The effects of grinding, supplementation and incubation period on cellulose digestibility in vitro and its relationship with cellulose and organic matter digestibility in vivo

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Abstract
SUMMARY: The in vitro cellulose digestibility of thirteen cuts of perennial ryegrass, cocksfoot and two varieties of Rhodes grass was determined under different conditions. Cellulose digestibility was increased by increasing the length of the incubation period (1,2 and 6 days), the fineness of grinding of the samples and by addition of a supplement. The effects of fineness of grinding and of supplement were greatest after incubation for 1 day and least after 6 days. Between-run variation in cellulose digestibility was reduced by the supplement and by increasing the length of the incubation period.In a comparison of different methods of predicting in vivo organic matter digestibility the lowest residual standard deviation ( ± 2·29) was with in vitro organic matter digestibility (1 mm screen and incubated with supplement for 2 days). Other residual errors were: in vitro cellulose digestibility ± 2·40, pepsin-soluble organic matter ± 4·93, total available carbohydrate ± 6·39, cellulose ± 6·40 and nitrogen ± 6·46.