Management Factors Influence Fertility
in Synchronized and Natural Programs
by Barb Baylor Anderson for Angus Productions Inc.
NASHVILLE, TENN. (Aug. 6, 2010) — The cost of reproductive failure in the U.S. beef and dairy industry tops $1 billion annually. But George Perry, South Dakota State University animal scientist, said by maximizing the equation of reproduction, producers can achieve greater pregnancy rates. Perry spoke at the Applied Reproductive Strategies in Beef Cattle (ARSBC) Conference in Nashville, Tenn.
By maximizing the equation of reproduction, producers can achieve greater pregnancy rates, said SDSU's George Perry, sharing practical ways to do just that.
"The majority of loss occurs because cows do not become pregnant during a defined breeding season. Therefore, the goal of any breeding program, artificial insemination (AI) or natural service, synchronized or not, is to maximize the number of females that become pregnant," he said. "That means fertility plays a major role in the success of any breeding program."
Perry explained that beef cow fertility can be influenced by many factors. He recommended looking at four major factors through an “equation of reproduction." The equation includes percentage of animals detected in standing estrus and inseminated, percentage of inseminator efficiency, percentage of fertility level of the herd, and percentage of fertility level of the semen.
"In a perfect world, these should total a 100% pregnancy rate," he said. "But what if each factor is only 70%? The pregnancy rate would only be 24% for single service."
Perry broke down the equation, looking first at animals detected in standing estrus — a necessity for successful insemination. But AI conception rates may be lower, even if producers are detecting heat. Natural service is a similar problem. You need to watch the libido in bulls.
"This is why fixed-time AI has become important and we have aids to help with that," he said. "Some animals may not show estrus while others may not ovulate."
Since the timing of estrus can be spread throughout the day, Perry said synchronizing can shift distribution of estrus timing. Fixed-time AI eliminates the need for estrus detection and sets up for better conception. In this instance, producers may achieve 90% success.
"Inseminator efficiency is the second factor. You have to be in the right place at the right time," he said, adding that mistakes can occur. "Sexed semen must be handled even more carefully. With natural service, some bulls are not physically able to service the herd."
In both instances, though, Perry said he sees no difference in pregnancy rates. He estimated for his example a 95% success rate with inseminator efficiency.
The third area is the fertility level of the herd, which Perry says is the most complicated.
"The fertility level of the herd is affected by cycle status, compliance with protocols, body condition scores, disease control, embryonic mortality and stress," he said.
For example, in the case of embryonic mortality, management decisions can affect the incidence of its occurrence. Shipping stress in heifers, especially, heat stress and nutrition restriction can also affect embryonic mortality rates. Perry assigns a 90% success rate to the factor.
The final factor is fertility level of the semen. "If you do the best you can, you may get about 95% success in this area," Perry said. "Combining the four factors into our equation, 90%, 95%, 90% and 95%, you end up with a 73% pregnancy rate for single service.
"It is clear reproduction is complicated," he continued. "Everything must be lined up. Recordkeeping becomes even more important. You have to be a perfectionist."
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