In vitro ruminal digestion of anthocyanidin-containing alfalfa transformed with the maize Lc regulatory gene

Abstract

In vitro ruminal digestion was conducted on novel “purple-green” alfalfa forage that accumulated anthocyanidin and proanthocyanidins through the expression of a maize bHLH anthocyanidin regulatory gene (Lc). The Lc-transgenic genotypes were compared with parental (non-transformed, NT) alfalfa in their in vitro ruminal fermentation, dry matter (DM) and N disappearances, and DM degradability. The transgenic genotypes expressed the Lc gene at different levels when grown under high light conditions, resulting in anthocyanidin contents as high as 136 g g-1 DM. Lc genotypes had lower true DM disappearance than NT alfalfa at 0, 4 and 12 h of incubation, but not at 24 or 48 h. Compared with NT, Lc-transgenic genotypes had a lower content of rapidly soluble DM, but a similar content and rate of degradation of the slowly degradable DM fraction, and a similar lag time for digestion. True disappearance of N was lower for Lc- transgenic than NT alfalfa at the initiation of the incubation. The solubility of both DM and N were negatively correlated with the concentration of anthocyanidins measured in the forage. The results indicate that Lc-transformation reduced the initial rate, but not the extent of DM and N digestion of alfalfa in the rumen. These properties could improve the utilization of protein and possibly reduce the risk of bloat in ruminants consuming fresh alfalfa. However, further increasing the amount of anthocyanidins (or proanthocyanidins) produced in the forage may be required to make this a viable strategy for improved protein utilization and bloat prevention. Key words: Alfalfa, anthocyanidins, Lc-transformation, nitrogen, ruminal digestion