Increased Number of Corpora Lutea by Creating Additional Corpus Luteum Leads to Enhanced Progesterone Concentrations and Improved Fertility in Bovine Repeat-breeder Females Undergoing the Short-term Fixed-time Artificial Insemination Protocol

Background: Lower concentrations of endogenous progesterone (P) after fertilization, due to corpus luteum (CL) dysfunction, leads to an increased embryonic loss and reduced pregnancy outcomes not only in female cattle but also in women. Therefore, an increase in the number of corpora lutea (CLs) may improve fertility in infertile bovine females. The aim of the current study was to investigate the influence of increased number of CLs by creating accessory CL on plasma P concentration and fertility in bovine repeat-breeder females undergoing the short-term fixed-time artificial insemination (FTAI) protocol.Methods: In experiment 1, 32 female cattle had induced ovulation with the short-term (5-day) P-based protocol. To induce additional CL, cows were treated with gonadotropin releasing hormone (GnRH) on day 5 post-induction. On day 14, only female cattle with at least one CL on their ovaries were classified into two groups: 1CL (original CL; n = 14) and 2CLs groups (original CL + accessory CL; n = 8). In experiment 2, 213 bovine repeat-breeder females were bred using the short-term FTAI protocol. On day 5 post-FTAI, cows were divided into two groups: treatment with (GnRH5-treated group; n = 113) or without (GnRH5-untreated group; n = 100) GnRH. On day 14 post-FTAI, cows were sub-divided into two groups: 1CL (n = 115) and 2CLs (n = 39) groups.Results: In experiment 1, the ovarian luteal diameter, area, and volume per total CLs were greater in 2CLs group compared with 1CL group (P < 0.001). On days 12 and 14 post-induction, female cattle bearing two CLs had greater P concentrations than female cattle bearing only one CL on their ovaries (P < 0.05). In experiment 2, CL number and pregnancy rates were greater in GnRH5-treated group compared with GnRH5-untreated group (P < 0.01). Pregnancy rates were greater in 2CLs cows compared with 1CL cows (P < 0.01). Moreover, female cattle bearing two CLs had a greater likelihood of pregnancy (odds ratio = 20.86) than female cattle bearing only one CL on their ovaries (P = 0.001). Conclusions: In bovine model, our findings confirmed a beneficial effect of an additional CL on ovarian hormone and fertility in infertile female cattle. The results highlighted that increased number of CLs by creating additional CL leads to enhanced peripheral P concentrations and improved pregnancy outcomes in bovine repeat-breeder females undergoing the short-term FTAI protocol.