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Allelic variation in the secreted folate binding protein gene is associated with uterine capacity in swine¹

ARS, USDA, Roman L. Hruska U.S. Meat Animal Research Center, Clay Center, NE 68933

² Correspondence: P.O. Box 166, State Spur 18D (phone: 402-762-4187; fax: 402-762-4382; e-mail: vallet{at}email.marc.usda.gov).

Previous comparisons between the cDNA and gene sequences for secreted folate binding protein (sFBP) indicated a 12-bp insertion/deletion (ins/del) polymorphism in exon 1 and a SNP that altered (Ser-Arg) the protein AA sequence. The effect of the Ser-Arg SNP on reproductive traits was examined in three groups of Meishan-White European breed crossbred gilts. The gilts for all three groups were unilaterally hysterectomized-ovariectomized (UHO) at 100 d of age. Group 1 gilts (n = 77) were mated at estrus, slaughtered at d 105 of pregnancy, and a blood sample was collected from each fetus to determine fetal hematocrit. The number of corpora lutea and fetuses and the fetal and placental weights were recorded. Group 2 gilts (n = 46) were mated, the remaining uterine horn was flushed with 20 mL of saline on d 11 of pregnancy, conceptuses were counted, and flushings were measured for total sFBP. Gilts were allowed an estrous cycle to recover, mated again at estrus, slaughtered at 105 d of gestation, and the data as described for Group 1 were collected. Groups 1 and 2 gilts were genotyped for the Ser-Arg SNP. In Group 3, gilts (n = 70) and boars (n = 30) were genotyped for the Ser-Arg SNP before mating, and like genotypes were mated. Gilts were then treated as described for Group 2. The effect of the 12-bp ins/del on reproductive traits was examined in 407 white crossbred UHO gilts from a randomly selected control line and from lines selected for ovulation rate (OR) and uterine capacity (UC). Gilts were mated and slaughtered at 105 d of age, and the numbers of corpora lutea and live fetuses, and fetal and placental weights and fetal hematocrits were recorded. The 12-bp ins/del also was evaluated in 131 intact gilts from the OR selected line. These gilts were mated at approximately 250 d of age and farrowed. The numbers of fully formed and live piglets were recorded. A significant effect (P < 0.05) of the Ser-Arg SNP was detected on the number of embryos present on d 11 of pregnancy and on UC. The sFBP 12-bp ins/del was associated with UC (P < 0.01) and the number of CL (P < 0.05) in UHO gilts, but not with litter size in intact gilts from the OR line. Results suggest that the 12-bp ins/del polymorphism could be exploited to increase litter size in swine, provided that the negative effect of the polymorphism on OR is overcome.

Key Words: Embryo • Erythropoiesis • Fetus • Folate • Pregnancy • Swine