As it's prohibitively expensive to feed and care for a non-productive cow until the next time she has another chance to become pregnant, the operator often has to make the hard choice of selling her to the packing plant, Bilby said.
She's not just laid off; she's hamburger.
For decades, modern dairies rely mostly upon artificial insemination, using frozen sperm, to get cows pregnant as they come into heat. Since the late 1980s and early 1990s, embryo transfer systems -- test-tube calves -- have been used.
As the egg is fertilized in lab under climate-controlled conditions, the resulting in-vitro embryo is not subject to the heat-stress induced mortality rate of an in-vivo embryo, Bilby said. The in-vitro embryo is transferred to the mother cow when it is seven days old.
However, embryo transfers have issues of their own, he said. The first issue used to be cost of producing viable embryos by causing cows to super-ovulate -- producing large numbers of eggs at one time -- with fertility drugs. But today, there's an alternative. Eggs can be harvested from slaughterhouse cows, then fertilized in the lab with semen from high-quality bulls. Several hundred eggs can be fertilized at a time at a greatly reduced cost over super-ovulation methods.
Bilby's and Stewart's study used 722 cows from participating Central Texas dairies in the summer of 2009. The study compared fresh and frozen embryos that had been fertilized with sex-sorted semen, which is gender biased towards more female sperm, and incubated for seven days before transferred to the mother cow.
Bilby and Stewart split the cows into approximately three equal-size groups. One group was artificially inseminated with traditional methods. Another group received frozen embryos. The third group received fresh embryos.
All cows were estrus synchronized using standard methods. The artificial insemin
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Texas A&M AgriLife Communications