The effects of acclimation to confinement on gonadotrophin and cortisol secretion during the estrous cycle of the ewe

Abstract

The purpose of the study was to examine the effects of acclimation to confined housing on tonic gonadotrophin, cortisol and progesterone secretion in ewes at different stages of the estrous cycle. On days 4, 12 and 16 of the estrous cycle separate groups of eight ewes were blood sampled every 5 min for 6 h. Of the eight ewes bled at each stage of the cycle four were moved from outside drylots to small pens in a building 2 d prior to blood sampling and four were moved 4 d prior to sampling. All blood samples were analyzed for concentrations of LH and FSH and one sample for each hour of intensive bleeding, for each ewe, was analyzed for cortisol and progesterone. All hormone concentrations were obtained by radioimmunoassay. On day 4 of the estrous cycle LH pulse frequency and mean serum concentrations of LH were higher, but mean FSH concentrations were lower, in ewes confined for 4 d, compared to those confined for 2 d (P < 0.05). On day 12 of the cycle, mean serum LH concentrations only were higher in ewes confined for 4 d (P < 0.05). At day 16 no differences were seen between ewes confined for 2 or 4 d. Serum concentrations of progesterone, cortisol and LH pulse amplitude did not vary significantly between ewes confined for 2 or 4 d. However, in ewes confined for 4 d, serum concentrations of cortisol fell from day 4 to day 16 of the estrous cycle (P < 0.05). We conclude that acclimation to confined housing in the intact cyclic ewe is reflected in changes in tonic LH secretion at stages of the estrous cycle when serum concentrations of cortisol are high. Key words: LH, FSH, cortisol, confinement, cyclic ewe