Recovery of Indigestible Fiber from Feces of Sheep and Cattle on Forage Diets

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Abstract
The usefulness of indigestible neutral detergent fiber as an internal marker was explored in a study involving 24 forages primarily of tropical and subtropical species. Samples of forages, feces, and orts from digestion trials using two or three sheep or cattle per forage were digested in vitro to determine the recovery of fiber. Samples of eight forages and associated orts and feces were also digested in situ. Six days of incubation were required for fiber disappearance to approach an asymptote. Recovery of fiber in feces did not change appreciably after the first 6 d. Mean fiber recoveries for subtropical forages ranged from 83 to 111% with standard errors from .5 to 5.0. Recovery for immature ryegrass forages averaged 130%. Results indicate that although the recovery of fiber among bermuda forages was biased in favor of those having lower fiber content, fiber recovery for sorghum forages was unbiased with a mean of 96% and low standard error (1.5). The hypothesis that bias in fiber recovery is caused by variations in sample particle size is explored.