Development of a porcine follicle-stimulating hormone and porcine luteinizing hormone induced ovulation protocol in the seasonally anoestrus brushtail possum (Trichosurus vulpecula)

Abstract

Monovulatory brushtail possums (Trichosurus vulpecula) were stimulated with exogenous hormones during seasonal anoestrus to overcome ovarian insensitivity and induce ovulation. Seasonal ovarian insensitivity to pregnant mare serum gonadotrophin (PMSG) was overcome by a new porcine follicle-stimulating hormone/porcine luteinizing hormone (pFSH/pLH) protocol. This protocol was refined because the original treatment produced oocytes with abnormal morphology. Possums (n = 12 per group) received eight injections of pFSH of 1.5, 3.0 or 6.0 mg per injection (at 12-h intervals for 4 consecutive days). Ovulation was induced 12 h after the final pFSH injection with a 4-mg injection of pLH. Control animals were treated with the established protocol of a single injection of 15 IU of PMSG, followed 48 h later with an injection of 4 mg of pLH. All females responded to pFSH/pLH treatment, although optimal stimulation occurred in those receiving 8 × 3 mg pFSH, with 13–14 ovulations and recovery of 11–12 oocytes per female (8 × 1.5 mg pFSH: 13 ovulations, 8–9 oocytes; 8 × 6 mg pFSH: 7–8 ovulations, 4–5 oocytes). In contrast, only seven of 12 females responded to PMSG/pLH and, of those responding, only 2–3 ovulations occurred and only 1–2 oocytes per female were recovered. However, around 80% of oocytes recovered after PMSG/pLH treatment had undergone nuclear maturation (metaphase II/1st polar body) compared with around 60% of oocytes from pFSH/pLH-treated animals. In possums killed from 27 to 39 h after pLH treatment, ovulation onset was first observed from 30 h and by 31.5 h, all animals had completed ovulation. Laparoscopic artificial insemination (LAI) was performed on pFSH/pLH-treated animals to determine whether the oocytes produced were capable of fertilization. Uterine LAI performed 27.5–28.5 h after pLH treatment yielded 11/26 fertilized oocytes (up to 4-cell stage), whereas vaginal LAI performed 13–14 h after pLH treatment yielded 21/53 fertilized oocytes. A proportion of oocytes generated from the refined pFSH/pLH protocol are thus properly mature and capable of fertilization. Further refinement of the protocol is now needed to improve the yield of fully matured oocytes.