Serum progesterone in heifers with different luteal activity treated with vaginal devices

The progesterone (P4) device is a very important step in the ovulation control in Timed Artificial Insemination (TAI) protocols. It represents about 43% of the hormone costs, thus it has been the subject of several studies on efficiency of the reused device as an alternative to reduce TAI costs. However, to our knowledge, profiles for P4 release in animals with different endogenous concentrations of P4 are not clearly described. This study aimed to evaluate serum concentration of P4 in females with different ovarian conditions - related to luteal activity - and treated with a new intravaginal device (1g of P4) for 8 days. Thirty normally cyclic crossbred heifers were divided into three groups: for G1 and G2, P4 device was inserted (D0) seven days after ovulation (7 day old CL). Additional PGF (0.15 mg of D-cloprostenol) was given three days later to promote luteolysis in the G2 group. For G3, CL was killed before P4 insertion and the exogenous progesterone was the only source of this hormone. Blood samples were collected on D0, D3, D5 and D8 and P4 concentration was measured by radioimmunoassay (RIA). Means for P4 concentration were compared among groups in each day and within the group among days using the Tukey test. Before P4 device insertion (D0), P4 levels were higher (P0.05) among groups on D8 (3.1±1.3, 1.8±0.8 and 1.6±0.6ng/mL, respectively, for G1, G2 and G3). Progesterone increase after P4 insertion (D3 - D0) was higher (P