PS11-17. Associations Among Cardiac Traits, Body Temperature, Feed Efficiency, and Carcass Composition in Crossbred Angus Feedlot Steers – an Exploratory Study Based on Heart Scores.

Abstract In an exploratory study, thirteen Angus crossbred steers were monitored from weaning to harvest, selected from a larger group of 52 animals, based on heart score. During finishing, steers participated in a feed efficiency trial in which individual dry matter intake and feeding behavior were recorded daily using an automated intake control system. Each steer was fitted with an eartag sensor two weeks after processing to continuously record rumination time, eating time, and external ear temperature. Serum concentrations of cardiac troponin I (cTnI) were measured before harvest, and heart scores, heart measurements, and carcass composition were obtained postmortem. All variables were correlated to explore associations among cardiac traits, thermoregulatory responses, performance, and carcass outcomes. Heart score was treated as an ordinal variable (1 = normal, 5 = extremely remodeled); therefore, Spearman correlation coefficients were calculated, and Pearson correlation coefficients were calculated for all other continuous variables. Heart score was positively correlated with heart septum width (r = 0.69; P = 0.01). Serum cTnI concentrations were negatively correlated with gain:feed ratio (G:F; r = −0.66; P = 0.02) and average daily gain (ADG; r = −0.55; P = 0.05) and tended to be negatively correlated with slaughter weight (r = −0.51; P = 0.07). The width of the right auricle wall (RAW) was negatively associated with ADG (r = −0.59; P = 0.04) and backfat thickness (r = −0.59; P = 0.04), and tended to be negatively associated with G:F (r = −0.54; P = 0.08). Also, RAW tended to be positively correlated with time spent above the body temperature threshold (r = 0.50; P = 0.10). Body temperature, expressed as area under the curve (AUC; temperature × time), was positively correlated with intake rate (r = 0.62; P = 0.03), G:F (r = 0.73; P = 0.01), and slaughter weight (r = 0.68; P = 0.01), and tended to be positively correlated with dressing percentage (r = 0.54; P = 0.06). Time spent above the temperature threshold was negatively correlated with G:F (r = −0.67; P = 0.02). Together, elevated serum cTnI concentrations and increased right auricle wall thickness were associated with poorer growth performance, reduced feed efficiency, and a tendency toward lighter, leaner carcasses and greater thermal load, suggesting that subclinical cardiac remodeling may negatively impact productivity in finishing steers. The positive association between RAW and body temperature may reflect increased cardiovascular burden, but this finding should be interpreted cautiously because body temperature was also positively correlated with body weight and is influenced by intake, rumination, and heat production. Larger studies are needed to confirm these relationships and to identify potential biomarkers for cattle at increased risk of cardiovascular compromise in the feedlot.