylon bags incubated in the rumen of a steer for 3, 6, 9, 24, 48 and 72-h. There were significant (P < 0.01 ) differences between grasses as DM and N degradabilities declined steadily with increasing age of grass regrowth for all periods of bag incubation. Differences between the grasses were inconsistent over time. However, on average, C. ciliaris ranked highest and E. superba ranked lowest in both DM and N degradability. Between Weeks 4 and 40 of regrowth, DM degradability after 72 h incubation declined from 70.9 to 26.5%, 64.2 to 11.7%, 76.6 to 15.8% and 72.2 to 20.7% while 72 h N degradability declined from 63.8 to 26.1%, 53.8 to 15.6%, 69.4 to 17.9% and 65.6 to 22.2%, respectively for C. ciliaris, E. superba, P. maximum and S. anceps. Dry matter and N degradabilities of oven dried and fresh samples were similar for all bag incubation times. These differences were not significantly (P > 0.05 ) affected by grass species or age of grasses. Dry matter degradability (DMD) after 48 h incubation was more closely correlated (r = 0.976 - 0.978) with in vitro dry matter digestibility (IVDMD) and had the lowest residual standard deviation of prediction than the other incubation times. However, 72 h DMD were similar in value to IVDMD ( 18.7 - 7 1.0% vs. 20.2 - 72.0%). The mean errors in duplicate sample determinations of 72 h DMD, oven dried and fresh samples, and IVDMD (0.93, 1.4 1, respectively. vs. 1.23% units) were also similar.