Effects of GnRH and hCG administration on conception rate and the subsequent estrous cycle on day 12 following artificial insemination in Holstein cows

The present study investigates the effects of gonadotropin-releasing hormone (GnRH) and human chorionic gonadotropin administration on the conception rate of cows 12 days after artificial insemination (AI). Included in the study were 150 high milkyielding Holstein cows housed under the same husbandry and feeding conditions. All had calved at least once between the ages of 2.5 and 6 years, and were between 90 and 220 days in milk. In accordance with the farm’s reproductive management approach, a controlled internal drug release (CIDR) device was inserted into the vagina concurrent with a GnRH injection (day 0), and the device was removed on day 7. Two prostaglandin F2α (PGF2α) injections were made 24 h apart, and a timed artificial insemination (TAI) procedure was performed in conjunction with a GnRH injection. The animals were randomly assigned to one of three groups 36 h after receiving the second dose of PGF2α. On day 12 following the AI procedure, the first group (GnRH, n = 50) was given GnRH, the second group (hCG, n = 50) was given hCG, and the third group (Control, n = 50) received no additional treatment. Blood samples were collected for progesterone analysis on days 12, 16, and 20 following the AI procedure, and pregnancy testing was initiated on day 30. Pregnancy rates of 46%, 48%, and 42% were recorded in the GnRH, hCG, and Control groups, respectively (p > 0.05), with no significant differences noted between the experimental groups. The animals determined to be pregnant underwent an ultrasound scan on day 60, during which one embryonic death was noted in the Control group (4.7%). The progesterone levels observed in the GnRH and hCG groups on day 16 following AI were considerably greater than the 12th day progesterone levels (p < 0.05; p < 0.01). It was concluded from the study that GnRH and hCG injections on day 12 following AI increase progesterone levels, but have no influence on conception rates.