Influence of captan on in vitro and in vivo digestibility of forage.

Four trials were conducted to examine the effects of Captan (N-trichloromethylthiotetrahydrophthalimide) on digestibility of forage. In the first trial, alfalfa-brome hay was digested in vitro with Captan added to the hay at levels ranging from 0 to 150 ppm. Digestibilities of alfalfa-brome dry matter, cell walls, acid detergent fiber, cellulose and hemicellulose exhibited a curvilinear response to Captan level. Maximum responses occurred at 75 to 100 ppm of added Captan. In the second trial, addition of 75 ppm of Captan to alfalfa-brome hay resulted in a significant increase in in vitro dry matter digestibility when fresh rumen fluid was used as the inoculum, but had no effect when distilled water or autoclaved rumen fluid was used as the inoculum. The influence of Captan on rate of in vitro digestion was also examined. Addition of 75 ppm of Captan to alfalfa-brome hay resulted in an apparent increase (19.5%) in rate of cell wall digestion. Five Angus steers were used in an experiment with a 5 x 5 Latin-square design conducted to examine the effects of Captan on in vivo digestibility. Captan was added at 0, 75, 150, 300 and 600 ppm of air dry diet. Steers fed Captan gained faster (P less than .05) and had higher (P less than .05) gains per unit of feed. Digestibilities of dry matter, cell walls, acid detergent fiber, cellulose, hemicellulose and protein were higher (P less than .01) for steers fed Captan than for those fed the control diet. There were not significant responses in gain or digestibilities as Captan level increased from 75 to 600 ppm.