Levels of LH, progesterone and estradiol-17β during natural and PGF 2α-induced estrus in Indobrazil and Brown Swiss cows in the tropics

Abstract

A comparison was made under tropical conditions between seven Indobrazil (IB) and six Brown Swiss (BS) cows with regard to the blood levels of luteinizing hormone (LH), progesterone (P 4) and estradiol-17β (E 2) during a PGF 2α-induced estrus and the natural estrus of the following cycle. After a double injection of 25 mg of PGF 2α 11 days apart, blood samples were taken every 3 h for 5 days, and this bleeding regime repeated for another 5 days starting on day 18 of the cycle that followed the second injection. Estrus occurred at 75.0 ± 6.1 and 69.4 ± 5.3 h after injection in IB and BS, respectively (NS). There was a decrease in P 4 concentration after PGF 2α and levels lower than 1.0 ng/ml were detected 24 h after the injection. The levels of P 4 decreased again at the end of the following estrous cycle from 60 to 30 h before the natural estrus in IB and BS. Estrogen concentrations were extremely variable and differences were not significant. The highest levels of E 2 were 23.7 and 24.7 pg/ml in the induced estrus and 15.2 and 25.5 pg/ml in the natural estrus of IB and BS cows, respectively; the peak value was observed on average 20 h before estrus in all groups. No significant differences between IB and BS were found in the concentration of LH, the peak occurring almost at the onset of the estrus (4.9 ± 0.6 h IB and 6.8 ± 0.6 h BS), except when the area under the LH curve was compared; here a significant effect of breed on LH concentration was found ( P < 0.05).