1.The Effect of Administration of Different Levels of GnRH on the Day 0, 5 and 12 Post-Insemination on Progesterone Concentration in Dairy Heifers

Abstract

This study was carried out to evaluate the effects of different levels of GnRH in different days of reproductive cycle on progesterone concentration in dairy heifers. Two hundred heifers were divided into ten experimental treatment: control group with no injection (1) administration of 2.5 mL Gonadorelin (a GnRH analogue) in day of insemination (2) administration of 5 mL GnRH in day of insemination (3) administration of 10 mL GnRH in day of AI insemination (4) administration of 2.5 mL GnRH in day 5 post-insemination (5) administration of 5 mL GnRH in day5 post-insemination (6) administration of 10 mL GnRH in day5 post-insemination (7) administration of 2.5 mL GnRH in day 12 post-insemination (8) administration of 5 mL GnRH in day 12 post-insemination (9) administration of 10 mL GnRH in day 12 post-insemination. Blood samples were collected in days 0, 5, 12 and 19 post insemination (AI = Day 0) for analysis of serum P4 concentration. There was no significant difference among experimental groups on day of insemination. Evaluation of P4 concentration on day 19 illustrated differences in progesterone concentration between groups on day 19 post-insemination. P4 concentration of serum in the day 19 post-insemination significantly increased in groups either by 5 or 10 mL injection of GnRH whether in day 5 or 12 post-insemination versus control group (9.24 +/- 2.2, 8.6 +/- 1.96, 9.43 +/- 2.15 and 9.42 +/- 2.14 versus 5.5 +/- 0.8, respectively; p < 0.05). GnRH administration in the day 5 and 12 post-AI significantly increased progesterone concentration that may decline early embryonic death and improve pregnancy rate.