Dexter Cattle Association
January 14, 2009
fact sheet addresses the most commonly asked
questions about a genetic defect that has recently
been confirmed by DNA testing in several breeds
of cattle, including Dexters. The questions
and answers presented herein are based on the
conclusion that Pulmonary Hypoplasia with Anasarca
(PHA) is the result of a mutation in a specific
gene on cattle chromosome 6. Dr. Jon Beever,
of AgriGenomics, Inc., has developed a genetic
test that identifies the presence of the mutation
in this specific gene.
What is Pulmonary Hypoplasia with Anasarca (PHA)?
refers to the lungs, and “Hypoplasia”
means incomplete formation; thus “Pulmonary
Hypoplasia” means incomplete formation
of the lungs. “Anasarca” means a
general accumulation of serum fluids in various
tissues and body cavities; thus anasarca results
in swelling and a swollen appearance. In order
to be PHA-affected, a calf must inherit a PHA
gene from both its sire and dam. Since the PHA
gene is recessive, the lethal form of this condition
is only expressed when the calf is homozygous
for the PHA gene. PHA-affected calves are either
aborted or stillborn. Because of the anasarca
that is associated with this condition, the
PHA-affected calf may also swell tremendously
with fluid, making delivery difficult and potentially
endangering the life of the cow.
2. What is a gene? What is the difference
between a gene and an allele?
A gene is a sequence of DNA which provides the
basic instructions or “code” for
a certain trait or function. Genes are the basic
units of the hereditary information that is
passed from one generation to the next, and
they can have alternate versions. The alternate
versions of any specific gene are called alleles.
Genes occur in pairs. For each pair of alleles,
one is inherited from the sire, and one is inherited
from the dam. Alleles can be dominant, co-dominant,
or recessive relative to each other. The allele
for PHA is recessive to its normal, non-mutated
allele. The PHA allele does not have the normal
sequence and number of base pairs needed to
code properly for its functions. Since alleles
occur in pairs, an animal that has one PHA allele
and one normal allele will be not be affected
by PHA, but it will be a carrier of PHA. Since
the normal allele is dominant, it will code
properly for its functions and normal development
of the lungs will occur even if the animal is
a carrier of the PHA allele.
3. What is a mutation?
A mutation is a spontaneous change in the DNA
sequence that makes up a gene. Mutations can
range in size from a single DNA building block
(a base pair) to a large segment of a chromosome.
PHA mutation in Dexter cattle occurs in the
same gene as the PHA mutation in Maine-Anjou
and Shorthorns, but it is a different change
in the DNA sequence, so it is considered to
be a different mutation. It results in the same
outcome because the same gene is damaged and
cannot perform its intended function.
4. Is PHA in Dexters due to a recent
We don’t believe so, but the ability to
conduct a DNA test for the PHA mutation is very
recent. The Journal of Anatomy and Physiology
in Great Britain, published in 1906, page 293,
references the following: “Lesbre and
Forgeot describe another achondroplasic calf
which was born dead in an extraordinarily anasarcous
condition.” Since Lesbre and Forgeot were
dealing with “bull-dog” calves that
were found only among the pure Dexter-Kerry
breed, they may have confused a PHA-affected
fetus with a Chondrodysplasia-affected fetus,
or it may have been a fetus affected by both
The first publicly-identified PHA carrier in
the Dexter breed is Trillium Chabotte, ADCA
#3168. His semen was tested in Australia, and
the test result was reported through Dexter
Cattle Australia, Inc. on December 5, 2008.
This bull was born in Canada in 1985. He was
collected for artificial insemination, and his
semen was used in Canada and exported to Australia.
Although Chabotte has only 9 ADCA-registered
progeny, according to the ADCA Online Pedigree,
as of January 14, 2009, he has more than 3400
descendants in the ADCA registry.
What is a PHA-affected calf?
PHA-affected calf is a calf born dead with underdeveloped
lungs (Pulmonary Hypoplasia) and swelling caused
by excessive fluid retention (Anasarca). When
genetically tested, this animal has two alleles
for the PHA mutation, so it is termed homozygous
What is a PHA carrier?
