Effect of stress due to ultrassonography on plasma cortisol and progesterone (P4) concentrations during oestrous cycle in ewes

The primary purpose of this study was to observe the effects of repeated transrectal ultrassonography on plasmatic concentrations of cortisol and progesterone (P-4) in ewes during estrous cycle. Seven Bergamasca ewes (2-5 years of age), received two luteolytic doses of cloprostenol at 7 day intervals during the breeding season. Estrous was detected using a vasectomized ram. Ovaries were examined daily using transrectal ultrassonography. The ewes were studied starting one day before the second PGF(2 alpha) injection until 10 days after ovulation (day 0 = ovulation). Jugular vein blood samples were collected daily and after ultrassonography for plasma cortisol and P-4 measurement. There was no effect of the repeated transrectal ultrassonography on plasma concentrations of cortisol. However, analysis of variance indicated that cortisol concentrations varied over time. Higher plasma concentrations were detected after ultrassonography on day-1 (1.74 +/- 0.76 mu g/dL) and day-0 (2.9 +/- 0.76 mu g/dL). Rise in plasma cortisol during the first days of stress reflected the emotional reaction to the stressor. However, mean P-4 concentrations were unaffected by transrectal ultrassonography on day-1 (1.28 +/- 0.32 ng/mL) and day-2 (1.53 +/- 0.32 ng/mL) when compared to those before ultrassonography on the same days (0.95 +/- 0.32 and 1.10 +/- 0.31 ng/mL, respectively). In summary, endocrine responses of cortisol and P-4 plasma concentration to repeated transrectal ultrassonography were unaffected during follicular and early luteal phase in ewes.