Understanding Genetic Condition Status
Genetic condition status results are based on DNA samples provided
by breeders. Herefords Australia makes no statements, representations or
warranties about the accuracy or completeness of any information relating to
the status of a particular animal: and disclaims all responsibility for
information and all liability (including without limitation, liability in
negligence) for all expenses, losses, damages, and costs you may incur as a
result of information being inaccurate or incomplete in any way for any reason.
Genetic condition status results are only displayed for animals that
have been DNA tested for a particular genetic
condition or in circumstances where sufficient DNA testing has been conducted
on animals within the pedigree to make some assertions as to genetic condition
status. In cases where the genetic condition status of an animal is unknown, no
genetic condition status will display for the animal.
Code Explanation
(First two or four characters vary with the genetic condition – i.e. HY,
DL, IE, MSUD or MD)
|
_ _F |
Indicates that the sample submitted for this animal has been
tested and found to be free of the causative
mutation responsible for the indicated genetic condition. This animal is
homozygous free, meaning that it has two copies of the normal variant (or
allele) of the gene. |
|
_ _C |
Indicates that the sample submitted for this animal has been
tested and found to be a carrier of the causative
mutation responsible for the indicated genetic condition. This animal is
heterozygous for the mutation, meaning that it has one mutant allele and one
normal allele. This animal could pass the mutation to approximately half of
its progeny. |
|
_ _A |
Indicates that the sample submitted for this animal has been
tested and found to possess two copies of the mutant variant of the
gene. This animal is homozygous for the mutation responsible for the genetic
condition and in the case of HY & IE, will be affected by
the genetic condition. In the case of DL, the animal will appear normal but
will pass the mutation to 100% of its progeny. |
|
_ _ _% |
Indicates that, based on pedigree information
supplied by the breeder of the animal, the animal has a chance to be
a carrier of the mutation responsible for the described genetic
condition but has not been tested. The higher the indicated
percentage, the larger the chance the animal may be a carrier. To verify the
status of this animal, it is recommended that testing be undertaken prior to
using this animal for breeding purposes. |
|
_ _FU |
Indicates that, this animal has not been tested for
the causative mutation but that both the recorded sire and dam have
either been tested and found to be free, or have a status of _ _FU and are
expected to be free of the causative mutation responsible for the
genetic condition. Herefords Australia gives no guarantee as to the animal's
genetic condition status. |
Understanding
Genetic Conditions
Further details regarding each genetic condition is provided below.
Hypotrichosis (HY) -
Partial to almost complete lack of hair. Affected calves are often born with
very short, fine, kinky hair that may fall out leaving bare spots or areas
particularly susceptible to rubbing. The condition may vary in expression as
the animal matures and is usually less noticeable in older animals. The coat
hair colour will sometimes appear "frosted" or "silverish." The tail switch may also be
underdeveloped. Hypotrichosis is caused by a recessive allele which means that
affected calves will only occur when two carrier animals are mated together.
Hypotrichosis has been reported in the Hereford breed for many decades and is
non-lethal.
Dilutor (DL) -
This is a coat colour abnormality that can be found when a Hereford bull that
is a carrier of the dilutor gene is mated to a black cow. A certain number of
the resulting calves are born with grey, smokey or
chocolate coats (approx. 50%). Diluter is not an abnormality that causes any
issues with calf performance. Dilutor is caused by a dominant allele, which
means calves that are expected to have a black coat colour are born with a
smoke colour coat because the dilutor allele is dominant to the black allele.
Idiopathic Epilepsy (IE) -
Age of onset of first seizure can be variable, ranging from birth to several
months of age. Occurrence and persistence of seizures may be influenced by
environmental stress factors such as temperature extremes or increased physical
activity. Upon initial onset of seizure episodes, individuals will typically
lie on their side with all limbs extended in a rigid state. Manual flexing of
the limbs is possible but return to the extended position occurs after release.
Seizure episodes may last from several minutes to more than an hour. Idiopathic
Epilepsy can lead to death and affected animals have not been known to
reproduce. Idiopathic Epilepsy is caused by a recessive allele which means that
affected calves will only occur when two carrier animals are mated together.
Maple Syrup Urine Disease (MSUD)
– This is a condition which has been identified in
both horned and polled Hereford animals. Affected calves display severe
neurological signs within the first week of life. Typically, affected calves
are dull and will become recumbent by 2 to 4 days of age. Affected calves will
enter a state of terminal opisthotonus, where severe
muscle spasms will cause their head, neck and spinal column to present in an
“arching” position. Maple Syrup Urine Disease is fatal, with affected animals
tending to die as young calves before they are old enough to reproduce. Maple
Syrup Urine Disease is caused by a recessive allele which means that affected
calves will only occur when two carrier animals are mated
together.
Mandibulofacial Dysostosis (MD)
– This condition may result in a facial malformation,
which can include cleft palate, brachygraphic (short jaw) and camplygnathia (crooked jaw or face). Affected calves could
display bilateral skin tags, attached to an unusual bone formation, just behind
the corner of the mouth. Additional skin tags may be present near and/or below
the ears. The calves’ ears are sometimes small and floppy.
