In vitro rabbit cecal digestibility: effect of copper sulfate and oonor age

In vitro cecal digestibilities of high-, mediumand 1ow-fiber substrates (straw, alfalfa mea!, maize) were measured using cecal contents from rabbits of different ages ( 4, 8, 1 O weeks of age, and adult). Dry matter digestibility of maize was lower (P<0.05) with 4 and 8 week-old rabbit cecal fluid than with cecal fluid from older anirnals. This supports the carbohydrate overload of the hindgut theory of enteritis. There were no age differences in the digestibility of either alfalfa meal or straw. The addition of copper sulfate at concentrations of 50, 125, 250 and 500 ppm copper in the media markedly reduced digestibility of straw and alfalfa meal at alllevels, indicating a pronounced sensitivity of cellulolytic organisms to copper. The digestibility of maize was strongly reduced at levels of 125 ppm or more, whereas the inhibition was less at 50 ppm copper. These results are relevant to use of copper sulfate as a feed additive for rabbits. Introduction Rabbit cecal contents can be used as the source of inocula in an in vitro digestibility system, as described by Aderibigbe ~(1992a,b,c,d). The objectives of this experiment were (1) to determine if the in vitro digestibilities of three types of feedstuffs (high, medium and low fiber) were influenced by age of the donor animals, and (2) to determine if the addition of various levels of copper sulfate to the incubation flasks influenced in yitro digesti.bility. Both objectives are relevant to enteric disease in weanling rabbits, which has been suggested to involve carbohydrate overload of the hindgut of weanling rabbits (Cheeke and Patton, 1980). Copper sulfate levels up to 400 ppm in the diet reduce enteritis incidence (Patton ~., 1982). We hypothesize that the fennentative activity of high-starch ingredients such as maize might be lower in the cecum of the weanling rabbit than for older animals, contributing to an increased susceptibility to enteritis. We also hypothesize that copper sulfate, by its antibacterial properties, might reduce cecal fennentati.on. 1235 Proceedings 5th World Rabbit Congress, 25-30 July 1992, Corvallis – USA, 1235-1240.