GENOMICS for BREED IMPROVEMENT la GÉNOMIQUE pour L’AMÉLIORATION de la RACE

Kathryn Roxburgh examines using genetic testing as a herd management tool.

Kathryn Roxburgh examine les tests génétiques comme outil de gestions du troupeau.

The Jersey breed represents a very competitive 4% of the Canadian dairy market today, and is gaining popularity because Jerseys can efficiently produce high-component milk.

In order to maintain our competitive edge and grow the number of Jerseys in Canada, Canadian Jerseys must be bred to be even more efficient, and produce even more milk solids. North America has the Jersey genetics needed to push the Jersey breed forward. We just have to find those outliers and get the most out of them! At the same time, we need to identify those animals who are carriers of undesirable genetic anomalies and manage those animals accordingly.

Genomic testing can be used as an effective and practical management tool. It can do so much more for your herd than simply help you find that super-high GLPI cow for you to market. Genomic testing is used to predict economically important traits, such as milk production, milk composition, female fertility, productive life, calving ability, disease resistance, and functional conformation. Genomic testing is also used to identify carriers of the JH1 and JH2 haplotypes.

When used effectively, genomic testing will save you money.

Genomic testing, when coupled with registration, milk recording, and classification, is the best way for the Jersey breed to make genetic progress. By testing as many females as possible, we can increase the probability of finding the outlier genetics that have been transmitted in the Jersey population. As more and more Jerseys are tested, breeders are more likely to find the females whose genetics will improve our breed the most. Once we know which animals will bring the most genetic gain to the Jersey breed, we can put more energy into developing those bloodlines.

At the same time, once we know which animals will bring the least genetic gain to the Jersey breed, those animals can be removed from the herd, no longer costing money to feed and house.

Another helpful way genomic testing contributes to the genetic gain of the Jersey breed is by identifying which animals are carriers of one of the two Jersey haplotypes, known as JH1 and JH2. The only way to know for sure if an animal is a carrier is from a genomic test. By reducing the number of times where a JH1 carrier female is mated to a JH1 carrier male, we reduce the probability of embryo death, and increase the chances of a pregnancy at first breeding. Less time and money are spent on repeat breedings, and there will be fewer days open. As each individual Jersey herd strives for greater genetic progress, the better our breed as a whole will become. The overall progress of our breed is the collective result of individual management decisions made on farm.

GENOMICS NEEDS CLASSIFICATION AND MILK RECORDING

Genomic testing uses genetic information for a given animal and compares her genome to a reference population with known phenotypes. A phenotype is the physical expression of a gene, such as actual milk production, milk components, and physical conformation. A genomic evaluation is a way of saying, “Other Jersey cows with the same genomic markers as this heifer went on to produce ‘x’ kg of milk, at ‘y’ percent fat, and ‘z’ percent protein, and had a productive life of ‘xx’ years. It is safe to say that this heifer will, too.” Genomic evaluations of the future depend on proper animal identification, official milk records, and classification today. We need the actual, real life performance data to match with the genetic information. A genomic profile is only useful if it can be compared to actual phenotypes in the population. Genomic testing doesn’t replace milk recording and classification. We still need herds to milk record and classify, otherwise the genomic test numbers don’t mean anything.

GENOMICS FINDS JH1 AND JH2 HAPLOTYPE CARRIERS

A haplotype is a chunk of DNA from a single chromosome, usually inherited as a group. One copy of the haplotype is inherited from each parent, and if an animal has two identical copies of the haplotype, the animal is said to be homozygous for that haplotype. When an animal carries two copies of a haplotype, it will not survive past the embryonic stage.

In the case of the JH1 and JH2 haplotypes, we will only ever find heterozygous carriers: that is, animals with a single copy of the specific JH1 or JH2 haplotype. This is because homozygous carriers will not live past being an embryo. The embryo will die, and the dam carrying the embryo will come into heat once again.

When a JH1 carrier is mated to another JH1 carrier, there is a 1 in 4 chance that the resulting embryo will not survive. The JH1 carrier female will be thought simply to have not caught to the breeding. The same applies for carriers of the JH2 haplotype. By reducing the number of times where a JH1 carrier female is mated to a JH1 carrier male, we reduce the probability of embryo death, and increase the chances of a pregnancy at first breeding. Less time and money are spent on repeat breedings, and there will be fewer days open. Given that these haplotypes can be found in almost one out of every four Jerseys in North America, it is important to know who is a carrier, and who is not.

It is not recommended to avoid using carrier sires altogether. A sire being marketed by an AI company despite being a JH1 or JH2 carrier likely has a lot of other positive traits to offer, which likely outweighs the fact that he may pass on a recessive gene. These sires simply need to be used appropriately on females known to be non-carriers.