Gonadotrophins

By | 2011-08-18

Chorionic gonadotrophin (human chorionic gonadotrophin, hCG) is a complex glycoprotein excreted in the urine of women during pregnancy. It has a similar effect to luteinising hormone (LH) secreted by the anterior pituitary gland in both males and females.

In veterinary practice, it is used to supplement or replace luteinising hormone in cases of ovulation failure or delay, or to help control the timing of ovulation. In mares, chorionic gonadotrophin (hCG) is used to induce ovulation in animals with prolonged oestrus during the transitional phase from winter anoestrus to the onset of normal cyclical ovarian activity, and before mating or AI.

In males, chorionic gonadotrophin (hCG) stimulates the secretion of testosterone by interstitial (Leydig) testicular cells. It is used to improve libido, with variable results, and also to identify the presence of a retained testis in cryptorchids.

Detection of a cryptorchid is most frequently employed in horses. Two blood samples are taken: one before and the second 30 to 120 minutes after an injection of chorionic gonadotrophin (6000 units given by intravenous injection). A serum-testosterone concentration greater than 100 pg/mL, a rise in serum-testosterone concentration in response to chorionic gonadotrophin, or preferably both, confirms the presence of testicular tissue. This is known as the hCG stimulation test. It can also be used in other species using a similar regimen but with different dosages (for example 50 units/kg is used in dogs).

Serum gonadotrophin (equine chorionic gonadotrophin, eCG) is also a complex glycoprotein. It is extracted from mares’ serum during the first trimester of pregnancy (but not before 35 to 40 days). The effects of serum gonadotrophin (eCG) in animals most closely resemble those of follicle-stimulating hormone (FSH) secreted by the anterior pituitary gland, but with a much longer duration; it also has some LH-like activity.

Serum gonadotrophin (eCG) is used to advance the onset of follicular growth and ovulation, in combination with progestogen-impregnated intravaginal sponges, in sheep and goats. In general, the earlier the time of the onset of the breeding season is advanced and the lower the normal prolificacy of the flock, the higher the dose of serum gonadotrophin (eCG) required. Therefore it is recommended that accurate flock records are kept including breed, date and dose of drug administered, and lambs produced, so that the drug dose may be adjusted in future seasons to provide optimal results. Serum gonadotrophin (eCG) is sometimes used in conjunction with a progesterone-releasing intravaginal device (Prid) to stimulate cyclical activity in acyclical cows. In combination with chorionic gonadotrophin (hCG), serum gonadotrophin (eCG) can induce oestrus in bitches in anoestrus.

In males, serum gonadotrophin (eCG) promotes spermatogenesis. Individuals may show a variable response to serum gonadotrophin (eCG) and the degree of efficacy is low. Recommended doses are as follows: stallions and bulls 1000 to 3000 units, rams and boars 500 to 700 units, and dogs 400 to 800 units. The drug is administered by intramuscular injection weekly for 4 to 6 weeks.

Serum gonadotrophin (eCG) is administered to induce superovulation in cattle used as donors in embryo transfer. The general procedure is: serum gonadotrophin (eCG) is given once on day 9 to 13 of a normal oestrous cycle. Luteolysis is induced 48 hours later by administration of a prostaglandin F2aplha or analogue, given at 1.5 times the normal dose. Oestrus will be evident within 48 hours. Artificial insemination is carried out at 60 and 72 hours after prostaglandin administration. Embryos are collected 6 to 8 days after insemination and transferred to suitable synchronised recipients either directly or after freezing in liquid nitrogen. The efficacy of this procedure is variable and an exaggerated response may occur due to the long half-life of serum gonadotrophin.

Follicle stimulating hormone is used to induce superovulation. Porcine or ovine follicle stimulating hormone is used for superovulation of cattle, in preference to serum gonadotrophin, because it has a shorter half-life and is less likely to produce an excessive superovulatory response. The super-ovulatory response and the quality of recovered embryos can be influenced by the relative amounts of FSH and LH in the product.

Menotrophin contains human menopausal gonadotrophins extracted from the urine of postmenopausal women. It has both luteinising and follicle-stimulating hormone activity in equal amounts. It is an effective method of inducing super-ovulation.

