Breakthroughs in biotechnology continue to equip beef producers with the tools they need to improve the quality and productivity of their cattle. In fact, the list of biotechnologies available today is expansive, ranging from artificial insemination to embryo transfer, to cloning and in vitro fertilization.
Yet success or failure in their application depends greatly on individual operating situations. "All of these biotechnologies can be applied profitably in some circumstances, but none of them will be universally profitable," says Dr. George Siedel, an animal reproduction scientist from Colorado State University. Seidel believes that knowledge of their various benefits and drawbacks - and planning before you use them - are the keys to making them work most effectively.
A discussion of various biotechnologies - including their benefits and drawbacks - continues below.
One of the best-known biotechnologies is embryo recovery and transfer (ET), remarks Seidel. Currently, ET is the third most commonly used biotechnology, after AI and estrus synchronization. As new techniques such as inexpensive, reliable sexing or cloning become available, ET will be used more frequently, he says.
In ET, a donor cow of superior breeding is chemically induced to produce an unusually large number of eggs (a process called superovulation). The eggs are then fertilized within the donor cow, allowed to develop and removed and implanted in a recipient cow. Between removal and implantation, the eggs may be frozen for safekeeping, a process known as cryopreservation.
"The currently stable, mature ET industry produces 40,000 to 50,000 beef calves every year in the U.S. and Canada," says Seidel. "This represents only about 1 in every 700 beef calves born, but, since ET animals are used extensively for breeding, they end up in the pedigrees of many bulls used for natural breeding and AI."
Like any other biotechnology, ET has advantages and disadvantages. In most cases, an ET calf costs between $500 to $1000 more to produce than a calf born of conventional reproduction, Seidel says. Therefore, nearly all ET use currently is within registered cowherds. The highest costs occur when poorly trained personnel work with low-quality cattle, resulting in low pregnancy rates. "The major cost of embryo transfer is not in the technology itself, but rather in costs that occur due to delaying pregnancy in normal, healthy recipients,"Seidel says. "Whether recipients are kept from pregnancy while embryos are recovered from donors, or frozen embryos are used (which may cause pregnancy rates to dip 10% to 15%), some delay in getting the recipient pregnant usually occurs."
Although trained technicians usually do the job, ranchers can learn to do ET themselves, Seidel remarks. "The single-most important thing one can do to improve or maximize embryo transfer success is good recipient management," he says."This includes nutrition, appropriate postpartum management, proper vaccinations and so on."
Fees for embryo transfer training can be as high as $3,000 to $4,000. Considerable experience with artificial insemination is required for embryo transfer training. However, the major cost of training comes after schooling- most people show low rates of success for their first 10 to 25 donors and 50 to 100 recipients.
Successful ET programs require at least 12 to 15 recipients, and pregnancy rates without using cryopreservation can exceed 70%, Seidel says. "However, under most conditions, pregnancy rates are in the 60% range with good management and unfrozen embryos," he says. "With frozen embryos, pregnancy rates fall about 10 %. Of course, excellent heat detection is required for any degree of success."
Scientists have used in vitro fertilization to solve infertility problems in humans for many years. Animal scientists use this biotechnology in cows with blocked oviducts or in cows that do not respond well to superovulation. The procedure can even be used to obtain pregnancies from a cow that is slated for slaughter, or one that has already been slaughtered. In 1995, about 4,000 calves will be born in the U.S. and Canada through in vitro fertilization.
In this procedure, a technician removes unfertilized eggs (called oocytes) from the donor cow's ovaries via a needle through the vaginal wall. This can be done with or without superovulation drugs at any time during the cow's reproductive cycle, even during the first 100 days of pregnancy, and as often as every three to four days. Technicians usually recover six to eight oocytes per session, and must discard about 40% of these due to abnormalities.
After the oocytes mature inside an incubator (a 20- to 24-hour period), they are introduced to sperm that have also been incubated for a short time (one to three hours), remarks Seidel. The resulting fertilized eggs, called zygotes, are then allowed to incubate overnight. Usually, 75% of the three to five normal oocytes from each procedure are successfully fertilized. They are then allowed to develop in the laboratory for nearly one week and subsequently placed into the recipient. Pregnancy rates from in vitro fertilization are usually in the 40% to 50% range.
