The influence of corpus luteum and first-wave dominant follicle location on conception rate after artificial insemination in Holstein cattle.

The influence of post-ovulatory corpus luteum (CL) and first-wave dominant follicle (1DF) location on pregnancy establishment in cattle remains controversial. This study aimed to reveal the relationship between CL and 1DF positioning, pregnancy outcomes, and blood steroid hormone levels following artificial insemination (AI) in Holstein cattle. Data from heifers (n = 163) and cows (n = 69) with optimally timed AI, defined as ovulation within 24 h post-AI, were analyzed to determine associations between CL (left/right ovary) and 1DF (ipsilateral/contralateral to CL) locations and conception rates. Plasma progesterone (P4) and estradiol-17β (E2) concentrations were measured five days post-insemination. In heifers, neither CL (p = 0.24) nor 1DF location (p = 0.44) affected conception rates. Cows with left-sided CL tended to have higher conception rates than those with right-sided CL (p = 0.08). Relative 1DF location did not affect conception in cows. The location of CL and 1DF did not affect plasma P4 and E2 concentrations or the ratio of plasma E2 to P4 in heifers or cows. These findings suggest a trend towards improved conception rates in cows with CL located on the left ovary post-AI, regardless of 1DF location. The mechanism should not be associated with systemic ovarian hormones.