Page 21 - Te Mania Angus 2021 Catalogue eBook

WHY BVD / PI TEST? RECESSIVE GENETIC CONDITIONS

Information on undesirable genetic conditions, Arthrogryposis Multiplex (AM), Neuropathic Hydrocephalus
(NH) and Contractural Arachnodactyly (CA) and Developmental Duplication (DD)

All breeds of cattle have undesirable genetic conditions. Fortunately with today’s DNA technologies those in
Angus cattle can be managed.

What are they?
(AM) Arthrogryposis means ‘curved or hooked joints’. Multiplex indicates there are multiple abnormalities
associated with the condition. Animals with the Neuropathic (NH) condition have a large head. Both AM and
NH affected calves are born dead. Calves affected by Contractural Arachnodactyly (CA) are born alive and
can reproduce. Muscle contractures restrict the movement of joints, particularly in the hind legs. Abnormal
muscle contractures decrease dramatically as the calf ages but muscle development always remains poor.
Developmental Duplication (DD) is also referred to as polymelia. Many affected animals are absorbed in utero
or aborted early in gestation. Those that survive to birth typically have additional limbs (usually extra front legs)
originating from the neck or shoulder region. The number of reported cases of AM, NH, CA and DD calves
is very low and there is certainly no need to panic.
How are the conditions inherited?
Both the sire and the dam need to be a carrier (carry one copy of the gene each) to have progeny that have
two copies of the recessive gene. Only a few pedigrees are carriers of the recessive gene.
Two copies of the undesirable gene need to be present before the condition is seen; in which case you may
get an abnormal or dead calf. Animals with one copy of the undesirable gene (and one copy of the normal
gene) appear normal and are known as “carriers”. Carriers, will on average, pass the undesirable gene
onto a random half (50%) of their progeny. When a carrier bull is mated to a carrier cow there will be a 25%
chance that the progeny produced will have two normal genes. There will be a 50% chance that the mating
will produce a carrier and there will be a 25% chance that the progeny have two copies of the undesirable
gene and the calf will be abnormal. For the condition to be expressed the undesirable gene needs to be
present on both sides of the pedigree and both the sire and the dam need to be a carrier.

A DNA-based test has been developed which determines whether an animal is a carrier or free of the AM, NH
or CA gene. After DNA testing animals are classified in these categories:
AMF, NHF, CAF or DDF – Tested free of the undesirable gene
AMC, NHC, CAC or DDC – Tested as carriers of the undesirable gene
NZ Angus uses sophisticated software to calculate the probability of all untested animals on their database to
be a carrier and this is reported as a percentage susceptible. The categories are:
AMS%, NHS%, CAS% or DDS% - Suspected carrier. % = level of suspicion
Animals free of the defect by pedigree and are untested are given the following categories:
AMFU, NHFU, CAFU or DDFU – Free by pedigree, untested

What genetic statuses are acceptable to you will depend on the genetics of your cow herd
You need to take into consideration the bulls you have used previously, whether you have a straight breeding
or cross-breeding enterprise and whether you will retain female progeny for breeding.

Te Mania are being proactive and transparent in managing these genetic conditions, endeavouring to
provide the best information available. Now all sires used are clear of these defects. The greatest risk to the
commercial sector from these undesirable genetic conditions comes from unregistered bulls with unknown
genetic background.

19