Although in vitro fertilization can produce many fertilized embryos at a relatively low cost, Seidel cautions, the added expense of the required embryo transfer makes the procedure cost prohibitive in most cases. Additionally, the procedure is complicated and requires a laboratory.
Although many different techniques to determine the sex of embryos are currently under development, only one sexing method is currently available commercially. In this procedure, technicians remove a few cells from the embryo and probe the DNA in these cells for the presence of a Y-chromosome. The Y-chromosome determines that the embryo is male.
This process successfully determines sex more than 90% of the time - provided the technicians are skilled, explains Seidel. The time and skill required to biopsy embryos is a major drawback to the process, as is the fact that sexing cryopreserved embryos has a higher rate of failure. However, since sexing embryos permits extremely efficient use of recipients, sexing can provide considerable genetic and economic benefits when costs of embryo transfer can be justified for one sex of calf but not the other sex.
"Development of a quick, non-invasive procedure that is accurate and inexpensive is crucial to the long-term prospects of sexing," says Seidel. A cost of $15 to $20 per head would probably be extremely attractive to herds already using ET extensively. In fact, low cost, accurate sexing technology would greatly expand and enhance embryo transfer, he adds.
Seidel adds that if a procedure for reliable sexing of sperm were ever developed, sexing of embryos would become obsolete. Already scientists can sort sperm with 90% accuracy by a process called flow cytometry, a method more commonly used with in vitro fertilization because the process is too slow to provide enough sperm for artificial insemination.
More than a decade ago, researchers began bisecting - or splitting - embryos to provide twins for research. They proved the procedure can be done with rather simple equipment by a technician with minimal training. "But embryo splitting is time-consuming," remarks Seidel. "In fact, the main cost in the process is labor, which can run more than $50 per embryo split. Many embryo transfer companies do splitting free of charge, because there are then twice as many embryos to implant."
About 50% more calves are obtained when embryos are bisected and then implanted, says Seidel. Pregnancy rates per half embryos are only about 10 to 15 percentage points lower than whole embryos.
At the same time, only about 1% to 2% of calves from embryo transfer in North America result from bisected embryos. So why isn't this simple procedure used more widely? The tools are costly, and the process takes time and patience, Seidel responds.
Often people involved in recovering, isolating, transferring and freezing embryos don't have time to add splitting to the list," Seidel says. "In addition, splitting does not work well when combined with freezing. Combining the two techniques results in considerably lower pregnancy rates. And, in most cases, producers don't want large numbers of calves from an individual donor. This is due in part to lack of market for excess bulls, a problem which could be solved by sexing."
Cloning by nuclear transplantation is an extremely expensive process, says Seidel. So expensive, in fact, that only 1000 calves have been produced by this procedure - almost all of them by private companies.
The process involves taking an in vitro matured oocyte, or unfertilized egg, and microsurgically removing all its chromosomes, explains Seidel. The individual cells of separate embryos are then fused to the oocytes by electrical pulses. The process results in 20 to 30 genetically identical, one-cell embryos that are then cultured in vitro for one week and transferred to recipients.
"Published reports indicate that most attempts to clone by this method are complete failures, with no calves produced,"remarks Seidel. "On the other hand, a few attempts have produced six or more calves per try."
The main shortcoming of the procedure remains the huge resources in personnel, equipment and animals needed for producing large numbers of cloned, full-term pregnancies. Oftentimes, the procedure results in abnormal calves with high mortality rates . "Many of the calves are larger than normal, some up to 50% larger than breed averages," he remarks. "Additionally, many of the calves had metabolic abnormalities like hypoglycemia and hypothermia.
"A very long-term plan will be needed along with huge financial resources and an infrastructure to apply this technology," Seidel concludes. "It is likely that it will be 12 to 15 years before cloning by nuclear transplantation will be used on a large scale in cattle."
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