In cows, ovulation may be synchronized with a progestagen and estrogen combination treatment, a 2-dose PG regimen, or a GnRH and PG combination. Administration of PGF2α (25 mg, IM) or PG analog (cloprostenol at 500 μg, IM) to cows with a corpus luteum 7 days after ovulation results in estrus in ~2–5 days. Two PG injections given 14 days apart synchronize estrus and ovulation in most cows. Time to estrus is more variable than with progesterone suppression, so insemination should be based on detection of estrus. Ovulation may also be synchronized by administration of GnRH, 100 μg, IM (day 1), followed by PG treatment on day 7–8 and a second GnRH treatment on day 10. Cows should be inseminated 0–20 hr after the second GnRH treatment. This GnRH and PGF2α protocol is termed “ovsynch.” There are many variations on this protocol, using additional steroids, PG, or GnRH treatments, that may increase the degree of synchrony or pregnancy rates after artificial insemination.
A controlled intravaginal drug-release (CIDR) device may also be used. This device contains progesterone and is labeled for estrus synchronization in beef and dairy cattle. Cows are administered GnRH, and the CIDR is inserted for 7 days and then removed, with cows receiving a concurrent injection of PGF2α. Cows are inseminated, with or without another GnRH injection, 48–72 hr after PGF2α injection. The most effective synchronization treatment, an IM injection of a combination of 5 mg estradiol valerate and 3 mg norgestomet, with an ear implant of 6 mg norgestomet left in for 9 days, is no longer commercially available in the USA because of the ban on the use of estrogens in food animals. Note that all estrus synchronization protocols are less effective in Bos indicus cattle and their crosses than in Bos taurus cattle.
Ovulation may be induced in cows with mature follicles (10–15 mm diameter) by treatment with GnRH at 100–250 μg, IM; luteinizing hormone (LH) at 25 mg, IM, or hCG at 5,000–10,000 IU, IM. Because the endogenous LH peak develops at the onset of estrus, this administration will not speed the time of ovulation in estrous cows but may be used to ensure luteinization in cows with histories of cystic ovarian disease or to induce ovulation in anestrous postpartum cows.
Superovulation may be achieved in cows by treatment with eCG (not currently commercially available) in mid-diestrus followed by PG-induced luteolysis 2–3 days later, or by treatment with FSH (potencies differ, refer to label instructions), typically IM, bid for 4–5 days, with administration of PG (25–35 mg, IM) usually on day 3 or 4 of treatment. FSH treatment is discontinued at the onset of estrus.
Last full review/revision July 2011 by Steven P. Brinsko, DVM, MS, PhD, DACT