Effect of sperm kinematics and size of follicle at ovulation on pregnancy rate after timed AI of beef cows

The objectives of this study were to evaluate whether the diameter of the preovulatory follicle and the post-thaw sperm kinematics are factors that affect successful establishment of a pregnancy after timed AI (TAI) of postpartum beef cows. Nelore cows (n = 346) were subjected to an estradiol-progesterone based TAI protocol. At TAI, cows were categorized according to the diameter of the preovulatory follicle (POF) in the Early Ovulation (EO group, n = 184), and Late Ovulation (LO group, n = 162) groups. Sperm were classified, according to CASA analysis, as Hyper-activated (H+), and Non-Hyper-activated (H-). The H + and H- semen was used to inseminate cows that were classified to be in the EO and LO groups. Thus, after distribution, the groups were: EOH+ (n = 89), EOH- (n = 95), LOH+ (n = 96), and LOH- (n = 66). Pregnancy per AI (P/AI) was greater (P < 0.05) for EOH+ (66.3%, 59/89), EOH- (65.3%, 62/95), and LOH- (72.7%, 48/66) groups than for LOH + group (52.1%, 50/96). The results of the study indicate that cows with a smaller POF are less likely to become pregnant when insemination is with semen considered as hyper-activated (H+). In contrast, when inseminations are performed with semen categorized to be non-hyper-activated (H-), cows of the EO and LO groups had acceptable and similar pregnancy rates as a result of timed AI.