Characteristics of protein-protease inhibitors, 17-beta estradiol and progesterone in the blood of heifers returning to estrus following LH/FSH-RH treatment]

Tests were performed to study the inhibitive capacity of protein-protease inhibitors, 17-beta estradiol, and progesterone in the blood serum of 21 heifers returning to oestrus which had been treated intramuscularly with 400 microgram LH/FSH-RH. Four selected heifers were examined as to the relationships between the concentrations of 17-beta estradiol, progesterone and the inhibitive capacity of the serum. Heifer no. 1 had low concentrations of 17-beta estradiol and higher concentrations of progesterone (average levels 7.8 and 657.4 pg ml-1 of serum). On the other hand, heifer no. 4 was found to have higher concentration of 17-beta estradiol and lower values of progesterone (average levels 28.3 and 325 pg ml-1 of serum). Having shown heat, the heifers were fertilized and remained in calf. Heifer no. 2 with a low concentration of progesterone (292 pg ml-1 of serum) and 17-beta estradiol (12.4 pg ml-1 of serum), as well as heifer no. 3 with a high concentration of both (830 pg ml-1 of serum and 22.7 pg ml-1 of serum, respectively) showed no heat and they were not mated. Heifers with significant differences in the concentrations of progesterone and 17-beta estradiol and with low values of protein-protease inhibitory capacities remained in-calf, whereas heifers with lower progesterone and 17-beta estradiol values, or adversely, with higher inhibition values, showed no heat. Synthetic LH/FSH-RH was found not to increase the amount of protein-protease inhibitors in heifer serum, as distinct from the cervical mucus of breeding cows treated with gestagens in heat synchronization.