| dc.description.abstract | This research evaluated the influence of equine chorionic gonadotropin applied on day 6
of the J-synch protocol, on the follicular response and the concentration of luteinizing
hormone in Holstein Friesian dairy heifers from the Ecuadorian high tropics. Four heifers
from 16 to 24 months of age, clinically healthy and cyclical, were used. In a first stage, a
“J-synch” heat synchronization protocol was applied, which consisted of: day 0,
application of estradiol benzoate (2 mg) + DIV-P4 (0.5 g); day 6, removal of DIV-P4 +
prostaglandin F2α (500 µg); and day 9 gonadorelin (100 µg). In a second stage, after 30
days, the heifers were subjected to the same J-synch protocol with the addition of 400 IU
of eCG on day 6 of the protocol. In both stages, the dominant follicles, ovulation, and
corpora lutea were evaluated ultrasound from day 6 to day 10. In addition, at 50, 55, 60,
and 65 h, the serum LH concentration was assessed using the chemiluminescence assay.
The results showed that the follicular wave was synchronized in only one heifer (No. 2) in
the two protocols, recording an LH peak between 50 h (3.74 mIU/ml) and 55 h (3.88
mIU/ml). ) and ovulating around 72 h after the removal of DIV-P4. In the other heifers, the
J-synch + 400 IU eCG protocol caused follicular codominance and double ovulations
without registering LH surges between 50 and 65 hours after induced luteolysis. | |
