Increased luteal tissues after secondary corpus luteum formation leads to enhanced progesterone concentrations and improved fertility in repeat-breeder dairy cows during heat stress condition in tropical climate.

Relatively, little is known about the corpus luteum (CL) function in early pregnancy after the successful treatment of luteal phase deficiency in repeat-breeder dairy cows when exposed to extreme environments under tropical climate. To investigate the influence of increased tissues of corpora lutea (CLs) by inducing secondary CL based on progesterone (P4) concentration and fertility in repeat-breeder dairy cows undergoing the fixed-time artificial insemination (FTAI) protocol, 32 cows were treated with gonadotropin releasing hormone (GnRH) on day 5 post-induction (experiment 1). In experiment 2, 213 cows were bred using the short-term FTAI protocol. On day 5 post-FTAI, cows were divided into two groups: treatment with (GnRH5-treated group) or without (GnRH5-untreated group) GnRH. The temperature-humidity index ranged from 77.3 to 82.8. Cows bearing two CLs had greater P4 concentrations than cows bearing only one CL on their ovaries (P < 0.05). Pregnancy rates were greater in GnRH5-treated group than the GnRH5-untreated group (P < 0.01). Moreover, repeat-breeder cows bearing two CLs had a greater likelihood of pregnancy (odds ratio = 20.86) than cows bearing only one CL on their ovaries (P < 0.01). Under heat stress condition, the results highlighted that increasing luteal tissues by creating secondary CL leads to enhanced peripheral P4 concentrations and improved pregnancy outcomes in repeat-breeder dairy cows.

Uterine artery flow velocity waveform, arterial flow indices, follicular dynamics, and sex hormones during preovulatory period in synchronized ovulatory cycle of Bos indicus beef cows.

A greater understanding of the uterine artery's (UtA) biology is essential to the increase in female reproductive abilities. The UtA flow velocity waveform, blood flow volume (BFV), pulsatility and resistance indices (PI and RI), blood flow velocities, dynamics of the dominant follicle (DF), and estradiol (E2) and progesterone (P4) levels in an induced ovulatory cycle were evaluated in Thai native cattle. Twenty cows were induced with synchronized ovulation through a P4-releasing device, from Day -9 to Day -4, concurrent with the administration of two doses of a gonadotropin-releasing hormone on Day -9 and Day -1, and two doses of prostaglandin F2α on Day -4 and 8 h later. Day 0 was designated as the day of ovulation. The cows underwent Doppler sonographic determination and blood collection from Day -4 to Day 0. The cows were classified in the non-ovulating (n = 5) and ovulating groups (n = 15). The ovulating cows presented higher BFV values, blood flow velocities, DF growth rates, and E2 levels; yet lower PI values and P4 concentrations, than those of the non-ovulating cows. The BFV values and the blood flow velocities were greater, but the RI and PI values were lower in the ovulatory side UtA than in the contraovulatory side UtA. The BFV values were positively correlated with blood flow velocities, DF growth rates and E2 concentrations in the ovulating cows; confirming the importance of UtA blood flow, follicular growth, and E2-vasodilation during preovulatory phase in the induced ovulatory cycle of Bos indicus beef cows.