BH2 - A Haplotype impacting Stillbirth

A haplotype is a combination of alleles (DNA sequences) at adjacent locations on a chromosome that are inherited together. When a calf inherits a haplotype from both the sire and dam as a homozygous recessive, it may be stillborn or die soon after birth. In Europe, two calves that died shortly after birth have been discovered as homozygous for BH2. A list of BH2 carrier bulls is now available to breeders. The list is also published in this (November) issue of the Brown Swiss Bulletin and breeders are encouraged to utilize it when making mating decisions as to avoid mating two carrier animals. The BH2 Carrier list will be updated with each sire evaluation run.

Further research is being gathered in the U.S. and tests are in process to determine if stillborn calves that have been found as having carrier parents are homozygous for BH2. The ultimate goal is to identify this gene by working with USDA and worldwide research centers as to not duplicate research. Making efforts to avoid inbreeding when selecting matings will also assist in avoiding stillbirth, SMA, SDM, BH1, BH2 and other potential genetic defects that have not yet been discovered.

From New Fertility and stillbirth haplotypes and changes in haplotype status

By Paul Van Raden, Dan Null, Jana Hutchison and Tabatha Cooper (USDA-AIPL):

“The BH2 carrier frequency gradually increased from 4% before 1980 to 20% today. Nearly all carriers trace to U.S. Brown Swiss bull 144488 Rancho Rustic My Design born in 1963. Schwarzenbacher et al. (2012 EAAP meeting) discovered BH2 (which they labeled 19-1) on chromosome 19 at a range of 10.6-11.7 Mbase. The effect of BH2 is significant in both U.S. and Austrian data for stillbirth (not fertility), and the rate of calf loss is similar to the previously known defect SMA. No homozygotes for BH2 were found in U.S., Austrian, or Intergenomic Brown Swiss genotypes even though 29 were expected. Swiss and Austrian researchers recently identified 2 BH2 homozygous calves born with low birth weight that died from poor immune response, and are now using sequence data to locate the mutation causing the calf loss.”

Genetics

CDCB Genetic Evaluations

BH2 - Haplotype Affecting Stillbirth

BH1 - Haplotype Discontinued

BH2 CARRIER LIST (08-18)

Take‐home points

1) The term “haplotype” refers to a group of SNP markers that are located at adjacent positions on the chromosome and are usually inherited together.

2) Modern genomics tools have been used to identify thousands of haplotypes on each chromosome, and each has a positive, neutral, or negative association with production, conformation, health, and fertility.

3) Scientists have identified five haplotypes that haven’t been found in a homozygous state in genotyped animals and have a negative effect on conception rate when present in the sire and maternal grandsire.

4) The exact genes and their underlying biological roles in fertilization and embryo development are unknown, but it is assumed that the outcome of inheriting the same haplotype from both parents is failed conception or early embryonic loss.

5) The reactive approach of attempting to eradicate every animal with an undesirable haplotype is not recommended in light of their economic impact, and is not practical given the likelihood that many more undesirable haplotypes will be found.

6) The impact of these haplotypes is already reflected in published evaluations for sire conception rate and daughter pregnancy rate, as well as the Lifetime Net Merit index.

7) Producers should neither avoid using bulls with these haplotypes nor cull cows, heifers, and calves that are carriers, because this will lead to significant economic losses in other important traits.

8) Computerized mating programs offer a simple, inexpensive solution for avoiding affected matings, so producers should use these programs and follow through on the mating recommendations.