Effect of naloxone, nalbuphine, progesterone and pregnant mare's serum gonadotrophin on the sexual behaviour of ewes
Fuentes, V.O.
Veterinary Record 124(11): 274-276
1989
ISSN/ISBN: 0042-4900 PMID: 2523615 Document Number: 345993
Sheep were medicated with progestogen sponges, pregnant mare's serum gonadotropin, naloxone or nalbuphine during April, May, June or September 1986. It was observed that when suckling ewes were treated three or five weeks after parturition with 45 mg medroxyprogesterone acetate (incorporated in an intravaginal sponge) for 12 days followed by 500 IU of pregnant mare's serum gonadotropin and 0.4 mg naloxone administered intramuscularly after the withdrawal of the sponge, oestrus became evident 24 to 48 hours after the sponges were withdrawn. However, when the naloxone was replaced by 10 mg nalbuphine administered intramuscularly, oestrus was not shown. When the ewes were medicated with the same combination of drugs during anoestrus, the result was similar to that observed during lactation and oestrus was displayed only in the ewes that received naloxone. Thus the opioid antagonist naloxone facilitates the expression of oestrus in the ewe during anoestrus and lactation.