PHA carrier is an animal that has one PHA allele
and one normal allele, so it is termed heterozygous
for PHA. A PHA carrier Dexter appears normal,
and there is nothing in its phenotype (appearance)
that indicates it is a carrier of the PHA mutation.
Can an animal be a non-carrier of Chondrodysplasia
and still be a PHA-carrier?
the two genetic conditions are not related to
each other. Two different tests are used to
determine the status of these two unrelated
genetic conditions. An animal can be a carrier
of both mutations, or it can be a carrier of
one or neither of them.
Can a “bulldog” calf also be a PHA-affected
a severely affected Chondrodysplasia (“bulldog”)
calf can also be a PHA-affected calf, but only
if it is homozygous for both mutations.
dead, deformed Dexter fetus that may be difficult
if not impossible for a layman breeder to discern
which condition, if either or both, lead to
its death. Other factors may result in aborted
or stillborn calves, so those factors should
not be ruled out without a DNA test of the fetal
tissues to confirm its PHA and Chondrodysplasia
If a bull sires a PHA-affected calf, what does
a bull sires a DNA-confirmed PHA-affected calf,
it means that the bull is a PHA carrier and
that the dam of the calf is also a PHA carrier.
If a cow has a PHA-affected calf, what does
a cow has a DNA-confirmed PHA-affected calf,
it means that the cow is a PHA carrier and that
the sire of the calf is also a PHA carrier.
If I’ve never had a PHA-affected calf,
does that mean that my cows are non-carriers
a cow’s status as a non-carrier of PHA
can only be determined by genetically testing
How do I test to determine the PHA status of
ADCA is actively promoting PHA testing of all
Dexter AI bulls to build the initial knowledge
base needed to determine the extent or potential
extent of the number of PHA carriers that may
currently exist and to allow breeders to make
informed decisions regarding their own breeding
programs. This is a recently developed test,
and, at the present time, only semen or blood
samples can be tested in the United States.
The ADCA hopes that a test procedure that uses
tail hair samples will soon be available.
submit semen or blood samples for testing: Click
here for the instructions and test application
instructions and application form may also be
obtained from the DNA Testing link on the ADCA
website. Please note that semen samples from
half of the approximately 75 ADCA AI bulls have
been submitted for testing by members of the
ADCA’s Genetics and Pedigree Committee
(GPC) and by others who have volunteered to
submit samples. Some of these bulls have already
been tested in Australia. Owners of past or
present AI bulls who are willing to participate
in the testing program are encouraged to contact
John Potter of the GPC by email (email@example.com)
with the name(s) of the bull(s) which you are
volunteering to test. Owners of recently- or
currently-advertised AI bulls are being contacted
if the GPC does not yet have samples from those
What can happen when a PHA carrier is bred to
another PHA carrier?
time a PHA carrier bull is bred to a PHA carrier
cow there is a 25% probability of producing
a dead PHA-affected calf, a 50% probability
of producing a live calf that carries the PHA
gene, and a 25% probability of producing a live
calf that is a non-carrier of the PHA gene.
What can happen when a PHA carrier is bred to
a PHA non-carrier?
time a PHA carrier is bred to a PHA non-carrier
there is a 50% probability of producing a PHA
carrier calf and a 50% probability of producing
a PHA non-carrier calf. You will not produce
a PHA-affected calf if you breed a PHA carrier
to a PHA non-carrier.
What are the recommended “best practices”
to breed the Dexters in my herd that are confirmed
to be PHA carriers and conserve their desirable
with any trait, PHA can be managed in a sensible
manner. Dexters, like all cattle, can be bred
in a careful and deliberate program to eliminate
any undesirable trait. The ADCA recognizes and
respects the concept that there is no need to
“throw the baby out with the bath water”
with respect to any trait that has been identified
in our breed.
PHA carriers only to PHA non-carriers.
Test any calves that you produce from PHA carrier
animals to determine their PHA status if you
intend to retain or sell them as registered
breeding stock. Make careful selections based
on that knowledge.
prospective buyers of the PHA status on any
registered breeding stock that you offer for
Retain the offspring that are PHA non-carriers
that have the desired traits you wish to propagate
within your herd.
Gradually replace your PHA carriers as they
become old and unproductive with their carefully
selected PHA non-carrier progeny.
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