Lignin Content and Digestibility of Tifton-85 and Coastal Bermudagrass Hay Produced In Georgia: Effects of Drought.

In many research trials, the hybrid Bermudagrass “Tifton 85” consistently produced higher dry matter with improved fiber digestibility than the more common one “Coastal”. However, the reported superior digestibility of Tifton-85 to Coastal has not yet been verified in actual growers’ situation involving large number of samples. It is also unclear whether Tifton-85 would still be able to maintain its higher digestibility than coastal especially during severe to exceptionally/extreme drought. Recent past weather conditions in Georgia granted a unique opportunity to evaluate this. The National Drought Mitigation Center’s U.S. Drought Monitor classified a large majority of Georgia in their extreme to exceptional drought categories during the 2007 growing season and at least in a severe drought category during 2008. These years had been preceded by one year (2006) and succeeded by one year (2009) of relatively little or no prolonged drought stress. In each year of 2006-2009, a substantial number Tifton-85 and Coastal hay samples were submitted (by growers, livestock farms, and forage business entrepreneurs) for forage quality analysis including dNDF48 at the University of Georgia’s Feed and Environmental Water Lab (FEWL). We studied this considerably large and robust database to provide insight into the digestibility of Tifton-85 and Coastal during drought years and years when drought stress was absent or much less pronounced. Tifton-85 seemed to have a trait of lower lignin content than Coastal. However, Tifton-85 could hold its trait of lower lignin content only in drought free years of 2006 and 2009. Whereas the lignin content of Coastal is unaffected by drought in 2007 and 2008, the same for Tifton-85 increased during these two drought years. Despite this, the digestibility of NDF (dNDF48) for Tifton-85 was higher than coastal regardless of drought situation. This demonstrated in a robust and unbiased manner the fact that lignin composition in Tifton-85 is different from that in coastal as claimed by the breeders. Higher dNDF48 for Tifton-85 is attributable to its lower concentrations of ether-linked ferulic acid in lignin than Coastal. Decreased ether bonding in lignin of Tifton-85 results in higher ruminal microbial digestion of this forage.