Dexamethasone influences endocrine and ovarian function in dairy cattle

Multiparous nonlactating Holstein cows were used to determine the effect of dexamethasone on ovarian follicular development and plasma hormone concent rations. Animals were randomly divided into two groups, control (C; n = 5) and treatment (T; n = 6), but managed as one group. Both groups were synchr onized with two injections of PGF(2 alpha) (25 mg i.m.) 11 d apart. One day after ovulation (d 0) the T group received a daily injection of dexamethas one (44 mug/kg of body weight; i.m.) until the first dominant follicle stop ped growing or up to d 12 postovulation. The C group received vehicle injec tions. Blood samples were collected daily from all cows. Concentrations of LH and FSH did not differ between the C and T cows, whereas progesterone co ncentrations were lower in T than in C cows from d 4 onward. Treatment x da y interaction influenced plasma insulin concentrations such that T cows had insulin concentrations 2.9- to 6.0-fold those of C cows between d 2 and 9. Dexamethasone decreased IGF-I and -II concentrations from d 5 onward. Conc entrations of plasma leptin and the various IGF binding proteins were not a ffected by dexamethasone. Total number of follicles (greater than or equal to5 mm) and plasma estradiol concentrations were less in T than in C cows o n d 0, 1, and 4. The growth rate of the dominant follicles and maximum diam eter of the dominant and subordinate follicles were not affected by dexamet hasone. The diameter of the CL was 21 to 39% larger in T than in C cows bet ween d 6 and 10. Treatment x day interaction influenced plasma cholesterol concentrations such that cholesterol levels decreased 46.8% in T cows and 1 9.5% in C cows between d 0 and 10. Plasma glucose concentrations were great er in T than in C cows between d 1 and 10. In summary, dexamethasone had si gnificant effects on metabolism without a major impact on growth of the fir st-wave dominant follicle. Dexamethasone-induced suppression of luteal func tion was associated with decreased plasma IGF-I and -II concentrations.