Effect Of GnRH Administration At Day 5 Or Day 7 After AI On Progesterone Concentrations, Corpus Luteum Volume And Pregnancy In Lactating Dairy Cows

Abstract

The objective of the study was to determine the effect of gonadotropin releasing hormone (GnRH) administration on day 5 or day 7 after artificial insemination (AI) on progesterone concentration, total corpus luteum (CL) volume and pregnancy/AI (P/AI) in lactating dairy cows. Multiparous dairy cows (n=1054) from two dairy farms, one in Virginia and one in North Carolina, were enrolled in this study. All cows were synchronized with Presynch-CO-Synch protocol for first service. Following AI (day 0), cows were randomly allocated to one of the following three treatment groups: cows in the GnRH- 5 group (n=335) received 100 μg of GnRH im five days after insemination; cows in the GnRH-7 group (n=390) received 100 μg of GnRH im seven days after insemination and cows in the control group (n=329) received no treatment. Blood samples were collected from a subset of cows (n=52) at day -38, day -24, day -10, day 0 (day of AI) and day 14 for progesterone concentration determination. The progesterone concentrations at day -38, -28, and -10 determined ovarian cyclicity of the cows and the progesterone concentration at day14 (9 or 7 days following GnRH treatment) were used to detect differences in progesterone among treatment groups. The ovaries of the subset of cows were screened using ultrasonography for the formation of accessory CL and total volume of CLs (primary + accessory CLs) was recorded. Cows were examined for pregnancy by transrectal ultrasonography at 30 days and again at 60 days after insemination. The P/AI for GnRH-5, GnRH-7 and control groups were 31.6% (106/335), 33.8% (132/390) and 31.9% (105/329), respectively (p > 0.1). The total CL volume differed among the treatment groups (p < 0.05) but day 14 progesterone concentration did not differ among the treatment groups (p > 0.1). The progesterone concentration in the control group (n=17) was 5.9 ± 0.3 ng/ mL and total CL volume was 8.3 ± 0.6 cm3. The progesterone concentration in the GnRH-5 group (n=15) was 6.3 ± 0.4 ng/ mL and total CL volume was 12.6 ± 0.7 cm3. The progesterone concentration in the GnRH-7 group (n=20) was 6.6 ± 0.4 ng/ mL and total CL volume was 12.0 ± 0.8 cm3. In conclusion, GnRH administration at day 5 or day 7 following insemination neither increased progesterone concentrations nor improved P/AI compared to controls.