EFFECTS OF PORCINE RELAXIN ON INDUCED PARTURITION IN BEEF HEIFERS

Two-year-old crossbred beef heifers were used to test the effects of p orcine relaxin (pRelaxin) alone, or in combination with dexamethasone, on the induction of parturition, the incidence of dystocia, and retai ned placentas. Effects of treatment on pelvic area, postpartum interva l, milk production, colostrum quality, calf birth weight, calf vigor, and calf performance were also evaluated. On Day 275 of gestation, hei fers from two fetal-sire groups were randomly assigned to one of four groups in a 2 x 2 factorial design and received: no treatment (control s, n = 19), 20 mg of dexamethasone intramuscularly (im) (n = 22), 5 mg of pRelaxin (3,000 U/mg) im (n = 19), or 20 mg of dexamethasone plus 5 mg of pRelaxin (n = 17). Length of gestation (in days) was less (P < 0.05) in heifers treated with dexamethasone (279.8 +/- 1.0) than in c ontrols (286.6 +/- 0.9), but was not influenced (P > 0.05) by treatmen t with pRelaxin. The incidence of retained placentas in heifers treate d only with dexamethasone (27.3%) was not reduced by concomitant treat ment with pRelaxin (35.3%). Retained placentas were not observed in an y control heifers and in only one heifer (5.2%) treated solely with pR elaxin. Ease of calving (1 = unassisted, 5 = abnormal presentation) wa s not influenced by treatment (P > 0.05), even though birth weights (i n kilograms) of calves from heifers treated with dexamethasone (36.4 /- 0.8) were less (P < .01) than those of calves from nondexamethasone -treated heifers (39.2 +/- 0.8). Dexamethasone tended to reduce (P +/- 0.07) calf vigor (1 = healthy and strong, 5 = dead on arrival; 1.48 /- 0.11 vs. 1.18 +/- 0.11), but was not (P > 0.05) influenced by pRela xin. The duration of the postpartum anestrous interval (73.1 +/- 1.8 d across groups) and pelvic areas following treatment and parturition w ere not influenced (P > 0.05) by dexamethasone or pRelaxin. Although d eterminants of colostrum quality (P < 0.01) and quantity (P < 0.08) of milk produced were influenced by dexamethasone, adjusted 205-d weight s of calves did not differ (P > 0.05) among groups. In conclusion, tre atment with pRelaxin alone failed to induce parturition or, when combi ned with dexamethasone, to reduce the incidence of retained placentas. (C) Elsevier Science Inc. 1996