The aim of thiswork was to evaluate the effects of in situ incubation time and particlessize on the estimates of indigestible fractions of dry matter (iDM), neutraldetergent fiber (iNDF), and acid detergent fiber (iADF) in cattle feeds andfeces. Samples of corn grain, wheat bran, corn silage, elephant grass, sugarcane,signal grass hay, corn straw, and feces obtained from cattle fed high and lowconcentrate diets were used. The samples were ground through 1 mm, 2 mm, and3 mm screen sieve and put in 4 × 5 cm non-woven textile bags (20 mg DM/cm²of surface). The samples were divided in three groups, being each group incubatedin the rumen of a crossbred heifer. The incubation procedure was conducted threetimes with the change of groups among animals. The following incubation timeswere used: 0, 12, 24, 48, 72, 96, 120, 144, 168, 192, 216, 240, and 312 hours.The contents of iDM, iNDF, and iADF were evaluated sequentially in each bag.The degradation profiles were interpreted by a non-linear logistic model. Theparticles size did not influence the estimates of iNDF and iADF. However, theparticles size altered the rumen degradation dynamic rates of DM for corn silageand corn grain; of NDF for sugarcane, corn silage, and corn straw; and ADF forsugarcane. For those samples, the particle size has been positively associatedwith the incubation time necessary to estimate the indigestible fraction. Incubationtimes of 240 hours for DM and NDF, and 264 hours for ADF were suggested forobtaining more accurate estimates of indigestible fractions. The use of 2 mmparticle size can increase the precision of estimates.
