Plasma Cortisol and Progesterone Responses to Low Doses of Adrenocorticotropic Hormone in Ovariectmized Lactating Cows

Chikako YOSHIDA, Toshihiko NAKAO
2006 Journal of reproduction and development  
The objective of this study was to describe the responses of the plasma progesterone and cortisol concentrations in ovariectomized lactating cows to low doses of adrenocorticotropic hormone (ACTH). The estrous cycles in 3 lactating cows were synchronized, and the cows were ovariectomized in the luteal phase. ACTH challenge tests were conducted at doses of 3, 6, 12 and 25 IU. Blood samples were collected at 30 min intervals, and the plasma progesterone and cortisol concentrations were analyzed
more » ... EIA. A concomitant rise in plasma progesterone and plasma cortisol was observed in cows treated with 12 IU or higher doses of ACTH. Significant increments in the plasma cortisol concentrations were observed at all doses of ACTH. The means (± SE) of the peak plasma progesterone concentrations after the 3, 6, 12 and 25 IU ACTH challenge tests were 0.6 ± 0.1, 1.3 ± 0.4, 1.5 ± 0.3 and 2.4 ± 0.3 ng/ml, respectively. The means of the peak plasma cortisol concentrations in the 3 cows after the ACTH challenge were 14.0 ± 1.5, 17.0 ± 2.5, 23.3 ± 3.0, and 33.3 ± 7.0 ng/ml, respectively. The effects of the doses, time after treatment, and their interaction on the plasma progesterone concentrations after the ACTH challenge were significant (P<0.01). Likewise, the effects of the doses, time after treatment, and their interaction on the plasma cortisol concentrations after the ACTH challenge were significant (P<0.01). The mean AUC values for the plasma progesterone and cortisol concentrations after the ACTH treatments were also significantly affected by the dose of ACTH (P<0.01 and P<0.05, respectively). A significantly positive correlation was obtained between the peak plasma progesterone and cortisol concentrations after different doses of ACTH (r=0.7, P<0.05). The results suggest that lactating dairy cows are capable of secreting a significant amount of adrenal progesterone, reaching up to the minimal concentration necessary to cause suppression of estrus in response to 12 IU ACTH (P<0.01). The concomitant plasma cortisol concentration was 23.3 ng/ml. h i g h h e a t d e t e c t i o n r a t e i s a p r i m a r y require ment for effective reproductive management of dairy herds [1, 2] . Recently, the duration of estrus in lactating cows has been reported to be substantially shortened [3] [4] [5] [6] , and the percentage of cows exhibiting standing estrus has been decreased [6] [7] [8] [9] . Some studies have indicated that cows or heifers with weakened estrous signs show suprabasal
doi:10.1262/jrd.17051 pmid:16988492 fatcat:tamrqixzxndrfkzfdkdpxkrsiq