Insemination-Related Factors Affecting Fertilization in Estrous-Synchronized Cattle
by Barb Baylor Anderson for Angus Productions Inc.
NASHVILLE, TENN. (Aug. 5, 2010) — Beef producers may have the tendency to focus on the female side of reproduction, but Richard Saacke, professor emeritus with the Virginia Tech's Department of Dairy Science, said the male side of the equation may be just as complex. He outlined four major factors that producers should consider when it comes to fertilization in estrous-synchronized cattle during the Applied Reproductive Strategies in Beef Cattle (ARSBC) Conference in Nashville, Tenn.
Virginia Tech’s Richard Saacke outlined four major factors that producers should consider when it comes to fertilization in estrous-synchronized cattle.
Those factors include sperm transport in the cow, reproductive history and source of preserved semen of the bull; placement and semen handling by the inseminator; and insemination timing.
“In most breeding strategies, whether estrous synchronization is employed or not, the semen quality, placement and timing of insemination are critical to successful pregnancy,” he said.
For beef cattle, Saacke said six to 16 hours are needed for sperm to travel and colonize in the female egg reservoir. Various studies of embryos and other research seem to confirm that the motile and better-shaped sperm appear to be the most viable. While millions of sperm may be placed by an inseminator, only thousands reach the reservoir, which Saacke says is how nature intended. The female’s system affects what sperm may reach the egg.
“We now know success or failure of an AI dose due to the male or inseminate resides in whether or not the egg was fertilized or whether or not the embryo developed normally and hatched in time to signal pregnancy to the dam. Both scenarios are embraced by semen quality and quantity, and they must be considered together to address pregnancy rate,” he said. “Fertility increases with increasing numbers of viable sperm delivered to the cow up to a threshold, after which limiting factors in the female population become important and further increases in sperm are without effect on fertility. The minimum number of motile sperm required for maximum fertility differs among bulls. Bulls also differ in the maximum fertility at any dosage.”
Saacke said clearly while producers should pay attention to semen dosage, the bull selected, natural service or the timing of artificial insemination (AI), most emphasis should be placed on the male selection and AI timing together.
“Some bulls can be compensated for with more sperm added. Others cannot, and those are the bulls that need to be removed from the beef cattle population,” he said.
In problem bulls, abnormal sperm may be just the tip of the iceberg, added Saacke. Fat deposition in bulls can affect testicular temperature, and elevated testicular temperature results in the production of abnormal sperm and vulnerability of sperm DNA to acid denaturation. The result can be abnormal shaped sperm and normal shaped sperm in abnormal samples.
Saacke said major AI stations and veterinarians usually understand the sperm morphology, and can make adjustments in the AI process to help compensate. AI technicians may need greater training to do a more consistent job in increasing the success rate.
“The shift from ampule to straw has given technicians better thermal control of semen,” he said. “And while technicians may know where the sperm goes, they need proper training to be sure of accurate placement. Bottom line, inseminators can act like bulls — one may require more sperm than another during the process to get it right.”
Additionally, Saccke said, AI timing generally needs to be closer to ovulation while more sperm needs to get to the egg. He explained that the fertilization rate may go up with accessory sperm, but the number of excellent to good embryos goes down.
“AI is a compromise, and if you breed late, you increase the fertility rate and decrease the embryo quality,” he said. “Producers should ovulate early and breed earlier to allow the 6-10 hours it takes for the sperm to get there. Use a high-fertility bull, and you can inseminate over a period of time and still get good results and work with better sperm.”
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