Physiological indicators of tick-induced stress in grazing
MetadataShow full item record
Three studies utilizing a single group of growing beef steers were conducted to ascertain the effects of tick stress on cattle and to evaluate the use of bio-forensic techniques of detection. Steers (n = 28, 194 ± 3.0 kg) were randomly assigned to one of four treatments in a 2 x 2 factorial arrangement: moderate (14.0 ± 1.0% CP, 60 ± 1.5% TDN) versus low (7.0 ± 1.0% CP, 58 ± 1.5% TDN) plane of nutrition, and control (no tick) versus tick treatment (300 pair of adult (Amblyomma americanum) per treated animal). Steers were individually fed experimental diets ad libitum for 35 days prior to and 21 days following the start of tick infestation (day 0), with peak tick feeding occurring 10 to 14 days post tick infestation. In study 1, blood was sampled on day -7, 0, 7, 8, 9, 10, 11, 13, 17 and 21, and plasma analyzed for metabolic and endocrine indicators. Within the low plane of nutrition, IGF-1 (ng/ml) was greater in control (P < 0.05) than in the tick treated (139.57 ± 9.3 vs 111.4 ± 9.3) group. Within the moderate plane of nutrition, tick treated cattle had higher (P < 0.05) plasma cortisol than nontreated. In study 2, fecal samples were analyzed for metabolic, endocrine and immunologic indicators. Fecal cortisol was the only constituent measured that was affected by treatment and not by plane of nutrition. The highest average daily fecal cortisol observed was for day 13, during peak tick feeding and after six days of repeated blood sampling. In study 3, near infrared spectra were obtained in the 1100-2498 nm range. Spectra were assembled into groups by plane of nutrition, treatment, and by plane of nutrition by treatment. Periods of 7 ± 1 days correspond to significant delineations in the tick feeding cycle. There were differences in pre-infestation versus infestation fecal spectra within the tick treated groups in both the moderate and low planes of nutrition. These differences can not be wholly attributed to tick treatment, but may have also been affected by blood sampling stress.
Tolleson, Douglas Ray (2007). Physiological indicators of tick-induced stress in grazing. Doctoral dissertation, Texas A&M University. Available electronically from