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The recent discovery of Neuropathy Hydrocephalus (NH) in the Angus breed is a serious situation that breeders and Angus New Zealand are working hard to resolve.

This article explains what NH is, how it is inherited and practical implications. After reading this article it is hoped that you will have a clearer understanding of the risks, what tools are available to manage any identified risks and what actions you can take. It has been written to help you make decisions to effectively manage NH in your breeding herd.

NH has been identified by Br Jonathan Beever of Illinois State University to be a recessive gene defect that can be identified in the still-born calf by a pronounced enlargement of the cranium of the skull, accompanied by an increased volume of fluid in the cranium – water on the brain.

In addition other defects that can be present are; malfunction of the jaw, scattered positioning of the teeth, skin covering the eye/s, absence of properly formed eyelids, or as stated above the most obvious sign in all cases, the massive swelling of the head.

In several situations it causes dystokia and requires draining of the calf’s head in order to get the calf through the birth canal of its mother.

Genetic defects

Nature continually experiments with new genetic combinations. Through mutations nature introduces more variation in a population. This has been important for performance improvements or ensuring adaptability to changing environments. However, sometimes these mutations are not beneficial.

Genetic disorders are a reality in all breeds. In the 1960s, with fewer genetic tools, the Angus breed had a very successful campaign to deal with an inherited genetic defect called mannosidosis.

Breeders should not panic nor take drastic actions because the situation is one that is quite manageable in most cases and one that will be resolved over time.

 

How is the disease inherited?

Research in the U.S. and Australia indicates that NH is a simply inherited recessive defect. This means that a single pair of genes controls the condition.

For this mode of inheritance two copies of the lethal gene need to be present before the condition is seen; in which case you get a calf with NH.

A more common example of a trait with a simple recessive pattern of inheritance is black and red coat colour.

Animals with only one copy of the lethal gene (and one copy of the normal form of the gene), that appear normal, are known as “carriers”

The origin of the NH mutation is the very popular USA bull G A R Precision 1680.

 What happens when carriers are mated to other animals?

If N = Normal gene and n = NH gene then:
NN = normal calf (is normal)
Nn = a carrier calf (appear normal)
nn = NH (dead and deformed)

Carriers, will on average, pass the lethal gene to a random half (50 %) of their progeny.

When a carrier bull and carrier cow is mated (both parents Nn as shown in the below punnet square), there should be a 25% chance that the progeny produced will have two normal genes and consequently will never pass on the defective gene.

There should be a 50% chance that the mating will produce a carrier. However, there could be a 25% chance that the progeny have two copies of the defective gene. Reports from breeders show lower than expected numbers of affected (dead) calves and therefore it appears that there may be some other factors influencing the percentages indicated above. This is under investigation.

If animals tested free of the defective gene are mated to carrier animals the NH condition will not be expressed at all. All calves will appear normal, but approximately half (50%) are expected to be carriers as explained below.

These illustrations highlight that for the lethal defect to be expressed the NH gene needs to be present on both sides of the pedigree and both the sire and dam need to be a carrier.

Identifying carriers of NH is important for effective management of the disease.

The surest and simplest identification of a carrier is that they have a dead and deformed NH calf.

As explained above, for this to occur the carrier cow needs to have been joined to a bull that is also a carrier.

This means that the identified carrier may have had many normal calves, from joinings to bulls that do not carry the NH gene. If a recipient cow has an NH calf, it means both the donor cow and the sire are carriers of the NH gene.

Angus New Zealand (ANZ) will be maintaining a database of animals carrying the NH gene. Breeders are urged to report as a matter of urgency any calf born dead that fits the NH clinical description and do not test positive to Akabane or any other Simbu type virus.

U.S. scientists have identified a mutation that they believe is responsible for causing the condition. Dr Jon Beever is confident that he has developed an accurate DNA-based test that can be used to assess whether an animal is a carrier or free of the NH gene.

A list of test results (2) for New Zealand bred and used animals as well as Australian and American bred animals is published on the ANZ website or available directly from ANZ on request. The NH status of individual animals is now displayed on the “animal details page” on the ANZ website. This information can be accessed by conducting a “Database Search” from the Angus website for a specific animal. NH status web updates will occur each weekend with certificates of animals indicating an animal’s NH status.

Animals that are related to tested carriers (NHC) and have not yet been tested are flagged as NHS (NH-Suspect) on the Angus website. To help Angus breeders determine which animals have a high probability (percentage chance) of being carriers and should therefore be tested, ANZ has sent members a list of all active females in their herds.

Interpreting and using the NH probability lists sent to members

Members have been sent a list of all active female animals in their ownership. The "PROB” column indicates the probability (as a percentage chance) of the animal carrying the NH gene. This list continually updates from test results submitted by members or from overseas and from direct communication with the Australian database. The robustness and accuracy of this information will dramatically change as more results are clarified.

Only animals with a probability of being an NH carrier that is greater than 1 % will have NHS status on the ANZ website. Most people will have a large number of animals with very low probabilities on their list. This is because currently we are not sure how far back the NH defect mutation happened.

