Steer performance, grazing behavior, and stress responses under different stock densities on dormant old world bluestem

Rotational grazing increases stock density by forcing animals into smaller areas while keeping animal numbers constant. It is unknown how this increased density affects the animal. Yearling Mexican crossbred steers (189 kg+ 17) were used to evaluate performance, biting rate, grazing time, and relative stress effects at different stocking densities on dormant old world bluestem over 2 years. Various densities (DEN) were achieved by using three grazing systems; season-long or continuous, 3-paddock rotation, and 6-paddock rotation. Steer performance, serum cortisol concentration (CORT), biting rate (BR), grazing time, sleeping time (ST), and loafing time (LT) were examined. During the first year (YRl), season-long average daily gain (ADG) tended to decrease with increased DEN; however, no relationship was observed the second year (YR2) . Serum cortisol exhibited a trend to increase with DEN in 3 of 4 periods over the 2 years. No relationship between CORT and DEN was found for the first period of YR1. Biting rate in the morning before rotation tended to decrease with increasing DEN during YRl, but was not related during YR2. Evening BR following rotation increased with DEN for YR1 and YR2. Grazing time was not related to DEN, LT exhibited a trend to decrease with increased DEN, and ST was negatively related to DEN. Fecal analyses showed no relationship between diet quality and DEN during YRl or YR2. Stock density may not affect steer performance; however, cortisol concentrations may tend to increase. Biting rate following rotation increased with increasing density, but grazing time was not affected.