The relationship between accessory corpus luteum maintenance and pregnancy-specific protein B in pregnant Japanese Black cows

抄録

In pregnant cows, regression of accessory corpus luteum (ACL) was more frequently observed in ACL contralateral to the original CL than ACL ipsilateral to the original CL. To investigate the factors related to ACL regression, CL characteristics and plasma pregnancy-specific protein B (PSPB) levels were evaluated in pregnant Japanese Black cows with human chorionic gonadotropin (hCG)-induced ACL formation. The cows were assigned to the control (n=10) or the hCG treatment group (n=50) on the day of embryo transfer (ET) (Day 0 = Estrus; Days 6–8 = Day ET). Cows treated with hCG were divided into: ipsilateral ACL maintenance (ipsi-maint, n = 25), contralateral ACL maintenance (contra-maint, n = 17), and contralateral ACL regression (contra-regr, n = 8). Characteristics of CL and PSPB were evaluated from Days 35 to 63. On Day 35, no difference was observed in the volume and blood flow area of ACL between the contra-maint and contra-regr groups. Plasma progesterone (P₄) concentrations were higher in hCG-treated cows than in untreated cows, regardless of ACL regression. During the experiment, P₄ concentrations decreased in the contra-regr group, while those unchanged in the ipsi-maint, contra-maint, and control groups. Higher PSPB levels were observed in the hCG-treated groups than in the control group. Compared to the ACL maintenance group, delayed PSPB recovery was observed in the contra-regr group. Additionally, PSPB concentration in the ipsi-maint group was greater than that in the contra-maint group. This study provides insights into the relationship between ipsilateral ACL maintenance and PSPB in pregnant cows.