CHORIONIC GONADOTROPHIN

(Human chorionic gonadotrophin, hCG)

Indications. See under Dose

Warnings. Immune-mediated reduced effect after repeated doses, occasional anaphylactic reactions; ensure that mares are not pregnant before treatment

Dose: See also notes above

Horses: induction of ovulation, by intramuscular or intravenous injection, 1500-3000 units 24 hours before mating or AI

Suboestrus (follicles > 2 cm diameter), by intramuscular or intravenous injection, 1500-3000 units. Repeat after 2 days if required

Cattle: repeated failure of conception, by intramuscular or intravenous injection, 1500 units at mating or AI Cystic ovarian disease, by intravenous injection, 3000 units

Dogs

Females: anoestrus, by intramuscular or intravenous injection, 500 units on first day of oestrus after pretreatment with serum gonadotrophin by subcutaneous injection, 20 units/kg daily for 10 days

Ovulation failure , by intramuscular injection, 100-500 units on day of mating

Delayed ovulation, prolonged pro-oestrus, by intramuscular injection, 100-800 units daily or 20 units/kg until vaginal bleeding ceases. Mate during behavioural oestrus

Males: deficient libido, by intramuscular injection, 100-500 units twice weekly for up to 6 weeks or 6-12 hours before mating (temporary effect)

Prescription-only medicine: Chorulon (Intervet) UK

Injection, powder for reconstitution, chorionic gonadotrophin 1500 units, for horses, cattle, dogs

Withdrawal Periods. Slaughter withdrawal period nil, milk withdrawal period nil

FOLLICLE STIMULATING HORMONE (PORCINE)

Indications. Superovulation in cattle

Warnings. Immune-mediated reduced effect after repeated doses, occasional anaphylactic reactions

Dose: See preparation details

Prescription-only medicine: Super-Ov (Global Genetics) UK

Injection, powder for reconstitution, follicle stimulating hormone (porcine) 75 units, for cattle

Withdrawal Periods.

Cattle: slaughter 28 days, milk should not be taken for human consumption within 24 hours of embryo collection

Dose:

Cattle: by intramuscular injection, 25 units daily for 3 days. Prostaglandin F2alpha is administered at time of 3rd injection. Embryos are recovered from donor cows 6-8 days after AI. Prostaglandin Fis administered immediately after embryo recovery

SERUM GONADOTROPHIN

(Equine chorionic gonadotrophin, eCG)

Indications. See Dose under preparation details

Warnings. Immune-mediated reduced effect after repeated doses, occasional anaphylactic reactions

Dose: See preparation details

Prescription-only medicine: Fostim 6000 (Pfizer) UK

Injection, powder for reconstitution, serum gonadotrophin 6000 units, for cattle, sheep, goats, pigs

Withdrawal Periods. Slaughter withdrawal period nil, milk withdrawal period nil

Dose: By subcutaneous or intramuscular injection.

Cattle: induction of oestrus in acyclic animals, anoestrus, 300-1500 units

Sheep: induction of oestrus outside normal breeding season, for synchronised mating, 300-800 units

Goats: induction of oestrus outside normal breeding season, for synchronised mating, 400-600 units

Pigs: anoestrus, 1000-1500 units

Prescription-only medicine: PMSG-Intervet (Intervet) UK

Injection, powder for reconstitution, serum gonadotrophin 5000 units, for cattle, sheep, pigs, dogs

Withdrawal Periods.

Cattle: (superovulation) slaughter 28 days, milk 48 hours after prostaglandin treatment at time of embryo collection; (other conditions) slaughter withdrawal period nil, milk withdrawal period nil. Sheep, pigs: slaughter withdrawal period nil, milk withdrawal period nil

Dose:

Cattle: oestrus control in acyclical maiden dairy heifers, by subcutaneous or intramuscular injection, 400-700 units, following treatment with pro-gestogen (Prid)

Superovulation, by subcutaneous or intramuscular injection, 1500-4000 units, see notes above

Sheep: induction of oestrus outside normal breeding season, by subcutaneous or intramuscular injection, 500 units at time of progestogen-impregnated sponge removal

Pigs: anoestrus, by subcutaneous or intramuscular injection, 1000 units

Dogs: oestrus induction (subnormal oestrus with non-acceptance), by subcutaneous injection, 20 units daily for 10 days, followed by intramuscular or intravenous injection, 500 units chorionic gonadotrophin on day 10