Correlated changes in reproductive components accompanying 10 generations of selection for improved sow productivity index.

Reproductive components were compared between a line of sows selected (S) for improved sow productivity index (SPI = 6.5 x number born alive + adjusted 21-d litter weight) and sows from an unselected control (C) line. Generation 9 and 10, second-parity, Landrace sows were chosen from both the S (n = 35) and C (n = 33) line. Sows were slaughtered at a commercial slaughter plant at approximately 75 d of gestation and their reproductive tracts were recovered. Reproductive tracts were evaluated for uterine weight (UTWT), uterine horn length (UTLN), ovulation rate (OR), number of fully formed fetuses (NF), number of mummified fetuses (NM), percentage of fetal survival (FS = NF/OR), fetal space (FSPACE = UTLN/[NF + NM]), and fetal position, sex, and weight. Select-line sows had greater NF (P less than .10) and higher FS (P less than .10) than C-line sows. Select-line sows had longer (P less than .05), and heavier (P less than .01) uteri than C-line sows. However, uterine length adjusted for NF was not different between the two lines. Uterine weight adjusted for NF was greater in S-line sows (P less than .05). Select-line sows had greater total fetal weight (TFWT) (P less than .05) than did C-line sows. Female fetuses positioned between two male fetuses were lighter in weight than all other female fetuses (P less than .01). Male fetuses positioned between two female fetuses did not differ in weight from all other male fetuses.(ABSTRACT TRUNCATED AT 250 WORDS)