Jaw muscles are underdeveloped, and
calves may have an elongated oral opening giving them the appearance of an
exaggerated smile. Affected calves have a sucking reflex but will not suckle
vigorously; calves that display additional cleft palate and/or shortened or
crooked jaws will be further debilitated.
While affected calves are typically born alive, they are not able to
thrive. Mandibulofacial Dysostosis is caused by a recessive allele which
means that affected calves will only occur when two carrier animals are mated
together.
Putting Undesirable Genetic Conditions into Perspective
All breeds of cattle, in fact all mammals including humans, have
undesirable genetic conditions. Fortunately, advances in molecular genetics
have facilitated the development of DNA tests for their management. Breed
Societies are at the forefront of development of strategies to manage
undesirable genetic conditions and seedstock members are leading the industry
with their uptake of this technology.
How are the conditions inherited?
Research in the U.S.A. and Australia indicates that HY, IE, MSUD, MD and
DL have different modes of inheritance. HY, IE, MSUD and MD are simply
inherited recessive conditions, whereas DL is caused by a dominant allele.
Inheritance of
HY, IE, MSUD & MD
Hypotrichosis, Idiopathic Epilepsy, Maple Syrup Urine Disease and
Mandibulofacial Dysostosis are simply inherited autosomal recessive conditions.
This means that a single pair of genes controls each condition. For this mode
of inheritance two copies of the undesirable gene need to be present before the
condition is seen; in which case you may get a calf with HY, IE, MSUD or MD.
Animals with only one copy of the undesirable gene (and one copy of the
normal form of the gene), that appear normal, are known as “carriers”.
What happens when carriers are mated to other animals?
A carrier will, on average, pass the undesirable gene form to a random
half (50 %) of their progeny.
When a carrier bull and carrier cow are mated:
· There is a 25% chance that the progeny produced will have two normal
genes and so will never pass on the undesirable gene.
· There is a 50% chance that the mating will produce a carrier.
· There is a 25% chance that the progeny will inherit two copies of the
undesirable gene and hence be affected by the genetic condition.
When a carrier animal is mated
to an animal tested free of the genetic condition:
· All progeny will appear normal and will be unaffected by the condition.
· There is a 50% chance that the mating will produce a carrier.
· There is a 50% chance that the progeny produced will have two normal
genes and so will never pass on the undesirable gene.
Note that an animal that is tested free by DNA test of the genetic
condition will not pass the genetic condition to its descendants, even if it
has carriers in its own ancestry. Therefore, DNA-tested free animals can be
used in your breeding program with confidence that they are not transmitting
the unfavourable gene to subsequent generations.
Inheritance of DL
Dilutor is caused by a dominant allele,
which means for this mode of inheritance calves that are expected to have a
black coat colour will be affected by the condition if they inherit one or more
copies of the undesirable gene.
The condition will never be expressed
in purebred Hereford animals, meaning that carrier animals may appear normal
but possess either one or two copies of the undesirable gene.
What happens when carriers are mated to other animals?
An animal carrying one copy of the undesirable gene will, on average,
pass the undesirable gene form to a random half (50%) of their progeny. An
animal carrying two copies of the undesirable gene will pass the undesirable
gene to 100% of their progeny.
When a carrier animal is mated to an animal expected to produce progeny
with a black coat colour (e.g. Angus or Fresian
animals):
· In cases where the carrier animal possesses one undesirable gene, there
is a 50% chance that the mating will produce an animal affected by the
condition.
· In cases where the carrier animal possesses two undesirable genes, there
is a 100% chance that the mating will produce an animal affected by the
condition.
When a carrier animal is mated to a purebred Hereford animal tested free
of the genetic condition:
· All progeny will appear normal and will be unaffected by the condition.
· In cases where the carrier animal possesses one undesirable gene, there
is a 50% chance that the mating will produce a carrier.
· In cases where the carrier animal possesses two undesirable genes, there
is a 100% chance that the mating will produce a carrier.
When a carrier animal is mated is mated to a purebred Hereford animal
that is also a carrier of the genetic condition:
· All progeny will appear normal and will be unaffected by the condition.
· In cases where both carrier animals possess one undesirable gene, there
is a 75% chance that the mating will produce a carrier.
· In cases where either of the carrier animals possesses two undesirable
genes, there is a 100% chance that the mating will produce a carrier.
As with HY, IE, MSUD and MD, an animal that is tested free by DNA test
of the genetic condition will not pass the genetic condition to its
descendants, even if it has carriers in its own ancestry.
How should genetic conditions be managed?
There are a range of educational resources available that aid in the
management of genetic conditions from the Southern Beef Technology Services
(SBTS) website.
· A Technical Note titled
“Managing Genetic Conditions” is available. http://sbts.une.edu.au/pdfs/Managing%20Genetic%20Conditions.pdf
· A video presentation of a webinar that was
delivered as part of the “Know Your Genes” webinar course is available.
http://sbts.une.edu.au/Webinars/webinars.html