Preliminary study of the changes in rumen bacterial populations from cattle intoxicated with young oak (Quercus pyrenaica) leaves

Intoxication of grazing cattle occurs repeatedly when they consume large amounts of young oak leaves (OL), that are rich in hydrolysable tannins (HT), due to a shortage of other feed resources. The HT are antimicrobial, although some rumen bacteria can resist or degrade them into potentially toxic or harmless metabolites. To study the effect of the administration of HT-rich OL (Quercus pyrenaica) after a severe feed restriction on the rumen bacterial community and monitor the variations in some bacterial groups that are potentially able to resist or metabolize tannins, 3 ruminally cannulated bulls were initially fed grass hay and then subjected to a severe 8-day feed restriction period, before receiving OL for 6 days. Then, the animals were offered again grass hay for 12 more days. Rumen contents were sampled throughout the experiment. Quantitative real-time PCR and terminal restriction fragment length polymorphism (T-RFLP) were used to monitor the bacterial dynamics. Animal 1 was not intoxicated and showed lower relative abundances of Streptococcus bovis initially and after the OL administration than animals 2 and 3, which showed acute signs of intoxication. The genus Prevotella increased its abundance with the OL administration, whereas Selenomonas ruminantium was reduced. The bacterial T-RFLP profile of animal 1 clustered initially separately from the animals 2 and 3 and was less affected by the feed restriction period. These results showed that the effect of the consumption of HT-rich OL after a severe feed restriction is highly variable in cattle and might rely on the individual composition of the microbiota colonizing the rumen.