The development of fecal indices for predicting forage intake and quality of forage consumed by lactating beef females allowed an array of forage types

Eighty-six in vivo digestion determinations over 2 years with 3-year old, spring-calving cows were made on fresh red clover, orchardgrass-white clover, fescue, N-fertilized fescue, fescue-red and white clovers-lespedeza, bluegrass, hairy vetch-orchardgrass, bermudagrass and bermudagrass-red and white clovers harvested at various maturities to obtain an array of dry matter digestibility (DMD). Fecal samples were analyzed for proximate anal-ysis, detergent fiber fractions, selected minerals, density, in vitro DM digestibility nucleic acids, digestible NDF, N of fiber fractions, cell solubles- N and AIA. Acid soluble ash, NFE, cellulose, cellulose-N, hemicellulose, hemicellulose-N, indigestible NDF, microbial-N and endogenous-N were calculated. Samples were dry-sieved after grinding through a 1 mm screen and a modulus of fineness for 1 mm, .5 mm, .25 mm screens and smaller than .25 mm particles (MF1MM, MF5MM, MF25MM, MFBOTTOM) calculated. Factor analyses were used to identify redundant variables and linear correlations among inde pendent variables and between dependent and independent variables obtained. Variables related (P<.05) to DM intake (DMI) were; N, ADFN, ADLN, CFN, CELLUN, HEMIN, ADL, CELLU, MF1MM, MF25MM, MFBOTTOM, DENSITY, IVDMD, AIA, Ca, Mg, Na, Mn, DM. Those related (P<.05) to DMD were: N, ADF, NDF, HEMI, CELLU, DEN SITY, IVDMD, AIA, Ca, Mg, P, Cu. Nitrogen, ADFN, ADLN, CELLUN, ADL, NDF, CELLU, MF25MM, MFBOTTOM, IVDMD, AIA, Ca, Mg, Na and Mn were related (P<.05) to digestible DMI (DDMI). N. ADFN, CFN, SOLN, CELLUN, HEMIN, NDF, ADF, ADL, CF, HEMI, MF5MM, MF25MM, MFBOTTOM, DENSITY, IVDMD, ASH, AIA, Ca, Na, P, Mn and Cu were related (P<.05) to fecal DM outout (FDMO). Multiple regression equations were fitted for DMI, DMD, DDMI and FDMO in 3 phases, each succeeding phase more intensive in application. The best models (maximum R²) in phase 1 predicting DMI, DMD, DDMI and FDMO had R² [and residual standard devia-tions (RSD)] of .808 (.92 kg/day). 710 (5.43%), .843 (.79 kg/day) and .882 (.31 kg/day), respectively. The best phase 2 models containing pasture characteristics and fecal variables had R² (and RSD) of .814 (.88 kg/day), .573 (5.75%), .838 (.75 kg/day) and .835 (.32 kg/day) for DMI, DMD, DDMI and FDMO, respectively. Fecal variables added to animal and pasture var-iables yielded R² (and RSD) for phase 3 models predicting DMI, DMD, DDMI and FDMO of .772 (.98 kg/day), .800 (4.33%), .909 (.60 kg/day) and .856 .32 kg/day), respectively. The R² values obtained from these models in-dicate that multivariable fecal indices can adequately predict forage intake and digestibility of extensively grazing beef cows.