The screening method used previously in human fertility services will help producers make the best breeding decisions
When couples have difficulty conceiving a child, they may consider the services of a fertility clinic for in vitro fertilization.
The process leading to an embryo being implanted in the uterus involves many biological tests and, for some, it will also involve genetic screening, especially when one of the parents might be carrying a challenging inherited condition.
The screening is called karyomapping and the procedure will identify the presence of a defective gene or a chromosomal abnormality that might be passed on. Then, before implantation, karyomapping screening is conducted on the embryo to confirm it is not carrying the defective gene.
Now, the karyomapping screening application is available to cattle embryos.
The procedure will allow breeders to make the best decisions for top quality genetic stock at the embryo stage rather than waiting until a calf is born. The process will allow for breeding herds to build genetically healthy offspring much faster, more efficiently, and more economically.
“Karyomapping is a screening for the whole genome of an embryo,” said Darren Griffin, professor of genetics in the School of Biosciences at the University of Kent in the United Kingdom.
“In humans, it tells us whether an IVF embryo is carrying a single gene and/or chromosome disorder simultaneously. In cattle, it tells us about certain breeding traits and chromosome disorders. The hope is that it will ultimately help improve IVF success rates in cattle.”
Griffin said that the computer algorithm had to be adapted to take into account that the genome structure of cattle is different to that of humans. Even though the biological systems are similar, cattle embryos are somewhat fattier than human IVF embryos.
A huge advantage of a whole genome screening of cattle embryos is that it can influence or even increase the generational health of a herd. Griffin said that, by introducing health-related traits such as disease resistance, the interventions are permanent, sustainable and can lead to a reduction in the use of antibiotics.
“By screening embryos, we can potentially introduce new genetic lines more quickly and efficiently,” he said. ‘In the future, it may also help cut down on animal transportation, which could have biosecurity and environmental benefits.”
The ease of moving genetically screened embryos from one geographical region to a breeding farm in another area rather than shipping live animals would clearly be more efficient, economical and environmentally friendly.
However, in IVF cattle embryos, aneuploidy is common. Aneuploidy is the condition in which there is an abnormal number of chromosomes and is a leading cause of developmental arrest. In humans, an extra or missing chromosome is a common cause of genetic disorders and birth defects. Karyomapping used on cattle embryos can not only source genomic abnormalities but also detect aneuploidy and characterize the frequency and parental origin of the condition, thus providing more selective breeding options in the future. Knowing parental carriers of genetic anomalies allows breeders to permanently remove them from the breeding stock.
Research and trials were funded from a government grant while PhD students working on the project are industry-funded. The exciting potential for this genetic screening is that it will have a worldwide application, including future opportunities for Canadian breeders.
“The embryos are generated in the lab and the screening is out-sourced,” said Griffin. “We would like to see (the system) used as widely as possible. Cattle embryology is commonplace across the world. In order to get DNA from the embryo, we currently take a few cells from it. This is standard and safe (but) it is quite labourious. We are working on ways of looking at DNA shed into the medium by the embryos. Interpreting the screening results is something we could do remotely, getting data electronically from any screening lab in the world.”
While IVF embryos are used widely in cattle breeding, Griffin said that their study is the first in which the embryos have undergone a whole genomic screening before implantation. Using the karyomapping system to detect for genetic abnormalities means there are significantly fewer chances of embryos with compromised health defects developing into live-born calves.
The study on karyomapping cattle embryos resulted in the first successful use of the technique this fall. On a farm near Penrith, in northern England, the first healthy karyomapped calf was born and named Crossfell Cinder Candy.
At the human level, screening embryos for genetic abnormalities is common in the U.K. with some exceptions.
“Among some, it can be controversial,” said Griffin. “Most but not all of the IVF community think it is a good idea. In cattle, our study was the first ‘proof in principle.’ ”
The research was published in the journal Theriogenology and the team at the University of Kent worked in collaboration with the University of Nottingham and the Paragon Veterinary Group in Cumbria.