Digestibility of Grasses Treated with Gibberellic Acid

The effect of GA on digestibility of orchard grass and Kentucky 31 fescue was studied in five experiments using sheep as test animals. GA was applied at rates of 12 to 72 gm./acre 1 to 3 weeks prior to harvest of the grasses. The most consistent effect of GA on chemical composition of the grass was a reduction in protein content. Ether extract and soluble carbohydrate contents were not affected by GA application. Crude fiber was increased slightly in two out of five experiments by GA. NFE content was increased in all five experiments although differences were small in three of these. Lignin was increased in one and decreased in two of the three experiments in which it was determined. Digestibility of dry matter tended to be decreased by GA in four out of five experiments. These depressions were less than 5% and in only two cases were they statistically significant. Digestibility of crude fiber, nitrogen free extract, and cellulose tended to be decreased by GA treatment. Ether extract was more digestible in GA treated grass in two out of five experiments. Due to the small changes in digestion coefficients and chemical composition resulting from GA application, there are not clear explanations for the reduction in dry matter digestibility. In cases where dry matter digestibility was significantly reduced there was a reduction in protein and an increase in NFE content.