A comparative study between lignin down regulated alfalfa lines and their respective unmodified controls on the nutritional characteristics of hay

Altering lignin biosynthesis through genetic approaches impacts the digestibility of alfalfa (Medicago sativa L.) in ruminant systems. Field-grown alfalfa lines engineered for reduced caffeic acid 3-O-ethyltransferase (COMT), caffeoyl CoA 3-O-methyltransferase (CCOMT), and their respective non-transformed controls were harvested four times, and samples incubated with or without tannic acid using a DAISYII Incubator and in vitro gas production methods. Lignin content was reduced in transformed lines compared with their non-transformed counterpart (P<0.05). Lignin content was reduced by 13% and 24% in CCOMT and COMT, respectively, compared with the corresponding controls. In vitro gas production measurements of the down-regulated lignin lines increased 6% and 14% gas production at 72h in CCOMT and COMT lines, respectively, compared with their respective controls. These data were consistent with in vitro dry matter digestibility data at 24h, which showed 4% and 16% higher digestibility for CCOMT and COMT, respectively, compared with their respective controls. COMTNULL had lower (P<0.05) dry matter digestibility at all incubation times compared with the other three lines. COMT was superior in dry matter digestibility compared with its non-transformed counterpart (COMTNULL) (P<0.05) but the difference in dry matter digestibility between CCOMT and CCOMTNULL was not significant (P>0.05). The 8h in vitro gas production was higher in COMT than its respective non-transformed control (P<0.001). The two down regulated lines yielded higher gas production at 72h incubation compared with their respective controls (P<0.001). COMT was superior in 72h gas production compared with CCOMT (P<0.001). The extent of gas production was improved in the low lignin lines by the addition of tannic acid, suggesting a potential benefit of combining these traits. The potential benefits of the down-regulated lignin trait in alfalfa and the interactions with tannin compounds in vitro systems need to be validated using animal feeding studies.