Effects of human chorionic gonadotropin treatment after artificial inseminations on conception rate with the first follicular wave dominant follicle in the ovary ipsilateral to the corpus luteum in lactating dairy cows

Abstract

We examined the effect of human chorionic gonadotropin (hCG) treatment 5 days after artificial insemination (AI) on conception rate when the first-wave dominant follicle (DF) in the ovaries was either ipsilateral or contralateral to the corpus luteum (CL) in lactating dairy cows. 577 cows from 4 dairy farms were divided into the following two groups 5 days after AI using transrectal ultrasonography: (1) the ipsilateral group (IG; n = 348), in which the DF was ipsilateral to the CL, and (2) the contralateral group (CG; n = 229), in which the DF was contralateral to the CL. IG and CG were further subdivided into two groups: non-treatment groups, which received no treatment (IG, n = 220; CG, n = 128), and hCG treatment group, that was administrated 1500 IU hCG 5 days after AI (IG, n = 143; CG, n = 86). Pregnancy was diagnosed by rectal palpation or transrectal ultrasonography from 53 to 67 days after AI. Conception rate was significantly (P < 0.01) higher in the hCG treatment group of IG (40.6%) than in the non-treatment group of IG (21.4%); however, there was no difference in the non-treatment (51.7%) and hCG treatment (43.0%) groups of CG. Parity, farm, days in milk at AI, interaction between the farm and hCG treatment and interaction between the farm and location of the first-wave DF and CL did not affect conception rate. Our results suggest that conception rate can be improved by administrating hCG only to cows with the first wave DF ipsilateral to the CL.

Keywords: Conception rate; Corpus luteum; Cow; First follicular wave dominant follicle; Human chorionic gonadotropin (hCG).

Fig. 1.

Schematic diagram of the experimental model. The day of artificial insemination (AI) was defined as Day 0. In all of the lactating dairy cows, the position of the first follicular wave dominant follicle (the first-wave DF) and corpus luteum (CL) was confirmed at Day 5 using ultrasonography. hCG (1500 IU) was treated to hCG treatment group on Day 5. Accessory CL, which was formed after ovulation of the first-wave DF, was confirmed on Day 13 using ultrasonography only at Farm D. Pregnancy diagnosis was performed on Day 53–67 by rectal palpation or trans-rectal ultrasonography.