Genetic causes for abnormalities in Holstein calves identified

The constantly increasing number of genotypings in the Holstein population serves for a better selection possibility as well as for a faster increase in genetic progress. Additionally, it has the advantage that when undesirable traits occur (e.g. weak or non-viable calves), investigations can be started promptly to diagnose the genetic cause. In the past months, genetically determined traits could be discovered in calves with limited viability. Investigations for genetic carriers will begin soon and help to improve the survivability of calves in the future by avoiding risk matings.

CALF RECUMBENCY

“Recumbency” means the unintentional “lying down” of cattle. In calves this symptom was observed by two US farmers. They reported that their viable calves were not able to stand up on their own. Responsible for the recumbency of affected calves is an existing muscle weakness, so this abnormaly is also called "Early onset muscle weakness". This prevents the calves from standing up and remain standing on their own. After 18 affected animals and the same number of control animals were genotyped, the cause for the recumbency was identified: A mutation in a gene responsible for the calcium exchange in the skeletal muscles and thus for the signal transmission came into focus. It is suspected that in a few cases in addition to the responsible mutation, certain environmental factors must also coincide to lead to the recumbency in calves. Only then the muscle weakness becomes apparent in homozygous animals.In practice, this means that even if the genetic condition of sire and dam was transmitted to the calf at the same time, some calves will not show any sign of the disease. The recessive inheritance of this genetic defect does not show complete penetrance in its expression.

Southwind, born in 1984, seems to be the first bull with this mutation. He spread his causal variant via his offspring (including the bulls Supersire and Robust) in the Holstein population. Since inbreeding is often avoided over a few generations, an accumulation of recumbency cases occurred a few generations later. Only then the chance of the causal mutation coming together is likely from both the maternal and the paternal side.

BLIRD - Low-growth calves and a higher rate of premature calf deaths

The genetic trait called BLIRD (Bovine Lymphocyte Intestinal Retention Defect) is the result of a mutation in the bull Bell Elton. His grandson, the bull O-Man, seems to have been the main propagator of this mutation.

It affects an important gene responsible for the immunity of calves and manifests itself by a defective retention of T-cells (important part of the immune system) in the gut. One consequence of BLIRD is, for example, a reduction in the ability to fight intestinal parasites.

Homozygous BLIRD calves can be born alive. Affected animals show an average growth retardation of about 27% and a 10% higher mortality rate or premature culling in young animals compared to healthy calves.

How often do CALF RECUMBENCY and BLIRD occur?

Recumbency and BLIRD are inherited recessively. This means, both causal allele variants of the gene must be present in the gene pool of the individual for the described phenotype to be expressed. In other words: Only homozygous animals show symptoms. Heterozygous animals, which have both a healthy and a mutated allele version of the gene in their genome, do not show any symptoms. However, these so-called carriers can pass on the mutated allele of the gene to their offspring with a 50% probability, see Figure 1.

The causes of both abnormalities reside in different, mutually independent gene loci. Calves can therefore be carriers or homozygous free for BLIRD or Recumbency.

Figure 1. Recessive inheritance for recumbency. When carrier animals are mated, 25 % of the calves born can be homozygous for Recumbency. This shows up phenotypically in calves unable to stand up and remain standing on their own. The heterozygous carriers (50% of all calves in risk matings) and all homozygous free calves (25 %) of the parents show no symptoms. BLIRD is also inherited recessively. In this case, homozygous calves show a growth retardation ("stunted") and have an increased premature culling rate compared to healthy calves.

Regarding to the frequency of these anomalies, the first studies show a prevalence of 0.3% of homozygous BLIRD calves in France and around 0.1% Germany.

Since the BLIRD mutation was discovered by a French research team, testing and publication of results will be possible by genotyping in laboratories using the EuroG MD chip, such as IFN Schönow and LABOGENA. The mating program will be updated to avoid risk matings and the occurrence of homozygosity.

Recumbency was diagnosed at Pennsylvania State University in the United States. Genetic testing has only recently become available, so it is not possible to make an accurate statement about the prevalence of the defect in the Holstein population at this time. The goal is to determine the genotype for recumbency and implement routine testing for the female population within the following months.

How can the occurrence of BLIRD or RECUMBENCY be avoided?

The occurrence of homozygous calves for these two traits can be reduced by avoiding to mate carriers. This has been done successfully in the past for other genetically undesirable traits. But for this the genotypes of the parents must be known.

All relevant bulls at SYNETICS will therefore be genetically tested and their results considered as soon as reliable tests will be available. If reliable markers have been established on the EuroG MD chip, the genotypes of the females from herd genotyping can also be used and considered in the mating planning. This may take a few more months to ensure the reliability of the test results. We will keep you informed about the ongoing investigations and new findings.

What can I do until then?

The reporting of malformations or abnormalities in calves that have no explainable cause and may possibly be inherited is done in our breeding area on a voluntary basis by the member farms. It is an important contribution to the detection of genetic undesired traits. All reports are gathered and in case of a frequent occurrence of the same reporting or the same pedigree further investigations will be carried out.

Reports can be made by reaching out to your SYNETICS contact person.

You are welcome to report any suspicious calves, including those that do not stand up on their own and may likely be affected by “calf recumbency”, or calves that show significant growth retardation compared to the others or that have died precociously. This will give us the opportunity to examine the incidence of BLIRD and calf recumbency more accurately in the population, as well as their distribution.

How SYNETICS will manage these genetic diseases?

To manage the appearance of BLIRD and Recumbency SYNETICS decided to practice two ways:

1. Testing the whole bull park and publish a list of the testing results on our website to be transparent to our customers.
2. Avoiding the purchase of BLIRD and Recumbency carrier bulls in the future.

Sources:

BLIRD
Press release Prim‘Holstein, France, 31.8.2022
vit Informationsveranstaltung ZWS Milchrind 15.03.2023

Recumbency
Dechow et al. (2022): Identification of a putative haplotype associated with recumbency in Holstein calves. JDS Communications 3:412–415, 10.3168/jdsc.2022-0224
Dechow: Mutation sometimes leads to calf recumbency. Hoard’s Dairyman.