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Title:   Author  item
                                            Foote, Andrewitem
                                            Hales Paxton, Kristinitem
                                            Tait Jr, Richarditem
                                            Berry, Elaineitem
                                            Lents, Clayitem
                                            Wells, James

                                                         - *Jim*item
                                            Lindholm-Perry, Amandaitem
                                            Freetly, Harvey
  Submitted to: Journal of Animal Science
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 10/21/2015
                                    Publication  Date: 1/11/2016
                                    Publication URL: https://handle.nal.usda.gov/10113/61807Citation: Foote, A.P., Hales, K.E., Tait Jr, R.G., Berry, E.D., Lents, C.A., Wells, J. E., Lindholm-Perry, A.K., Freetly, H.C. 2016. Relationship of glucocorticoids and hematological measures with feed intake, growth, and efficiency of finishing beef cattle. Journal of Animal Science. 94(1):275-283. doi: 10.2527/jas2015-9407Interpretive Summary: Physiological mechanisms that lead to improved growth and efficiency of beef cattle could improve selection of cattle for valuable traits that would improve the sustainability of the beef industry.  This experiment was performed to evaluate the association of two such mechanisms, glucocorticoids and immune function, with feed intake, growth, and feed efficiency.  Basal glucocorticoids were evaluated by measuring corticosterone, a glucocorticoid, in the feces of beef cattle.  Another glucocorticoid, cortisol, was measured in blood after cattle had been processed.  None of these measures were associated with feed intake; yet, higher concentrations of cortisol were observed in faster growing and more efficient cattle.  Immune function, measured using blood cell counts, were slightly associated with feed intake, growth, and efficiency, but depended on the sex of the cattle.  Immune status, an indicator of over-all health in cattle, was not greatly associated with any production traits.  It appears that glucocorticoid concentrations in cattle could be an indicator of feed efficiency in feedlot cattle.
                                Technical Abstract: The objective of this experiment was to determine the association of glucocorticoids and markers for immune status in finishing beef steers and heifers with DMI, growth, and efficiency.  Calves (n = 236) were individually fed a finishing ration for 84 d with BW measured every 21 d.  Blood samples were collected via jugular venipuncture for metabolite (glucose and lactate) and cortisol analysis and rectal grab samples of feces were collected for corticosterone analysis on d 83 of the experiment.  Plasma cortisol was not correlated to DMI (r = -0.08; P > 0.05) or BW-adjusted DMI (r = -0.03; P > 0.05), but was negatively correlated with ADG (r = -0.17; P < 0.01) and G:F (r = -0.20; P < 0.01) and positively correlated to residual feed intake (RFI; r = 0.14; P < 0.05).  Fecal corticosterone was positively correlated to BW-adjusted DMI (g DMI/kg BW; r = 0.15; P < 0.05) and RFI (r = 0.23; P < 0.01) and negatively correlated to G:F (r = -0.18; P < 0.01).  Using a mixed model analysis, none of the metabolites or hormones were associated with DMI (P > 0.05), but fecal corticosterone was positively associated with BW-adjusted DMI in heifers only (P = 0.04).  Plasma lactate (P < 0.01) was and plasma cortisol (P < 0.10) tended to be negatively associated with ADG.  Plasma cortisol (P < 0.05) and fecal corticosterone tended (P < 0.10) to be negatively associated with G:F.  Fecal corticosterone was positively associated with RFI in heifers (P < 0.04).  In a mixed model analysis, total leukocyte count was positively associated with ADG (P < 0.04) and tended to be positively associated with G:F (P < 0.06).  Amongst leukocyte subtypes, neutrophil count was positively associated with ADG in steers (P < 0.02) and monocytes were positively associated with ADG in heifers (P < 0.03).  Lymphocyte counts (LY) in steers were negatively associated with DMI (P = 0.03) and BW-adjusted DMI (P < 0.03).  In heifers, LY tended to be positively associated with DMI (P < 0.09) and BW-adjusted DMI (P < 0.06).  Lymphocyte count was also positively associated with ADG (P < 0.01) and G:F (P = 0.05) in heifers.  The association of production traits with immune status seems to be different between steers and heifers.  There was a stronger relationship of cortisol than fecal corticosterone to feed efficiency measures, suggesting that an animal’s response to stress may be more important than basal glucocorticoid status for feed efficiency.


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