Induction of fertile estrus in bitches using a sustained-release formulation of a GnRH agonist (leuprolide acetate)

Abstract

A single subcutaneous injection of a sustained-release formulation of a potent GnRH agonist, leuprolide acetate (LA; [D-Leu 6,Pro 9NEt]-GnRH), was evaluated as a method of inducing fertile estrus in 12 mature anestrous and 6 prepubertal beagle bitches. The bitches were treated with microencapsulated LA (100 μg/kg, sc) at 120 or 150 d post partum, or at 1 yr of age, followed by a GnRH-analogue (fertirelin; [Pro 9 NEt]-GnRH, 3 μg/kg, im) on the first day of induced estrus. Signs of estrus were seen within 10.3 ± 0.9 d after LA administration in all bitches. The interestrous interval in 120- and 150-d postpartum bitches was shortened (P<0.05) to 191 ± 3 and 222 ± 3 d, respectively, compared with 264 ± 11 d in control bitches. All LA treated dogs demonstrated behavioral estrus and mated. Three of 6 (50%) at 120 d post partum, 6 of 6 (100%) at 150 d post partum and 5 of 6 (83%) of prepubertal (1-yr old) bitches then became pregnant and produced a mean litter size of 4.1 ± 0.8 pups. A normal circulating estrogen and progesterone response pattern was observed in mature anestrous bitches. A prepubertal bitch that failed to become pregnant had a similar estrogen response pattern but an insufficient progesterone profile. The results suggest that microencapsulated LA can be useful in inducing fertile estrus in the domestic dogs.