In four trials with growing cattle we observed effects of 1,3-butanediol on rumen fermentation end products, blood components, growth rates, feed efficiency, and body composition. Diets A and C contained 80% grain: 20% alfalfa pellets and 40% grain: 60% alfalfa pellets; in diets B and D, 1,3-butanediol replaced 4% of diets A and C. Feeding 4% 1,3-butanediol caused no significant differences in rumen pH, volatile fatty acid ratios, blood glucose, or blood ketones. Cattle fed 4% 1,3-butanediol had rates of gain and feed efficiency equivalent to and often better than cattle fed the same diet without butanediol. Body composition was not affected by feeding 4% 1,3-butanediol. Results indicate 4% 1,3-butanediol can be fed to cattle without adverse physiological effects and may improve performance. When 6% or more 1,3-butanediol was fed, blood ketones were elevated considerably, animals were hyperactive, gained less weight, and feed efficiency was lower.