Hormones

The general principals that allow the manipulation of the reproductive physiology of the sheep are discussed in detail in Note 2.

2.2.1. Follicle Stimulation and Superovulation

2.2.1.1. Pituitary Follicle Stimulating Hormone (FSH)

Preparations of FSH derived from pituitary glands of pig or sheep or the urine of postmenopausal women are available. These preparations usually are costly, have little luteinizing hormone (LH) contamination, and, because of their short half-life, need to be injected twice daily over a period of 3-A d. Although they are very successful in producing embryos, they may be less attractive to users considering the other work inputs needed to produce transgenic sheep. Lesser amounts can be used in a single dose combination with pregnant mares' serum gonadotropin (PMSG), however the final choice should be made in the light of personal experience. Preparations available include: F.S.H.-P. (Burns-Biotec Lab. Inc., Omaha, NE), Folltropin-V®(Vetrepharm Inc., Ontario, Canada), and Ovagen® (Immuno-chemical Products Ltd., Auckland, New Zealand).

This hormone is produced by the endometrial cups of the pregnant mare and stimulates the secondary wave of ovulations around 40-120 d of gestation. It is extracted from blood serum for use as an FSH-like hormone and contains partially purified fractions of an FSH-like glycoprotein. The half-life of this material is long and care must be taken not to use excessive amounts, because follicular development and estradiol secretion will continue after ovulation. With excessive numbers of ovulations, this may lead to problems with sperm transport, fimbrial recovery of eggs, and egg transport through the oviduct, resulting in low yields of eggs and low fertilization rates. Properly used, however, PMSG preparations are a cheap and efficient means of increasing ovulation rate (OR) to satisfactory levels. Intrauterine insemination must be used in conjunction with progestagen pessaries and PMSG to negate the problems of defective sperm transport, to give control over insemination time, and to ensure that fertilization takes place. Preparations used in this laboratory are: Folligon® (Intervet International B.V., Boxmeer, Holland) and Pregnecol® (Heriot Agvet Pty Ltd., Ferntree Gully, Victoria, Australia).

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