Effect of the administration of young oak (Quercus pyrenaica) leaves to cattle on ruminal fermentation

Two experiments were conducted to study the effects of feeding young Pyrenean oak leaves (OLs) to beef cattle on in vitro ruminal fermentation. A total of 12 ruminally cannulated Brown Swiss bulls were divided into experimental groups that were fed different quantities of OLs via the ruminal cannula (on average 0, 2.5, 5.2 and almost 10 kg fresh matter/animal per day; the treatments designated control, L-OL, H-OL and VH-OL, respectively). Batch cultures of rumen microorganisms and the in vitro gas production technique were used to study ruminal fermentation of two substrates (grass hay and OL) incubated with rumen inocula derived from each bull. Results showed not only a dose-dependent negative effect of feeding tannin-containing OL on ruminal fermentation of conventional feeds, such as the grass hay, but also improved fermentation of tannin-containing feeds, such as the OLs, in bulls fed moderate quantities of OLs (i.e., L-OL and H-OL), which suggests adaptation of the rumen microbial population. Detrimental effects of the VH-OL treatment indicate that the high level of tannins in the rumen of bulls on the highest dose of OLs would have exceeded the capacity of the microorganisms to resist or detoxify them.