Influence of maize grain drying process on its in situ degradability in dairy cows

Rumen degradability of fresh (61% DM - end of wax-ripe stage), freeze dried , and oven dried (at 40 degrees C for 5 d and 60 degrees C for 1 and 3 d) m aize grain was determined by in situ incubation for 0, 2, 4, 8, 12, 16, 24 and 48 h with four nonlactating Holstein-Friesian cows. Oven dried material was degraded at a lower level compared to fresh and freeze dried material. The degradability values of organic matter, starch and crude protein of fr esh and freeze dried grains differed significantly from oven dried grains u ntil an incubation time of 12 h (P<0.01). Correlation coefficients between organic matter and starch degradability, organic matter and crude protein d egradability and starch and crude protein degradability were 0.99, 0.97 and 0.97, respectively. In the early hours of incubation the fresh material sh owed a higher degradability (washing losses up to 19 percentage points) com pared to the freeze dried material. Above 8 h of incubation the freeze drie d material showed slightly higher degradability values. Effective degradabi lity decreased with increasing temperature, especially at high outflow rate s. It can be concluded that it is essential to pay attention to sample prepara tion, which has to be described for comparing results from different degrad ability studies. Besides, the results show that oven drying increases the b ypass of starch.