Use of n-alkane and fecal near infrared reflectance spectroscopy (fNIRS) methods and traditional prediction equations to estimate intake of RFI-divergent beef cattle grazing annual and perennial pastures

Abstract

These studies i) compared pasture intake of beef heifers via n-alkane, fNIRS (direct, or indirect via fecal C31 and C32) and three equation-based methods; ii) examined the relationship between pasture intake estimates and RFI rankings; and iii) assessed suitability of swath-grazed triticale for n-alkane studies by examining its n-alkane and starch profiles, and morphology (via plant part weights). When grazing meadowbrome pasture, DMINRC was least variable and greater than DMIAlkane, DMIfNIRS and DMIfNIRSC31C32. RFIfat was significantly correlated with direct or indirect fNIRS methods (P < 0.05) for LAC 2015 heifers only. DMIAlkane was correlated to RFIfat in 2015 (P < 0.05) but not in 2016. No equation-based DMI method differed significantly between RFIfat groups. Grazing triticale swaths, Trial 1 starch and C31 concentrations (P ≤ 0.0002) were lower in PM compared to AM samples. In Trial 2, C31 and C32 concentrations and weights differed (P < 0.0001) between plant parts.