Effects of Acute and Chronic Stress on Immune- and Inflammatory-response Gene Expression in Beef Calves

Transport stress research has shown correlations among stress, morbidity, and mortality in calves subjected to the traditional U.S. market system, indicating the possibility of compromised immune function. The objective of this study was to determine if expression of specific immune and inflammatory response genes differed between calves that were subjected to either an acute stress (AS, handled and weaned for 1.5 h) or a chronic stress (CS, weaned, handled and transported for 3 to 4 d). Two groups of forty calves, Bos taurus (n = 20) and crossbred calves (n = 20), weighing 181 kg to 250 kg were used in each of two trials. Jugular veni-puncture blood samples (9 ml) were collected from AS calves 1.5 h after the start of handling and separation from their dam. Samples were collected from CS calves during processing after arrival at a north Texas feed lot. RNA for gene expression analysis was extracted from peripheral blood leukocytes obtained from blood samples by a filtration method. During the second trial, the filtrate was centrifuged for measurement of plasma cortisol. A diagonal covariance mixed model ANOVA was used to determine effects of treatment, breed, and breed by treatment interaction on cortisol concentrations. Expression values for each gene were analyzed using linear models that considered the effects of treatment (AS and CS) and breed (Bos taurus and crossbred calves) comparing each trial separately. Mean plasma cortisol concentrations did not differ between AS (16.40 +/- 1.08 ng/ml) and CS calves (18.06 +/- 1.14 ng/ml) (P > 0.296). The interaction of effects was detected for 2 genes in Trial 1, and 3 genes in Trial 2 (P < 0.029). Breed was influential for 5 genes in both Trial 1 and 2 (P < 0.046). Significant differences were found in relative quantification for 30 genes in Trial 1 and 36 genes in Trial 2, in which CS calves had greater expression than AS calves (P < 0.047). Fifteen of those genes were common between the two trials with mean treatment differences of RQ values from the 15 genes ranging from 0.309 to 913.19, excluding outliers. Similar elevated cortisol concentrations in both the AS and CS calves indicated that both groups experienced significant stress. However, changes in gene expression differences were greater in the calves subjected to CS, indicating that gene expression may be more useful than cortisol for identifying detrimental long-term stress.