|SUPEROVULATION OF EMBRYO DONORS
Donor animals are super ovulated using a series of FSH hormone injections. Not all animals respond the same. In fact, variation to superovulation is one of the largest and most frustrating problems in embryo transfer programs in all species. The typical response is 6 to10 ovulations. But this response ranges from none to over 20. Owners must understand and accept the uncertainty associated with this part of the embryo program. Donors should not be overly fat, in good health and correctly vaccinated.
Embryos are usually collected from the donor 6-7 days after breeding. At Bosque Valley Reproduction Center, embryo collection is performed utilizing a non-surgical procedure. This technique minimizes surgical complications and allows for a more rapid recovery of the donor female.
The recovered flush fluid is examined under a microscope, and good embryos are separate from unfertilized eggs and degenerating embryos. A quality grade (1 being excellent and 4 being degenerated or unfertilized) and developmental stage is assigned to each of the recovered embryos. In most cases, excellent quality embryos result in the highest pregnancy rates. Lower grade embryos (grade 3) may be transferred fresh but not frozen and can result in a satisfactory pregnancy rate.
The graded embryos are transferred into the uterus of the recipient female whose estrous cycle has been synchronized with the donor. Usually two embryos are transferred into each recipient but singles are sometimes transferred. The quality of the recipient is probably one of the most crucial factors in the success of an embryo program. Bosque Valley Reproduction Center has been putting recipients together for clients for the past 13 years.
The purpose of freezing embryos is to hold the embryo in a state of suspended animation to be transferred at a later date. Grade 1 and 2 embryos can be frozen and stored in liquid nitrogen for an indefinite period of time. The frozen embryos can then be thawed and transferred with only a slight reduction in the pregnancy rate normally expected with fresh embryos. Reasons for freezing embryos can be: 1. Because not enough recipients are available at the time of embryo recovery. 2. Because the owner wants to target a specific kidding time. 3. Frozen embryos can be marketed.
WHAT FACTORS AFFECT THE RESULTS OF AN ET PROGRAM?
Results from ET programs vary greatly. Some programs are complete failures while others result in success beyond that expected. Most fall within the ranges and averages described. Failure of superovulation and failure of fertilization are the two reasons most programs fall below expectations. About 25% of donors fail to respond to superovulation. Some of those will again fail to respond when repeated. Others will respond normally. This high variability in results also occurs in cattle ET programs and is a priority for many research programs
FACTORS AFFECTING SUCCESS
Donor age: As with normal breeding, more ovulations are produced during the peak years of reproduction – typically 2 to 5 years. Younger or older donors generally produce slightly fewer embryos.
Season: Results are better during the breeding season in the months of August to late February. We are however currently having success flushing in the off season of March to July.
Stress: All goat farmers should know that stress reduces fertility. Stress will reduce the success of an ET program as well. The times most seriously affected by stress are at breeding of the donors, the care and preparing of the recipients, the time of estrus in the recipients, and the first two weeks following the ET in the recipients. Moving donors for breeding is not recommended. Moving donors for ET is not affected by stress - as the pregnancy is already established and the eggs are to be removed. Moving goat recipients may reduce pregnancy rates.
Body condition: Donors in particular should be in good body condition – ideally not to fat. Recipients must also be in good condition. Donors and recipients should be started on a plane of nutrition to allow a slight increase in body condition beginning two weeks prior to insertion of intra-vaginal devices. Salt and access to minerals should be provided.
Diet: Well-conditioned animals do not benefit from nutritional flushing. Poorly conditioned animals will benefit. Flushing should focus on energy not protein. Very high protein diets are associated with reduced embryo quality and increased early embryonic death in recipients. Diets high in legume might also contain phytoestrogens (plant estrogens) that are also associated with reduced fertilization and increased embryonic death. Selecting well-conditioned animals, in good health and on a sensible diet of good quality forage with a suitable grain supplement and adequate mineral is best.
Donor health: ET can be used to salvage genetics from donors affected by disease. Results suffer as body condition declines. Serious illness drastically reduces superovulation results.
Breeding program: Normally we recommend one buck to one or two superovulated donors.
Recipient quality: The quality of the recipient animals is one of the most crucial factors affecting success. Healthy recipients that have had at least one set of kids are best.
Heat detection: Detecting estrus in the donor and recipient animals and correctly recording this time is critical to the success of an ET program. Teaser animals play an important role in heat detection.