Polyphenol oxidase (PPO) had been shown to reduce both proteolysis and lipolysis in incubated red clover (Lee et al. 2004). However it has not been determined whether rumen microbes can adapt to utilise PPO protected protein and lipid. This study investigated whether rumen inoculum from cows offered red clover silage resulted in higher levels of proteolysis and lipolysis in red clover (+PPO) and also in red clover with the PPO1 gene silenced (–PPO) (Sullivan and Hatfield, 2006), than rumen inoculum from cows offered grass silage, due to microbial adaptation.