Exogenous application of GnRH after fixed-time artificial insemination (FTAI) and its effect on serum progesterone levels and pregnancy rate in primiparous dairy cows at high altitude environments

Abstract

The aim of the present study was to determine the effect of the exogenous application of gonadotropin-releasing hormone (GnRH) on day 4, 8 and 12 after fixed-time artificial insemination (post-FTAI) in order to evaluate its influence on serum progesterone (P4) levels and pregnancy rate in primiparous dairy cows maintained at high altitude environments. Four experimental groups (Control-T1, T2, T3 and T4) of Holstein Friesian primiparous dairy cows were used. A single dose of GnRH (day-4 (T2), day-8 (T3) and day-12 (T4)) was applied postFTAI. Before and after each treatment, blood samples were collected from the different experimental groups to determine P4 serum levels. Statistically significant differences were observed in serum P4 levels when T1 / T2 were compared to T3 and T4, noting also statistically significant differences between these two treatments (p<0.05). Moreover, statistically significant differences were observed in pregnancy rates when T1 / T2 / T4 were compared to T3 treatment (20% higher) (p<0.05). In conclusion, the exogenous application of GnRH post-FTAI had a significant influence on serum P4 levels (T3) in primiparous dairy cows at high altitude environments. In addition, the pregnancy rate was significantly higher when exogenous GnRH was applied on day-8 (T3) post-FTAI, being possible to optimise FTAI protocols combined with hormonal treatments post-FTAI, and improving fertility in primiparous dairy cows at high altitude environments.

Keywords

• GnRH
• TAI
• progesterone
• high altitude
• fertility
• bovine