“For dairy producers, controlling reproduction is one of the fastest ways to make an economic impact,” stated Stephen Foulke, DVM, DABVP, Boehringer Ingelheim. “And the key to successful breeding is making sure we achieve complete luteal regression as quickly as possible.”
Preparing Cattle for Breeding
The corpus luteum (CL) is a transient structure on the ovary that produces the hormone progesterone to maintain pregnancy. In an OvSynch program, prostaglandins (PGF2a) are used to accelerate the regression of the CL. After injection of PGF2a, blood levels of progesterone typically drop in about 30 hours. Once the CL regresses, the follicle produces estrogen, which brings about standing heat.
A Difference in Prostaglandins
“We used to think that the prostaglandins worked like turning off a light switch,” Dr. Foulke said. “But in reality, it appears that the uterus sends pulses to the corpus luteum, so it’s more like knocking at the door; it requires signaling over time to bring about luteal regression.”
Currently, there are two PGF2a products approved for luteolysis in lactating dairy cattle: cloprostenol sodium, which has a half-life of approximately 3 hours, and dinoprost tromethamine, with a half-life of about 8 minutes.1
“While dinoprost is quickly metabolized in the lungs and blown off, cloprostenol is metabolized in the kidneys, so it remains in the body longer,” explained Dr. Foulke. That means the latter may have more opportunities for signaling the CL.
In a study of lactating dairy cows, those treated with cloprostenol demonstrated a more rapid drop in serum progesterone in the first 12 hours after injection than those treated with dinoprost.2 This precipitous drop in progesterone appeared to increase the amount of estrogen produced by the follicle, potentially due to more pulses of luteinizing hormone, which encourages dominant follicle growth.
Putting Prostaglandins to the Test
A field study in a large dairy herd compared the use of cloprostenol and dinoprost in lactating cows.3 In the 78 percent of cows inseminated on days 3 and 4 after treatment, cloprostenol increased estrus detection rates in first-parity cows by 42.4 percent, compared to 34.0 percent in cows treated with dinoprost. First-parity cows treated with cloprostenol also experienced higher pregnancy rates of 38.3 percent versus 34.4 percent in dinoprost-treated cows.
Choosing the Right OvSynch Protocol
“The best synchronization protocol is the one you can get done on your farm consistently and accurately,” advised Dr. Foulke. He recommends working with your veterinarian to determine the fertility program that best fits your management style.
“As we increase our ability to control fertility, we can actually change the voluntary waiting period,” concluded Dr. Foulke. “While it has traditionally been 60 days, we can now push it out to 70 or 80 days, because we know we can get those cows bred.”