Impacts of polyphenol oxidase enzyme expression in transgenic alfalfa on in vitro gas production and ruminal degradation of protein, and nitrogen release during ensiling

The loss of protein by plant proteases during ensiling of forage legumes reduces forage quality, causing both lower animal performance and potential by negatively impacting on nitrogen loss to the environment. Polyphenol oxidase (PPO) enzyme catalyzes the oxidation of phenolic compounds to o-quinones, these easily react with amino acids, proteins or other phenols, to form melanin pigments. We evaluated the effect of transgenic alfalfa with expression of walnut PPO transgene and its effect on ruminal degradation of protein, in vitro gas production and N release during fermentation. In Experiment 1, control and PPO-alfalfa were incubated separately or in combination in the presence and absence of corn starch. In Experiment 2, PPO-alfalfa was incubated either alone or in the presence of 50, 100, or 150 mg of corn starch with or without 50 mg of five phenolic substrates (catechol, caffeic acid, l-DOPA, tyrosine, and gallic acid). In Experiment 3, control and PPO-alfalfa were incubated with and without 100 mg starch and with and without catechol. PPO-alfalfa did not differ (P>0.05) from the untransformed control in gas production and net ammonium–N (NH 4 +–N) concentration, or in vitro rumen degradation of protein (IVRDP). When 100 or 150 mg starch was included, PPO-alfalfa produced less (P