Physiological responses of beef cattle to Gulf Coast tick (Acari: Ixodidae) infestations.

Nine yearling crossbred beef steers, Bos taurus L., were used to examine physiological responses to Gulf Coast tick, Amblyomma maculatum Koch, infestation. Steers were stanchioned indoors in individual environmentally controlled rooms. On day 0, each animal received 0, 25, or 75 pairs of ticks. Physiological variables measured daily were feed intake, heart rates, rectal temperatures, and respiration rates. Blood samples were collected from each animal on days 7, 21, and 42 for serum constituent analysis. To monitor metabolic hormone status, intensive blood samples were collected hourly for 6 h on days 21 and 42. Throughout the treatment period, feed intake values were similar among treatments resulting in comparable body weight at the end of the trial. Heart rates and rectal temperatures were unaffected, however, respiration rates of steers infested with 25 pairs of ticks were higher than the other treatment groups. Treatment effects were detected in uric acid concentrations on day 7 in steers infested with 75 pairs of ticks. Treatment effects were detected in total, direct and indirect bilirubin, gamma-glutamyl transpeptidase, and aspartate amino transferase concentrations. Likewise, creatine kinase concentrations were higher in the tick-infested steers on day 7. Elevated white blood cell counts were observed in tick-infested steers. All other serum components were similar and were within their normal ranges. Serum insulin, prolactin, growth hormone, and cortisol concentrations were unaffected by tick infestations. Gulf coast tick infestation resulted in altered blood composition indicative of infection caused by tick feeding habits.