Currently RITO 9J9 OF B156 7T26 is the deepest in the affected pedigrees that an NH carrier has been confirmed. The analysis therefore assumes and bases the calculation on the probability that his sire and dam line may have also had the defect. This means that there are a large number of animals deep in pedigrees that could have passed the NH defect gene on to animals in the current Angus population. Scientists are currently testing ancestors of 9J9 to try and determine whether the defect arose in his sire or dam line.

Hopefully this will clear either his sire or dam line and with it a large number of animals that trace back to animals in these lines. In the probability analysis a background frequency of 0.5 % probability in the Angus population has been assumed. This causes the analysis to calculate the probability of an animal being an NH carrier where it does not have any information on any of its ancestors or progeny as 0.996%.

The following guidelines are provided to prioritise testing of suspect animals to confirm their status.

SETTING PRIORITIES FOR TESTING

Which animals should I test first?

-  High impact animals:
-  Sires that will/have been used heavily in your herd
-  Donor cows
-  Animals deepest in the pedigrees (Consider the flow-on effects of determining the status of ancestor
    animals first)         
-  Animals with the highest probabilities of being NH carriers
-  Animals that you wish to sell in the near future

How is AA reporting the NH status of animals?

The NH status of animals is being reported using five categories:

Interpreting the DNA test results

The result, in terms of proportions of progeny with the three possible genotypes, for different matings of normal and carrier animals is shown in Figure 2 below.
Figure 2. Expected progeny NH genotype percentages(NB) for different mating scenarios

NB: The average progeny percentages shown are expected for a large number of animals. The smaller the sample size the greater the likelihood that actual percentages will vary.
NHF animals will not transmit the defect gene to any of their progeny.

An important point is that carrier animals (NHC) are not affected and can be effectively utilised in a breeding program with caution not to mate them to other carrier animals.

Practical implications for Angus breeding programs:

New Angus New Zealand regulations

The Angus NZ (ANZ) Council regulations are being implemented with a short term objective to manage NH but longer term objective to eradicate it from the ANZ gene pool.

The registration certificates and animal details page on the ANZ Internet Solutions database will display a code describing the (NH) status of all ANZ registered animals as described in the following table;

 

NZAA regulations relating to Genetic Defects

1. Only those progeny derived from sires carrying an AMF/AMFU and NHF/NHFU status will be eligible for registration for;

(i) AM progeny born on or after 1st January 2010

(ii) For NH progeny born on or after 1st January 2011

2. Only animals that are AMF, AMFU, NHF and NHFU can be sold with transfer.

3. No clones of animals identified as carriers of AM/NH shall be eligible for registration.

4. Only the results from AngusNZ approved labs will be recognized.  

5. AngusNZ will review these regulations from time to time as new information becomes available.

 

Why do DNA samples preferably need to be sent to PBBnz for Angus New Zealand?

Why do DNA samples need to be sent to the NZ Angus Association office?
It is ANZs experience that a formal procedure for processing DNA samples is essential. This is to ensure quality controls for traceability, security, IP ownership, free sample storage and assurances that increase efficiency, and facilitate future access to the sample(s).

For that reason, it is recommended that all DNA samples be submitted through ANZ.

Therefore on receipt of samples ANZ staff will;

• Verify that the information about the animal matches the ANZ database.
• Verify that the person requesting the test owns or has permission to test the animal.

Then;

• A receipt will be issued to the breeder to acknowledge receipt of the sample.
  
  
• An identification barcode (for security) will be attached to the sample.
  
  
• The sample will be dispatched to the lab for the appropriate test(s) to be run.
  
  
• A receipt will be issued by the lab to ANZ acknowledging arrival of sample.
  
  
• The test(s) will be run and the results to be sent to ANZ for their registry staff to post  results electronically onto the ANZ database, against the particular animal(s).
  
  
• These results are then available on the Angus NZ website through the animal enquiry facility.
  
  
• Through this process the owner of the sample(s) and the identity of the animal is not disclosed.
  
  
• In addition the owner retains lifelong ownership of the DNA sample and has the sample stored at no cost.

 

Key points

Important action list

Glossary

Acknowledgements

Disclaimer

Angus New Zealand advises that the DNA test established by Dr Jon Beever as referred to in this newsletter has not been validated by a third party.  Further, Angus New Zealand advises that the probability list information is based on statistical probability.  Accordingly Angus New Zealand makes no statement, representation or warranty as to the accuracy or completeness of any information relating to the Arthrogryposis Multiplex status of any particular animal disclosed to any person by Angus New Zealand and assumes no liability for any loss, expense, cost, claim, liability or damages whatsoever incurred or sustained by any person relying directly or indirectly on the information contained in this letter and any information provided by  Angus New Zealand relating to the Arthrogryposis Multiplex status of any particular animal.  Further, any person relying directly or indirectly on the information contained in this newsletter or information provided by Angus New Zealand relating to the NH status of any particular animal where all or any part of that information has been sourced from a third party (“the third party”) shall not bring any claim, action or proceedings against the third party for any expenses, costs, claims, liability or damages whatsoever incurred or sustained by that person relying directly or indirectly on the information and in the event that person elects to bring a claim against the third party then that person shall indemnify for Angus New Zealand any liability incurred by arisin Angus New Zealand g from the claim being made against the third party.”

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