Sows that fail to become pregnant show luteal regression at day 13 after mating

In mated sows, corpus luteum (CL) function is important for the establishment of the pregnancy. The maximum CL size is established at day 8 - 9 of the pregnancy and maintained autonomous until day 12. Then, CL maintenance will depend on hormones such as LH and PGF2α. PGF2α is released from the endometrium at day 14 and triggers CL regression. This regression can be prevented in pregnant sows due to estradiol production from the attaching conceptuses; which decreases endocrine PGF2α release. We hypothesized that a negative CL development between day 12 and 13 has a negative effect on the pregnancy rate in mated sows and on litter size in pregnant sows.

We performed a transrectal ultrasound examination (10 MHz, linear array probe, SV3513, Esaote SpA, Italy) of both ovaries and their CLs at day 10 (CLarea10) and 13 (CLarea13) after ovulation in 46 mated crossbred sows (Finnish Yorkshire x Finnish Landrace). The ultrasound images were analyzed on the computer using IMPAX 6.5.5 picture archiving and communication system (Agfa Healthcare, Belgium). We measured of each ovary the size (area in cm2) of the five biggest CLs and averaged them. Furthermore, we calculated the difference of the average CL area between day 10 and 13 (CLarea13-10). Pregnancy detection was performed two weeks later and the numbers of alive, still born, and total born piglets were determined at subsequent parturition. We analyzed average CL area per pregnancy status using an independent two sample t-test and relations with litter size using a linear regression model (PASW Statistics v. 18.0.0).

The parity was 3.8 ± 1 (mean ± SD), CLarea10 0.63 ± 0.11 cm², CLarea13 0.65 ± 0.13 cm², and CLarea13-10 0.02 ± 0.12 cm². At 4 weeks after insemination, 40 sows were detected pregnant (PREG) and 6 not pregnant (NONPREG). Pregnancy status at 4 weeks was not related with CLarea10 (PREG 0.62 ± 0.12 cm² vs. NONPREG 0.69 ± 0.07 cm²), but was related with CLarea13 (PREG 0.66 ± 0.11 cm² vs. NONPREG 0.55 ± 0.18 cm²; P = 0.046) and CL13-10 (PREG 0.05 ± 0.08 cm² vs. NONPREG -0.15 ± 0.16 cm²; P < 0.001).No correlations were found between CLarea10, CLarea13, and CLarea13-10 and the number of total, alive, and still born piglets at subsequent farrowing.

The results indicate that there is no difference in the development of the corpus luteum between pregnant and not pregnant sows during the autonomous period. After that period, when the destination of the corpus luteum (CL) starts to be dependent on hormonal interactions, CLs of mated nonpregnant sows decrease in size, resulting in smaller CL at day 13 after ovulation. In pregnant sows, CL size at day 10-13 is not related with subsequent litter size.

Disclosure of Interest: None Declared.