Influence of unilateral ovariectomy performed before ovulation on ovarian function, steroid hormone levels and development of porcine fetuses

Corpus luteum (CL) activity is closely linked with initiation and maintenance of pregnancy and with fetal development. The present study was aimed to analyze the impact of unilateral ovarian removal on ovarian function, steroid hormone level and fetal distribution and development. Unilateral ovariectomy (uni-OVX) was performed in gilts one day before ovulation (group SHORT, n = 24), 20 days before subsequent ovulation (group LONG, n = 23) or ovaries remained intact (group INTACT, n = 22). Gilts were inseminated by single fixed-time laparoscopic intrauterine insemination (LIUI) after hormonal estrus synchronization. Two days before the end of a 15 day long altrenogest feeding, a part of gilts (n = 23) were surgically fitted with a jugular vein catheter and blood samples were collected to determine of estradiol (E2) and progesterone (P4) concentrations. All animals were slaughtered on day 30 of gestation and ovarian features as well as the number, weight and distribution of fetuses recorded. Altogether, 48 gilts (70%) were pregnant and pregnancy rates did not differ between groups. Short term uni-OVX affected CL number compared to intact and long term OVX gilts (9.9 ± 0.8 vs. 20.6 ± 1.9 and 17.5 ± 0.8; P < 0.05) and the number of fetuses (8.7 ± 0.5 vs. 15.0 ± 1.0 and 14.4 ± 1.1; P<0.05), respectively. Weights of individual CL were not influenced by treatment. Fetuses were differently distributed in the uterine horns after uni-OVX. A higher (P<0.05) proportion of fetuses was present always in the horn which bore the ovary. In all groups, weights of fetuses from uterine horns with an active ovary was similar; however, fetuses of the OVX horn of the SHORT group were lighter (P < 0.05). Steroid hormone profile was typical for pregnant gilts, but differences were observed between groups. Both, the preovulatory E2 concentrations and the early luteal phase P4 levels were higher (P < 0.05) in gilts of the INTACT and LONG groups. In summary, compared to intact gilts, only long term uni-OVX could compensate ovarian development. Short term uni-OVX affects (1) the total number of CL and fetuses, (2) the distribution and weight of fetuses in the uterine horns and (3) steroid hormone levels. Therefore, the time window, but not the uni-OXV per se, which alters the local supply of progesterone, has an impact on fetal development and survival.