Comparative Forage Evaluation Using Infrared Reflectance Spectroscopy, Microbial, Enzymatic and Chemical Analyses.

Abstract

A 6 x 6 Latin Square design intake and in vivo digestion trial was conducted using six crossbred steers to evaluate the nutritive value of alfalfa, mature ryegrass, common and Alicia bermudagrass, Pensacola bahiagrass and a 50:50 mixture of alfalfa and ryegrass hays. Voluntary dry matter intake (DMI) and in vivo dry matter digestibility (DMD) ranked the hays in the same order of quality. Alfalfa hay and mature ryegrass had the highest and lowest quality, respectively. The quality of warm season grasses decreased as the length of regrowth period after cutting increased. In vitro dry matter disappearance (IVDMD) increased with increased dilution of ruminal fluid regardless of the donor source of ruminal fluid inoculum or hay substrate. In vitro dry matter disappearance for all hays increased as the length of incubation time increased. Alfalfa hay, which had the highest IVDMD, showed the least increase in IVDMD from 48 to 96 hr. All in vitro ruminal procedures significantly predicted DMD. The Moore procedure with phosphate buffer and the Mellenberger procedure had the highest and lowest coefficient of determination in predicting DMD, r('2) = .88 and r('2) = .72, respectively. Enzymatic procedures also significantly predicted DMD, although they had a wider range than the ruminal procedures. Pepsin-T. viride cellulase + A. niger hemicellulase and pepsin-Onozuka cellulase preparation had the highest and lowest coefficient of determination in predicting DMD, r('2) = .88 and r('2) = .69, respectively. Dry matter intake and digestibility were both significantly predicted by crude protein (CP) and IVDMD. The best predictors for DMI and DMD were CP and IVDMD, respectively. Acid detergent fiber (ADF) significantly predicted DMD, but neutral detergent fiber (NDF) failed to significantly predict DMI. Near infrared reflectance (NIR) (log 1/R) spectra positively identified differences in digestibility between alfalfa and mature ryegrass and between bahiagrass and mature ryegrass. Near infrared reflectance spectroscopy predicted in vivo data with highest accuracy for DMI (r('2) = .84) and lowest accuracy for DMD (r('2) = .75). Prediction by NIR of laboratory analysis was highest for NDF (r('2) = .98) and lowest for crude fiber (CF) (r('2) = .87). Errors in predicting animal responses to forages were greater than those in predicting chemical composition of the forages.