Evaluation of adrenal function, growth, carcass characteristics, blood metabolites, hematological and immune parameters in Angus, Brahman, Bonsmara X Angus and Bonsmara beef steers

Adrenal function, blood metabolites, hematological parameters, growth, and carcass characteristics were compared in tropically-adapted (Brahman,) intermediate (Bonsmara and Bonsmara X Angus crossbred,) and temperate (Angus; n=10 each) beef steers. An adrenal gland challenge was conducted, entailing serial blood collection at 15-min intervals for a 12.5-h period, with administration of exogenous ACTH (0.1 IU/kg BW) 2.5-h into the experiment. Steers were maintained on Coastal bermudagrass pastures overseeded with ryegrass for five month; body weights and blood samples were obtained every 21 days. An anterior pituitary/adrenal gland challenge was conducted, entailing serial blood collection at 120, 90, 60 and 30 min prior to, and 10, 20, 30, 60 and 120 min following administration of exogenous CRH (0.1 ug/kg BW). Physical and physiological signs of heat stress were assessed, and blood samples were obtained for analysis. Exit velocity was measured. Carcass characteristics were determined post-slaughter. Statistical analysis was conducted using ANOVA for repeated measures, using least square means and Pearson??????s and Spearman??????s correlation analyses. Bonsmara and Bonsmara X Angus had lower basal cortisol (CS) than Angus and Brahman steers. Angus steers had greater adrenal responsiveness to ACTH, and responded faster to CRH than the other breedtypes. Bonsmara steers were slower in responding to CRH, and returning to basal CS following ACTH or CRH administration. Angus and Bonsmara X Angus grew faster during the finishing phase than Brahman or Bonsmara steers. Angus had higher quality grades than other breedtypes; rib-eye area and hot carcass weight were greater in Angus than Brahman steers, but similar among Angus, Bonsmara X Angus and Bonsmara steers. Angus and Brahman were less docile than Bonsmara and Bonsmara X Angus steers. Angus steers had higher respiration rates and serum concentrations of sodium, lower aldosterone during moderate heat exposure, and lesser serum concentrations of glucose, urea and cholesterol than tropically-influenced breedtypes. Angus had rectal and surface temperatures similar to those of Brahman, but greater than those of Bonsmara X Angus or Bonsmara steers. Intermediate breedtypes like the Bonsmara provide a compromise to producers, allowing them to address the demands of consumers while raising cattle better suited to survival in tropical climates.