42. Impact of Ultra-high Stocking Density Grazing System on Cattle Behavior and Productivity

Abstract Ultra-high stocking density (UHSD) grazing involving the strategic rotation of livestock through multiple paddocks at high densities has been proposed to enhance pasture recovery and soil health, whereas cattle productivity is unexplored. This study evaluated the impact of UHSD grazing on cattle behavior and physiology. Fifty Angus crossbred calves were sorted by sex and initial body weight (BW; 274 ± 3.7 kg) and assigned to 1 of 10 paddocks (2 ha/paddock; 3 steers and 2 heifers per paddock) stockpiled with the site’s predominant forage species. Each paddock was randomly assigned to either 1) UHSD grazing (stocking density of 55,000 kg of liveweight/ha) or continuous grazing (stocking density of 625 kg of liveweight/ha; CON) for a 28-d grazing period. The UHSD treatment was implemented using a combination of permanent and temporary fencing to established required stocking density and small plots. Calves were moved within UHSD treatment plots once grazing threshold of 7 cm residual height was met. Soil bulk density and penetrometer resistance were collected on d 0 and 28, and forage biomass was recorded weekly. Calves were fitted with an ear tag (CowManager, Select Sires, OH) on d 0 to record behavioral responses. Calf BW and exit velocity were collected weekly. Data were averaged by week, and the impact of treatment, week, and their interaction were analyzed using the MIXED procedure of SAS, with differences evaluated using Least Squared Means. Soil bulk density did not differ (P = 0.25), whereas penetrometer resistance was greater (P = 0.05) in UHSD paddocks vs. CON. Available forage biomass did not differ (P = 0.40) between treatments. Exit velocity did not differ throughout the experiment (P = 0.26) between UHSD and CON calves. Weekly average proportion of time spent eating and classified as not active was reduced (P < 0.01) during the experiment for UHSD vs. CON calves. A treatment × week interaction was detected (P < 0.01) for weekly average proportion of time spent ruminating, which was greater (P < 0.01) during week 1 and tended (P = 0.08) to be greater during week 2 for CON vs. UHSD. A treatment × week interaction was detected (P < 0.01) for weekly average proportion of time spent highly active which was greater (P = 0.02) during week 4 in UHSD vs. CON calves. Overall calf average daily gain was greater (P < 0.01) in CON vs. UHSD calves (0.58 and 0.14 kg/d, respectively, SEM = 0.06), accordingly final BW tended (P = 0.07) to be greater in CON vs. UHSD calves. Collectively, results from this experiment suggest that UHSD grazing increases soil compaction and compromises short-term cattle growth performance. Further research is warranted to investigate UHSD strategies with mature cattle.