PSIII-4 - Exploring the behavioral effects of glycerol supplementation in ruminally cannulated cows grazing wheat pasture

Abstract: Energy intake and metabolism plays a key role in the control of DMI, fermentation processes, and grazing behavior of beef cattle, and is likely affected by intertwined relationships between forage availability and stage of maturity, offering of energy supplements and climate- and animal-related factors. Nine ruminally cannulated mixed-breed nonlactating cows (564.4 ± 101.6 kg initial BW) grazing wheat pasture were used in a split-plot design with the objectives of evaluating the effects crude glycerine supplementation and forage maturity on grazing behavior. Treatment was the main plot, and stage of forage maturity was the subplot. Treatments were unsupplemented control (CON) and crude glycerine supplementation (SUP). Crude glycerol (37.2% glycerol, DM basis) was offered at 0.11% of BW (DM basis) and dosed intraruminally via rumen cannula at 0700 and 1900 h daily. The stages of wheat pasture maturity were March (MAR; vegetative stage) and April (APR; early reproductive stage). All cows were fitted with LoRa WAN tracking collars, housing GPS and triaxial accelerometers and allowing real-time inspection of cow position and activity data through time. Hourly (days 10 and 23) and daily change of walking distance (m), activity index and budget for grazing, resting, and walking time (min) were analyzed with a repeated measure mixed model for the split-plot design. Walking distance (1200 ± 13 m), activity index (10,006 ± 122), resting time (607 ± 5 min), grazing time (662 ± 8 min) and walking time (171 ± 8 min) were not affected (P ≥ 0.52) by crude glycerine supplementation or by stage of forage maturity (P ≥ 0.07), but varied (P < 0.001) by day and by hour of day, likely indicating circadian effects on meal frequency and duration associated with the hour of the day and forage depletion through time. Grazing behavior was more likely affected by climate, pasture, animal, and management variables and less affected by GLY dose. Results indicate that crude glycerine may be used in supplements for cattle grazing wheat pasture to increase energy intake and without adversely creating associative or substitution effects, grazing behavior or sacrificing pasture utilization.