Effect of sample preparation on ruminal protein degradability of king grass (Pennisetum purpureum sp)

Studies onruminal protein degradability of tropical forages were carried out to assess an adequate procedure for sample preparation. One hundred samples of king grass were taken from a forage area of the Institute of Animal Science (0.5 ha) according to a completely randomized sampling. The fresh forage sind those submitted to different drying methods (sun drying and oven drying at 60 degreesC were incubated in vitro for 48 hr with ruminal liquor and artificial saliva to determine N-NH3 concentration as an indicator of the extension of ruminal protein degradation in a 3(2) factorial arrangement using the surface response methodology. A quadratic polynomial model with a good adjustment (R-2 = 0.99) was obtained with this methodology which allowed to determine that the maximum concentration of N-NH3 (9.29 mg/100 mi) was attained with the fresh forage after 6.58 hr of incubation while with the 60 degreesC oven-dried posture there were lower concentrations. This model allowed the continuous description of the in vitro ruminal degradation process and to dynamically explore the whole research area. The ruminal degradability percentages estimated by this method were: 47.11, 44.35 and 40.33% for fresh, sun and oven dried forages, respectively. the use of fresh forage as an adequate alternative for the estimation of protein degradability in tropical forages is recommended and further studies allowing to confirm this model are suggested.