Subclinical Endometritis-Associated Suprabasal Progesterone and Reproductive Dysfunction in Repeat Breeder Crossbred Cows.

Subclinical endometritis (SCE) is common in repeat-breeder cows. This study investigated 99 spontaneous consecutive oestrous cycles (pretreatment [C-1], culture-sensitive antibiotic treatment [C-2], and post-treatment [C-3]) in 33 SCE-positive repeat breeders Jersey crossbred cows (out of 43 screened). Clinico-gynaecological (uterine tone, genital discharge, preovulatory follicle, and corpus luteum [CL]), oestrus, and endocrine determinants were compared between C-1 and C-3. Cows were inseminated up to thrice from C-3. A considerable proportion of SCE cows manifested suprabasal P4 concentrations at C-1 oestrus. Therefore, apart from overall C-1 versus C-3 comparisons, the normal (NP4, n = 15) and suprabasal (SBP4, n = 18) groups were also compared within and between cycles. The prevalence of SCE was 76.74%, with 96.97% of these bacteria-positive at C-1 oestrus. The overall comparisons indicated significantly increased discharge consistency and uterine tone, decreased bacterial load, oestrus onset to ovulation interval, and oestrus duration, and increased preovulatory follicle size, oestradiol (E2), and luteinizing hormone (LH), in C-3. Also, P4 concentrations in the SBP4 group at C-1 oestrus (0.81 ± 0.07 ng/mL) declined significantly at C-3 oestrus (0.44 ± 0.07 ng/mL). Nonetheless, compared with NP4, SBP4 had significantly lesser uterine tone (C-3), E2, and LH (C-1 and C-3), and greater bacterial load (C-1) (within-cycle effects), as well as a decreased oestrus onset-to-ovulation interval and oestrus duration and increased E2 at C-3 (between-cycle effects). The overall pregnancy rate was 75.8%, which had no relation with bacterial presence or load at C-3. In conclusion, suprabasal P4 largely accompanied SCE, intriguingly exhibited more reproductive derangements, and resolved after antibiotic therapy targeted against SCE.