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Embryo Transfer (ET): Data Collection And Utilization
Due to selection placed on parents and the additional financial investment with the ET process, potential seedstock animals resulting from ET need to have proper, uniquely designed, genetic evaluation in order to have a role in genetic progress. Therefore, maximizing the accuracy of genetic predictions early in the animals’ lives by using the animals’ own observations along with those of relatives has increased importance. But, for maternally influenced traits such as weaning weight, the genetic evaluation model must be modified slightly to account separately for the donors’ contributions to the genetics of the calves and the recipient cows’ contribution to maternal environment. Because of the increased investment, breeders may be motivated to provide preferential treatment that must be accounted for through appropriate contemporary grouping.
Recipient dam considerations
Effects on the phenotype due to the dam of the animal are present in traits measured up to weaning, but generally assumed not present in phenotypes measured post-weaning. These include both genetic and non-genetic effects. For animals produced using ET, these maternal influences are due to the recipient dam, and not the embryo donor dam. Therefore, information on the recipient dam for these maternally influenced traits is necessary to reliably include the observations in genetic evaluation. Both age of the recipient dam and its breed composition will affect maternally influenced traits - i.e. birth weight, calving ease, and weaning weight.
Ideally, pedigree information on the recipient would be included but it is not always available, as recipients are often commercial females. Some organizations producing genetic evaluations will not use observations resulting from non-registered recipient females. Other organizations will use these observations when age and breed composition of the recipient are known.
Modeling Records of ET Animals in Genetic Evaluation
Recipients in genetic evaluation
Methods for modelling the effects of recipient dams are in the literature[1][2][3][4] and can be easily incorporated in genetic evaluations if sufficient information about the recipient dams is available. Specifically, both the maternal additive genetic effect and the permanent maternal environment effect should be associated with the recipient dam instead of the donor dam.
Suitability of Multiple Ovulation Embryo Transfer (MOET) records for genetic evaluation
Calves produced by MOET had greater birth weight than non-ET calves, although the data structure was far from ideal for estimating such effect.[5] Nonetheless, the data structure was well-suited for estimation of heritability in subsets of the data. Heritability of birth weight of non-ET calves, and ET calves with Holstein, beef crossbred, or unknown breed recipients was 41.4±4.3, 28.4±3.1, 32.4±3.8, and 32.5±3.4%, respectively.[5] The heritabilities of ET calves included residual variance resulting from transfers of mixtures of fresh and frozen, sexed and un-sexed embryos and probably countless other variations in ET processes, none of which were available for the analysis. Consequently, the heritabilities of ET records are expected to be higher if the information recommended below for collection had been available. Thus, birth weight records from calves produced by MOET are suitable for use in genetic evaluation even with little or no information on the recipient breed and age (excluding heifers) or the variations on MOET techniques performed. In such cases, it would be preferable to fit additional residual and/or permanent environment variance to the model for such records. Nonetheless, it is far preferable to have as much information as possible on the recipient cows, and where feasible, to use registered recipients that have several previous recorded calves. Furthermore, it would be useful to record whether MOET calves were produced from fresh or frozen transfers, were biopsied for sex determination and/or genotyping, and whether any other substantial variations in ET technique were performed.
Recommendations
BIF recommends that observations from animals resulting from MOET, for traits that do not have maternal effects, be used in genetic evaluations provided any preferential treatment, if given, is accounted for by assigning an appropriate contemporary group code.
BIF recommends that observations from animals resulting from MOET, for traits that have maternal effects, be used in genetic evaluations as long as the recipient dams' ages (heifer, 1st parity, or multiparity) and approximate breed compositions are available, and any preferential treatment, if given, is accounted for by contemporary grouping.
BIF recommends use of recipient cows with known pedigrees well-tied to the genetic evaluation as being preferable to recipients with unknown pedigree and no previous calves with records in the genetic evaluation. Where this is not practical, each recipient dam should be assigned a unique identifier so occurrences of multiple ET calves with the same recipient are properly accounted for.
BIF recommends that embryo stage (1-9)[6] and grade (1-3)[6] and whether frozen, split, sexed, or genotyped be recorded and submitted to breed association or other recording organization. BIF recommends that, when sufficient information becomes available, genetic evaluation models for MOET calves include effects of fresh versus frozen and of biopsied (sexed and/or genotyped) or not.
BIF recommends that records of animals produced by MOET should have separate contemporary group effects in the genetic evaluation from records of animals produced by AI or natural service. However, animals produced by MOET should be included in the same management code (as determined by the breeder) as animals not produced by MOET (including AI or natural service calves) that were managed identically in the same group so their common environmental effect can be accounted for in future genetic evaluations. Major differences in age, breed, origin, etc. among recipients should also be accounted for in genetic evaluation models.
BIF recommends to not use phenotypic observations in genetic evaluation from animals resulting from In Vitro Fertilization (IVF), Nuclear Transfer, or that are not explicitly known to have resulted from natural service, AI, or MOET in genetic evaluations. BIF recommends that observations on ET calves be recorded and submitted to breed association or other recording organization, along with the form of technology (as listed above or others not listed) used to produce the ET calves.
BIF recommends that for genetic evaluations of traits with maternal effects, that direct effects (breeding value, genomic effects, breed composition, heterosis, etc.) be assigned to the donor or natural dam, and maternal effects (breeding value, genomic effects, breed composition, heterosis, permanent environment, etc.) with the recipient dam.
BIF recommends that records for reproductive traits collected subsequent to superovulation not be used in genetic evaluation.
Citations
- ↑ Schaeffer, L. and Kennedy, B. 1989. Effects of embryo transfer in beef cattle on genetic evaluation methodology. Journal of Animal Science 67:2536-2543.
- ↑ Van Vleck, L. D. 1990. Alternative animal models with maternal effects and foster dams. Journal of Animal Science 68:4026-4038.
- ↑ Suárez MJ, Munilla S, Cantet RJ. 2015. Accounting for unknown foster dams in the genetic evaluation of embryo transfer progeny. J Anim Breed Genet. 2015;132(1):21‐29. doi:10.1111/jbg.12121.
- ↑ Thallman, R. M. 1988. Prediction of genetic values for weaning weight from field data on calves produced by embryo transfer, M.S. Thesis, Texas A&M University, College Station.
- ↑ 5.0 5.1 Thallman, R. M., J. A. Dillon, J. O. Sanders, A. D. Herring, S. D. Kachman, and D. G. Riley. 2014. Large Effects on Birth Weight Follow Inheritance Pattern Consistent with Gametic Imprinting and X Chromosome. In: 10th World Congress on Genetics Applied to Livestock Production, Vancouver, BC Canada
- ↑ 6.0 6.1 Stringfellow, D.A. and M.D. Givens. 2010. Manual of international embryo transfer society (IETS). 4th ed. Champaign, Illinois: International Embryo Transfer Society.
