Surgical alteration of uterine space influences embryonic loss and fetal growth in the contemporary pig.

BACKGROUND

Litter size is a key economic trait in the swine industry, and ongoing selection for this trait has increased ovulation rates without producing a corresponding increase in uterine capacity. Overcrowding, intensifies competition between fetuses, increasing within-litter variation and the occurrence of intrauterine growth restriction (IUGR).

METHODS

We utilized a combination of unilateral oviductal ligation (UOL) and unilateral hysterectomy-ovariectomy (UHO), to create apposing biological extremes of intrauterine crowding. A total of twenty gilts including N = 7 UHO, N = 7 UOL and N = 6 unaltered controls (CON) were synchronized and bred via artificial insemination. Embryonic loss and fetal viability were evaluated on gestation day 95. The fetal population intensively phenotyped including morphometric assessment of skull shape.

RESULTS

As expected, UOL significantly reduced litter size, but increased embryonic survival, fetal viability, body weight and uniformity compared to CON. In contrast, UHO significantly increased early embryonic loss, but did not alter fetal viability, body weight or uniformity within litter. UOL increased the absolute weight of all organs compared to UHO and CON, with the exception of the brain (BRN) resulting in a significant reduction in BRN consistent with the established brain-sparing effect. The ratio of skull curve-to-linear length (C: L) was significantly reduced in UOL fetuses and found to be strongly correlated with brain-to-liver weight ratio (BRN: LVR).

CONCLUSIONS

The results of this study confirm the negative effects of uterine crowding on fetal growth. They further suggest that contemporary gilts approach the limit of uterine capacity, such that increased crowding results in additional early embryonic loss.