LUTEAL FUNCTION AFTER INTRAUTERINE INFUSION OF RECOMBINANT BOVINE INTERFERON-ALPHA-I1 INTO POSTPARTUM BEEF-COWS EXPECTED TO HAVE SHORT OR NORMAL LUTEAL PHASES

This study was conducted to determine whether intrauterine infusion of recombinant bovine interferon-alpha(I)l (rboIFN-alpha(I)1), which has 70% sequence identity to bovine trophoblast protein-1, will prevent regression of corpora lutea anticipated to have a short lifespan. Twenty-six beef cows in good body condition were allotted to four treatment groups at parturition in a 2 x 2 factorial design. Treatments were: group 1, saline; group 2, rboIFN-alpha(I)1; group 3, norgestomet-saline; and group 4, norgestomet-rboIFN-alpha(I)1. Norgestomet implants were inserted on days 21-24 postpartum and removed 9 days later (before injection of human chorionic gonadotrophin (hCG)). Ovulation was induced 30 to 33 days postpartum with 5000 or 10 000 iu hCG. Groups 1 (n = 7) and 3 (n = 5) were given intrauterine infusions (rectocervical approach) twice daily with saline on days 1-12 or 13-24 after hCG injection, respectively. Cows allotted to groups 2 (n = 8) and 4 (n = 6) were given intrauterine infusions (rectocervical approach) of 2 mg rboIFN-alpha(I)1 twice daily on days 1-12 or 13-24 after hCG injection, respectively. Treatment with both norgestomet and rboIFN-alpha(I)1 delayed (P < 0.01) luteolysis. Lengths of luteal phases (days; mean +/- SEM) were 8.4 +/- 0.7 (group 1, saline), 14.1 +/- 1.0 (group 2, rboIFN-alpha(I)1), 18.6 +/- 1.3 (group 3, norgestomet-saline) and 20.8 +/- 1.2 (group 4, norgestomet-rboIFN-alpha(I)1). Concentration of progesterone in serum was similar among all groups the first 6 days following hCG-induced ovulation, but differed (P < 0.01) thereafter. Mean concentration of progesterone was lower (P < 0.01) in saline-treated cows (group 1) from days 8 to 13 than in cows infused with rboIFN-alpha(I)1 or pretreated with norgestomet. In summary, intrauterine infusion of rboIFN-alpha(I)1 delayed luteolysis of corpora lutea anticipated to have a short lifespan.