Assessing Plant-Wax Markers as a Tool to Estimate intake and diet Composition in Beef Cattle

Estimating feed efficiency of ruminants in grazing environments is difficult due to challenges in measuring intake and diet composition of animals that are freely grazing. Plant-wax markers, especially n-alkanes (ALK), have been shown to be a potential tool to calculate intake and diet composition. Two indoor experiments were conducted in successive years to assess ALK reliability to facilely estimate DMI (EDMI) and diet composition. Heifers were fed a ration of 69.8% corn silage and 30% ground alfalfa with a daily supplement containing a ALK marker (C32). Using a pooled fecal sample increased the correlation between observed DMI and EDMI (in 2015, r =0.79; in 2016, r = 0.65) when compared to daily intakes methods. Furthermore, the EDMI was sensitive to diet composition estimates due to the forages having two distinctly different concentrations of C31 and C33. A series of grazing studies followed each experiment. The predominant plant species in all studies (smooth bromegrass and Kentucky bluegrass) had ALK profiles that allowed 10% difference in diet compositions to be distinguished (P \u3c 0.02). Differences in concentrations of marker C33 between plants resulted in unrealistic EDMI. When EDMI based on the C31:C32 ratio were compared to observed intakes from the indoor studies, the results were highly variable (0.01 \u3c r2 \u3c 0.99), which could be due to many factors including animal behavior and forage availability. Despite the lack of fine demarcations, sensible intakes were obtained in a grazing setting. The plant-wax methodology therefore shows promise for commercial use