175 SAVING PREGNANCIES IN BEEF CATTLE AFTER A LUTEOLYTIC DOSE OF PROSTAGLANDIN

Abstract

Three experiments were conducted to determine if pregnancy (PREG) could be maintained in cattle after receiving a luteolytic dose of PGF2α (PGF) (25 mg, Lutalyse) i.m. during 30 to 40 d or 80 to 90 d of gestation (GEST). The objectives were to determine whether PREG could be maintained in the absence of a functional CL with administration (ADM) of progesterone (P4) or altrenogest (ALT) following PGF injection and to determine if induced luteal tissue (LT) could support the PREG to term. In Exp I, crossbred cows (BCS = 5 to 7) 30 to 40 d of (GEST) were randomly assigned to receive 100 mg of P4 in 3 mL of vehicle s.c. at 2 h post-PGF (p-PGF) (Trt A; n = 2), 6 h p-PGF (Trt B; n = 3), 10 h p-PGF (Trt C; n = 3), 14 h p-PGF (Trt D; n = 2) or 18 h p-PGF (Trt E; n = 2). After PGF, all cows were given 100 mg P4 daily i.m. for ≥7 d. PREG was maintained in 100%, 100%, 67%, 50% and 0% of the females in Trts A, B, C, D and E, respectively. Following the 7-d P4 Trt, 3 cows were selected from the remaining PREG females for induction of LT. These cows were evaluated via ultrasound 2 to 3 times weekly until a follicle ≥10 mm developed on the ovary ipsilateral to the gravid horn. At that time, 2500 IU of hCG were given i.m. to induce LT development. LT developed successfully in 2 of 3 (67%) females at which time the P4 was decreased over 10 d. One cow lost her PREG prior to LT formation, 13 d p-PGF. Of the 2 remaining females with induced LT, 1 female lost the PREG at 60 d post-P4 Trt and the remaining female gave birth to a healthy calf at 286 d of PREG, without dystocia. In Exp II, similar beef cows (BCS = 5 to 7) at 80 to 90 d of GEST were randomly assigned to receive a dose of 100 mg ALT (drenching) starting at 2 h p-PGF (Trt A; n = 3), 6 h p-PGF (Trt B; n = 2) or 12 h p-PGF (Trt C; n = 2). At 24 h after ALT Trt, all cows received two 15-mg norgestomet implants to maintain PREG. One female, in Trt B, did not respond to PGF and was removed from the study. PREG was maintained in 67%, 100% and 0% of the females in Trt A, B and C, respectively. From the remaining 3 PREG cows, 2 were selected for induction of LT, as described above. Both cows formed induced LT and 14 d later both implants were removed. To date, both females have maintained their PREG and are expected to calve in 30 d. In Exp III, crossbred heifers (BCS = 5 to 6) at 30 to 40 d of gestation were randomly assigned to receive 100 mg ALT 6 h p-PGF (Trt A; n = 3), 12 h p-PGF (Trt B; n = 2) or 18 h p-PGF (Trt C; n = 2). PREG was maintained in 100% of females. Subsequently, induction of LT was attempted in all 7 females. To date, 5 females have induced LT. Of the remaining 2 females, 1 lost her PREG at 80 d of GEST, while the other female is currently in the process of developing fresh LT. These results demonstrate that PREG can be maintained with P4 or ALT administration following a PGF injection, and that induced luteal tissue can support these PREG to term, thus eliminating frequent ADM of progestin in an attempt to maintain a viable PREG. To our knowledge, this is the first report of a pregnancy developing to term, resulting in normal parturition and a viable calf following induced luteal tissue in the absence of the initial CL of PREG.