173 ESTRADIOL-17β CONCENTRATIONS IN BLOOD AND MILK DURING SUPEROVULATORY TREATMENT IN DAIRY COWS

Abstract

In cows, estradiol-17β is usually used to synchronize follicular wave emergence during superovulatory treatment. This approach, however, raises some concerns about the presence of estrogens in bovine products and their possible association with some human estrogen-sensitive cancers. The objective of this study was to determine estradiol-17β concentrations in blood and milk of dairy cows after i.m. injection of estradiol-17β and to compare these concentrations to those obtained during standard superovulation protocols. Six cows were used for this experiment. On Day 0, corresponding to Day 7 of their ensuing cycle, cows received 4.5 mg of estradiol-17β (Gentes et Bolduc, St-Hyacinthe, Québec, Canada) via i.m. injection and a progesterone-releasing vaginal insert (1.9 g of progesterone, CIDR, Pfizer Animal Health, Kirkland, Québec, Canada). Blood and milk samples were taken at 0, 24, 48, and 72 h after injection. From Day 4 evening to Day 8 evening, the cows received a total of 380 mg of NIH-FSH-P1 (Folltropin-V, Bioniche Animal Health, Belleville, Ontario, Canada) administered i.m. through 9 injections of decreasing dose (from 70 to 20 mg) at 12-h intervals. On Day 7, the cows received 2 injections consisting of 500 μg of cloprostenol (prostaglandin F2 α analogue, Estrumate, Shering-Plough, Pointe-Claire, Québec, Canada) given approximately 12 h apart and vaginal inserts were removed 12 h after the last injection. Artificial insemination was performed on Day 9 and 10 after treatment with 100 μg of GnRH i.m. (Cystorelin, Merial Canada Inc., Baie Urfe, Québec, Canada). A second batch of blood and milk samples was taken at Day 8, 9, 10, and 11. Measurement of estradiol-17β was performed with an IMMULITE chemiluminescent counter using an IMMULITE Estradiol Kit (Siemens Diagnostic Products Corporation, Los Angeles, CA, USA). Concentrations of estradiol-17β in blood (37.1 ± 15.6 pg mL^-1 at 24 h, 19.1 ± 14.2 pg mL^-1 at 48 h) and milk (38.4 ± 29.5 pg mL^-1 at 24 h, 9.3 ± 4.9 pg mL^-1 at 48 h) were significantly higher after i.m. injection of 4.5 mg of estradiol-17β. In comparison, superovulation heat (Day 9 to 11) increased estradiol-17β concentrations in blood (20 ± 13.6 pg mL^-1 at 24 h, 32.5 ± 16.3 pg mL^-1 at 48 h) but not in milk.