Relaxin on induction of parturition in cattle: effects on hormonal, pelvic and cervical changes, and postpartum fertility
The effects of purified porcine relaxin (RLX, 3,000 U/mg) on induction of parturition, progesterone, estrogens, and relaxin profiles, cervical dilatation and the patterns of pelvic development in three genetically selected frame sizes of primiparous beef heifers during late pregnancy were studied. RLX (n = 39), with cloprostenol (Clo) or dexamethasone (Dex, n = 51), Clo or Dex (n = 20), and vehicle treated (n = 16) was administered. Relaxin induces marked cervical dilatation within a few hours and different patterns of pelvic development in beef heifers of different body frame sizes due to significant increases in pelvic height and width. In combination with Clo or Dex, relaxin similarly induces significant increases in pelvic area and cervical dilatation within 24 h. Intracervical administration of relaxin on Day 277-278 induces highly significant earlier calving (2.0, 2.5 and 5.3 days for relaxin-single, relaxin-double, and PBS-gel vehicle). In combination with Clo or Dex, relaxin significantly reduced the interval between treatment and calving (33 vs. 55 h). The shifts in progesterone, estrone and 17(beta)-estradiol secretion reflect premature parturition induced by relaxin or relaxin with Clo or Dex in cattle. Relaxin administered either in the cervical os or intramuscularly induces a highly significant decrease in progesterone secretion within 90 minutes, and a subsequent increase in blood levels of 17(beta)-estradiol and estrone independent of parturition. Immunoreactive relaxin in peripheral blood of heifers, as based on a porcine relaxin standard for radioimmunoassay, indicates concentrations of <0.5 ng/ml during late pregnancy. Relaxin combined with Clo or Dex significantly reduced the incidence of retained placenta beyond 24 h (23 vs. 75%) as well as the duration of retention of placenta (12 vs. 24 h), reduced the duration of labor (2.0 vs. 3.6 h), increased calving ease (62 vs. 35%), and reduced mean dystocia score (1.8 vs. 2.6). The increased pelvic area resulted in decreased incidence and severity of dystocia and incidence and duration of retained placenta. Postpartum conception rates were not adversely affected by relaxin.