Induction of ovulation in the acyclic postpartum ewe following continuous, low-dose subcutaneous infusion of GnRH

• Published in: Theriogenology Vol. 43; no. 6; pp. 1019 - 1030
• Main Authors: Fray, M.D., Lamming, G.E., Haresign, W.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15-04-1995
• Subjects: BREBIS; CICLO ESTRAL; CYCLE OESTRAL; EPOCA DE APAREAMIENTO; ESTERILIDAD FEMENINA; ewe; GLANDULA PITUITARIA; GnRH; GONADOLIBERINE; HORMONA LIBERADORA DE GONADOTROPINA; HORMONAS; HORMONE; HYPOPHYSE; INFERTILITE FEMELLE; METHODE D'APPLICATION; METODOS DE APLICACION; OVAIRE; OVARIOS; OVEJA; OVULACION; OVULATION; PLASMA SANGUIN; PLASMA SANGUINEO; postpartum; PROGESTAGENE; PROGESTAGENOS; PROGESTERONA; PROGESTERONE; PUERPERIO; PUERPERIUM; SAISON D'ACCOUPLEMENT; SECRECION; SECRETION; postpartum; ewe; GnRH; ovulation
• ISSN: 0093-691X; 1879-3231
• DOI: 10.1016/0093-691X(95)00066-H

Pituitary and ovarian responses to subcutaneous infusion of GnRH were investigated in acyclic, lactating Mule ewes during the breeding season. Thirty postpartum ewes were split into 3 equal groups; Group G received GnRH (250 ng/h) for 96 h; Group P + G was primed with progestagen for 10 d then received GnRH (250 ng/h) for 96 h; and Group P received progestagen priming and saline vehicle only. The infusions were delivered via osmotic minipumps inserted 26.6 ± 0.45 d post partum (Day 0 of the study). Blood samples were collected for LH analysis every 15 min from 12 h before until 8 h after minipump insertion, then every 2 h for a further 112 h. Daily blood samples were collected for progesterone analysis on Days 1 to 10 following minipump insertion, then every third day for a further 25 d. In addition, the reproductive tract was examined by laparoscopy on Day −5 and Day +7 and estrous behavior was monitored between Day −4 and Day +7.
Progestagen priming suppressed (P < 0.05) plasma LH levels (0.27 ± 0.03 vs 0.46 ± 0.06 ng/ml) during the preinfusion period, but the GnRH-induced LH release was similar for Group G and Group P + G. The LH surge began significantly (P < 0.05) earlier (32.0 ± 3.0 vs 56.3 ± 4.1 h)and was of greater magnitude(32.15 ± 3.56vs 18.84 ± 4.13 ng/ml) in the unprimed than the primed ewes. None of the ewes infused with saline produced a preovulatory LH surge. The GnRH infusion induced ovulation in 10/10 unprimed and 7/9 progestagen-primed ewes, with no significant difference in ovulation rate (1.78 ± 0.15 and 1.33 ± 0.21, respectively). Ovulation was followed by normal luteal function in 4/10 Group-G ewes, while the remaining 6 ewes had short luteal phases. In contrast, each of the 7 Group-P + G ewes that ovulated secreted progesterone for at least 10 d, although elevated plasma progesterone levels were maintained in 3/7 unmated ewes for >35 d. Throughout the study only 2 ewes (both from Group P + G) displayed estrus. These data demonstrate that although a low dose, continuous infusion of GnRH can increase tonic LH concentrations sufficient to promote a preovulatory LH surge and induce ovulation, behavioral estrus and normal luteal function do not consistently follow ovulation in the progestagen-primed, postpartum ewe.