Endogenous opioid suppression of release of luteinizing hormone during suckling in postpartum anestrous beef cows

  • Myers T
  • Myers D
  • Gregg D
 et al. 
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Beef cows were used to determine if suckling influences release of LH via endogenous opioids at 28 ± 4 d after parturition. Cows of similar weight and body condition (6.8 ± .1, 1=emaciated, 9=obese) were assigned randomly to five groups (n=6 to 7): 1) control-suckled/saline (suckled 15 min every 6 hr for 48 hr); 2) control-suckled/ naloxone; 3) calf-removal/saline (calf removal for 52 hr); 4) calf-removal/naloxone; and 5) control-suckled/GnRH (Gonadotropin-Releasing Hormone). At 0 hr, saline was administered to all cows. This treatment was continued at 6 hr intervals for 24 hr. Either naloxone (0.5 mg/kg), GnRH (40 ng/kg) or saline was administered to cows in their respective groups every 6 hr during the ensuing 24-hr period in calf-removal groups, or immediately preceding each suckling episode in the control-suckled groups. Blood samples for analysis of luteinizing hormone (LH) were collected at 15-min intervals for 1 hr prior to and 3 hr after treatment at 0, 24, 36 and 48 hr. Cows were observed for estrus twice daily. All cows in the control-suckled/GnRH group released LH (P.05) by the control-suckled regime. However, calf-removal alone, or in combination with naloxone, increased (P

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  • T. R. Myers

  • D. A. Myers

  • D. W. Gregg

  • G. E. Moss

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