A new technique can help farmers artificially inseminate dairy cows at the proper stage in their reproductive cycle without continuous heat detection, say researchers at UW-Madison”s College of Agricultural and Life Sciences. The method can also reduce days open and reduce the number of cull cows, saving farmers about $50 per cow per calving interval.
The method, called Ovsynch, synchronizes ovulation and allows dairy farmers to inseminate unbred cows all at once, says CALS dairy scientist Milo Wiltbank.
Wiltbank and research associate Richard Pursley developed Ovsynch using two hormones already approved for dairy cattle: gonadotropin-releasing hormone (Cystorelin or Factrel) and prostaglandin (Lutalyse or Estrumate). Farmers interested in using Ovsynch just need to ask their veterinarians.
Ovsynch involves three injections. Gonadotropin-releasing hormone is injected in cows at any stage of their breeding cycle. This stimulates luteinizing hormone, which stimulates ovulation of old follicles and growth of a new follicle (follicles contain developing eggs). The second injection with prostaglandin, seven days later, kills the corpus luteum (an active corpus luteum would normally prevent the cow from ovulating). Two days later another injection of gonadotropin-releasing hormone releases the egg from the follicle (ovulation). This injection initiates ovulation in all cows at the same time. The optimal time for insemination is 16 hours after the third injection, but cows stay fertile for 24 hours.
“Essentially what you are doing is breeding to an ovulation instead of to heat,” said Wiltbank. It is important to understand that Ovsynch does not increase the pregnancy rate per artificial insemination, he said. Ninety percent of cows in the herd will have a synchronous ovulation after the Ovsynch treatment. However, the number of pregnancies from each artificial insemination is the same as when cows are bred after a detected heat, 40 percent per AI.
Farmers do not need to continuously watch for heat. Normal heat detection practices can be used to detect non-pregnant cows at 18 to 24 days after Ovsynch. Cows could also be resynchronized with Ovsynch if they are not found pregnant during a pregnancy check.
“The major disadvantage to Ovsynch is the cost of the hormones,” said Wiltbank. However, researchers found increases in profitability because cows were bred in a more timely manner. Ovsynch reduced the number of days open by about one estrous cycle (19 to 22 days). Fewer cows had to be culled because they did not become pregnant during lactation. In addition, cows that do not show heat or have cystic ovaries can be bred effectively after Ovsynch. Ovsynch is not effective in synchronizing heifers, Wiltbank notes.
In one study with 333 dairy cows, three Wisconsin dairy herds had a reduction in average days open from 118 days to 99 days after using Ovsynch. Herds that have more than 120 days open may experience a greater reduction.
“The university dairy has been using Ovsynch for three years and there are some farms that have been using this method for two years,” said Wiltbank. Ovsynch may be adopted as a breeding program for all dairy cows, or may be used only for problem cows.
The method is also an excellent research tool. “Ovsynch is helping us evaluate factors leading to low fertility in dairy cows that have high milk production,” Wiltbank said.
This research was published in two reports in the Journal of Dairy Science (Feb. 1997). Ovsynch is a practical application of basic research, conducted by Oliver Ginther at UW-Madison, using ultrasound techniques to study ovarian function in cattle. Wiltbank and Ginther are continuing basic research on the regulation of follicle development in dairy cows, under a joint grant from the USDA.