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Breeding and calves: Tackling haplotypes in the dairy herd

Since the introduction of genomic testing for Holstein cattle nearly 10 years ago, several genetic recessives, knows as haplotypes, have been discovered.

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Breeding and calves: Tackling haplotypes in the dairy herd

Haplotypes are a group of genetic recessives, usually effecting fertility, which were not recognised before routine genomic testing, as calf losses occurred before birth unlike more well-known recessives such as Brachyspina, BLAD or CVM.

 

Darren Todd, National Bovine Data Centre geneticist says: “Haplotypes are groups of alleles which are closely located on the chromosome and are usually inherited together. Not all haplotypes have negative effects, some have a neutral or even positive effect on production, conformation, health or fertility.

 

“Five haplotypes have recently been identified which are associated with embryo mortality and have a negative impact on the fertility of Holsteins. More often than not, when a haplotype is causing problems with failed conceptions or embryonic deaths, it does so silently, farmers are often unaware and may instead blame management, nutrition or the cow herself.”

Two haplotypes have also been identified in the Brown Swiss and Jersey breeds.

 

The five haplotypes identified do not have a negative impact when the animal carries only one copy of the gene. The problems arise when two carriers are mated.Table 1.0 Haplotypes and their frequency in each breed.

 

Of the resulting progeny, 25 per cent will be free from the haplotype, 50 per cent will be carriers of a single copy of the gene (heterozygous) and 25 percent will have two copies of the gene (homozygous).

 

This 25 per cent will die as embryos or be aborted, most likely the only sign of miscarriage will be the cow returning to heat at a later date.

 

The control and monitoring of haplotypes within the breed is extremely important, the consequences can be far reaching and have major effects. HCD is a haplotype which was traced back to a bull called Maughlin Storm.

Calves who are born homozygous for the HCD gene, where both parents were carriers, usually die within the first few months of life due to a cholesterol deficiency.

 

According to Mr Todd the easiest and cheapest way to minimise the impact of negative haplotypes on farm is to avoid using bulls which are carriers.

 

“If you are particularly conscious or have problems with fertility, it would be advisable to stay away from using these bulls.

 

50 per cent of AI bulls currently have their haplotype status published and this can be found following their name on the Holstein UK website.

 

For example HH1T would mean an animal is tested and free of the haplotype, and HH1C would mean they are a carrier.

 

However, avoiding carrier bulls is not always a feasible or practical solution, and another option is genomic testing.

As well as providing farmers with the conformation, health and production traits of each animal, haplotype status is an added bonus.

 

Owen Tunney, from Willows Farm vets says: “Genomic testing is a great way to allow you to use the full array of bulls available on the market without having to avoid carriers of genetic recessives. Identifying animals which are free from haplotypes avoids the risk of homozygous progeny and opens up the choice of genetics.”

 

Willows vets found that 25 per cent of 200 animals tested carried at least one genetic recessive, two percent carried more than one and eight per cent were HCD carriers.

 

“The information provided through genomic testing can also be used to create a mating programme to avoid mating carriers to carriers, and therefore rule out haplotypes as a cause of poor fertility. It is also a great way of maximising what you get out of genomic results,” says Mr Tunney.

 

Mr Todd adds: “Although the cost of genomically testing the whole herd may be restrictive, if you are planning on flushing a high genetic merit animal for embryos it would be extremely beneficial to genomically test beforehand to identify any haplotypes which may be present. “

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