Impact of stocking density on beef heifer productive performance and health through hematology and longissimus dorsi ultrasound

Stocking density is one factor that can stimulate stress conditions in beef cattle farming, negatively impacting animal health and performance. The aim of this study was to evaluate hematology and longissimus dorsi ultrasound in beef heifers housed at two different stocking densities. A total of 54 Charolais heifers, 27 animals in each trial for two consecutive years, were randomly divided into two groups at arrival: high stocking density group (HIGH_D, 5.54 m 2 /animal; N = 26), and low stocking density group (LOW_D, 10.3 m 2 /animal; N = 28). A longitudinal study design was applied and animals were evaluated with blood sampling and longissimus dorsi ultrasound at arrival (D0), and after 30, 60, 90 and 120 days (D30, D60, D90, and D120) until the slaughtering. Body weight was measured at D0, D60, and D120 to calculate average daily gain (ADG) for the periods D60-D0, D120-D60, and D120-D0. Finally, the carcass yield and quality were obtained at the slaughterhouse. Statistical analysis was conducted with linear mixed models. The LOW_D had a greater body weight at D120, as well as higher ADGD120_D0, ADGD120_D60, and carcass yield compared to HIGH_D. The same group had also lower neutrophils and greater lymphocytes between D60 and D120, and lower monocytes between D90 and D120. Instead, HIGH_D had an increase in neutrophils and monocytes, and a decrease in lymphocytes. Despite both groups were within physiological ranges, the HIGH_D condition could be related to a slightly stress condition. Moreover, the LOW_D showed a greater muscle thickness and ribeye area from D30, back-fat thickness from D60, and intramuscular fat from D90 until D120. In conclusion, this study confirmed that stocking density significantly affects beef heifer performance and health, with animals housed at 10.3 m 2 /animal having better growth outcomes, ultrasound fat deposition pattern, and muscle growth.