Palatability and digestibility of grasses treated with gibberellic acid
Brown, Ronald Harold
MetadataShow full item record
Experiments were conducted to study the effect of gibberellic acid on palatability and digestibility of two grasses, orchard grass and Kentucky 31 fescue. The GA was applied as a spray, except one granular application, at rates of 18 to 72 gm./A. Sheep were used to test the grass for palatability and digestibility. In addition to proximate analysis of grass, data were obtained on soluble carbohydrate, cellulose and lignin contents. Chemical composition of orchard grass was not affected by GA treatment. The most consistent effect of GA on the chemical composition of fescue was a depression of protein content. Ash content was decreased slightly, but consistently. GA increased crude fiber in two experiments; did not affect it in three. Nitrogen free extract was increased slightly in three of the five tests. Cellulose was increased by GA in the summer and fall of 1960, but not in the spring. Lignin was increased in the spring of that year and decreased in the summer and fall. Ether extract and soluble carbohydrate contents were not consistently affected by GA. In general, chemical changes by GA were less than 5%. Orchard grass palatability was improved by GA. In two out of three trials with Kentucky 31 fescue, consumption of GA treated grass was about 38% less than for the control. Irrigation increased palatability, probably due to a large difference in moisture content of the grass. No chemical differences observed were consistently related to selection of grass by the sheep. Digestibility of dry matter in grass 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 significant. Digestibility of protein, crude fiber, nitrogen free extract and cellulose tended to be decreased and ether extract was made more digestible by GA. Due to the small changes in both digestibility and chemical composition caused by GA no clear-cut explanations could be given for the reduction of digestibility. The effect seems related to a slight protein reduction and in some cases to an increase in crude fiber and cellulose. Although a number of factors which may affect GA response (time after application, growth rate of grass, light intensity, temperature, etc.) have not been studied, it seems unlikely that this growth regulator will exert much effect on the factors controlling digestibility of grass under field conditions. The effect on palatability is more pronounced, but not consistent. The digestibility of fall grown fescue increased with age. This increase probably resulted from accumulation of soluble carbohydrates and decreases in crude fiber, cellulose, and lignin contents in the grass.
- Doctoral Dissertations