Effect of transportation stress on cytokine gene expression, hematic biometry and blood chemistry in heifers
Transportation is probably the most stressful event cattle can experience affecting health, performance, meat quality and causing considerable economic losses. The objective of this study was to determine the effect of long-term transport stress on blood chemistry, hematological and cytokine gene expression measurements. Blood samples from 16 Bos taurus x Bos indicus heifers from a feedlot located in northeastern México, were obtained by coccygeal venipuncture. Heifers weighed an average of 300 kg. Samples were obtained from eight heifers newly arrived from a 40-h road trip (0 DPA) as they were unloaded and restrained in a hydraulic chute to receive routine weighing and physical check-up, and the other 8 heifers were in their twenty-fifth day post-arrival (25 DPA). Cytokine gene expression, hematic biometry and blood chemistry were analyzed. For gene expression, blood samples were stabilized for RNA extraction and RNA yielded was quantified and standardized. Specific primers were used for the amplification of cytokines TNF-α, IFN-γ, IL-2 and glyceraldehyde 3-phosphate dehydrogenase (GAPDH), the latter used as an internal control gene. Amplified products were analyzed by electrophoresis and quantitative values were calculated for each band using the myImageAnalysis software from Thermo Scientific™. Blood chemistry results showed higher concentrations of albumin (P = 0.013), amylase (P = 0.027), alanine aminotransferase (P = 0.003), bilirubin (P = 0.001) and cholesterol (P = 0.013) in the 0 DPA group. Hematocrit (P = 0.022) and hemoglobin (P = 0.001) values were lower in heifers at 25 DPA. Cortisol concentration was higher (P = 0.001) in the 0 DPA group. On the quantitative gene expression analysis, we observed that the expression of TNF-α was greater (P = 0.001) in the 25 DPA group. At the TNF-α amplification two un-specific bands were found, only in the animals of the 0 DPA group. These bands were sequenced, and BLAST analysis suggests that they correspond to bovine lymphotoxin (LT). Literature shows that LT and TNF-α are coded in the same gene, even though, they have different promoters and polyadenylation sites. In conclusion, homeostatic impairment, high stress levels and immunological changes were apparent in recently transported heifers as evidenced by the blood chemistry and hematological measurements, the higher cortisol concentration, the reduction in cytokine TNF-α expression and LT co-expression. Further studies should look into the mechanism that promotes LT expression in animals exposed to transport stress, to probably be used as a biomarker for transport stress.
Keywords: Stress, transport, heifers