inheritance of horns and scurs is much simpler
than other genetic traits such as growth, fertility,
feed conversion and carcass traits because so
few genes are involved. However, there have
been few research resources allocated to defining
the specific inheritance of these traits. We
know a lot about them but we are not absolutely
sure about all aspects of their inheritance.
this article, I will discuss the inheritance
of horns and scurs (or the lack of them) and
list specific ideas that might be used in your
selection and mating decisions. I will identify
some areas of the inheritance that we are not
sure about, but emphasize the most likely inheritance
where there is doubt.
Errors in classification have impeded research
efforts as well as limited progress in selection
programs. On one end of the spectrum, you must
differentiate between smooth polled cattle and
cattle that have very small, almost undetectable
scurs. At the other extreme, we must distinguish
between heavy scurs and horns. Errors in classification
can not be scurred unless they are hornless
because the horned condition covers up scurs.
Horned animals can have zero, one or two scur
genes but we never see the effect of the scur
gene until we produce a hornless animal.
are defined as horny tissue which are generally
loose and moveable but may become attached to
the skull in older animals. There is great variation
in the size and growth rate of both scurs and
horns, but males generally develop scurs and
horns faster than females.
preweaning ages, horns are also loosely attached,
especially on heifers. Consequently, breeders
or researchers that classify calves at young
ages are likely to make mistakes. Those mistakes
can be corrected if you leave the scurs intact
rather than removing them. If they are really
horns, it will usually become clear as they
get older. Seedstock producers should be trying
to identify genetic differences in their cattle.
In my opinion, breeders should not remove scurs
but let them develop so that you know what you
really have. Some females don't even show scurs
until they are 18 months of age or older, and
only a small percentage of scurred heifers have
prominent scurs at weaning time. Most heifers
that have horny tissue that is prominent enough
to justify removing it at weaning are horned,
generally show more prominent scurs than heifers
but there are times when scurs on bulls are
so small, like a small scab, they are hard to
see even on close examination. Careful examination
at 12 months of age or older will usually reveal
scurs on bulls if they are going to have them.
"Careful examination" means that the
bull is restrained, the lighting is excellent
and that you either clip the head or spread
the hair to make sure there are no scabs.
In the simplest explanation, the polled gene
is dominant to the horned gene, and the horned
gene may just be the absence of the polled gene.
A cow or bull with one polled gene would be
hornless but might have scurs. These animals
are categorized as heterozygous polled. When
a heterozygous polled bull is mated to horned
cows, 50% of the progeny will be polled (heterozygous)
and 50% will be horned. If a heterozygous polled
bull is mated to heterozygous polled cows, 75%
of the calves will be polled (25% homozygous
polled, 50% heterozygous polled) and 25% of
the calves will be horned.
with two polled genes would be classified homozygous
polled and should produce only hornless calves
(some of the calves may have scurs).
horned animal has zero polled genes and when
mated to horned cows will produce 100% horned
The inheritance of scurs is more complicated
than that of the polled gene because of sex
differences, the possible existence of other
genes that modify the size of scurs and the
suggested existence of incomplete penetrance
which would mean some animals might have the
genes for scurs but not express them. The expression
of the scur gene is also affected by the presence
of the horn gene since horned animals cannot
show scurs and heterozygous polled cattle (which
have one horn gene) are more likely to be scurred
than homozygous polled cattle.
geneticists think it is likely that all scurred
animals are heterozygous for the polled gene
but this has neither been proven nor disproved
by research. Theoretically, homozygous polled
bulls and females could have scurs if they have
two scur genes, but no one has reported a scurred
animal that proved to be homozygous polled.
Proving the existence of one bull that is scurred
and disputedly homozygous for the polled gene
would establish that scurred animals could be
homozygous polled. >From a practical standpoint,
breeders may be able to eliminate the horn gene
faster by assuming that all scurred cattle are
heterozygous for the polled gene.
females must have two scur (Sc) genes and most
likely have a genotype of PpScSc, but might
be homozygous polled with a genotype of PPScSc.
Scurred bulls that are heterozygous for the
polled gene need only one scur gene to be scurred
(genotype of PpScsn, where sn indicates the
absence of the scur gene). Again, some people
believe that all scurred bulls are heterozygous
for the polled gene but there is no data that
proves it. Homozygous polled bulls (PP) can
carry the scur gene and be smooth polled while
have a genotype of PPScsn. Theoretically, a
homozygous polled bull could be scurred if he
had two scurred genes (PPScSc).
important fact is that any bull that has one
scur gene but is not scurred must be homozygous
polled. Further, any bull produced by a scurred
cow must have the scur gene as does any bull
that sires a scurred heifer.
Applications for Polled Selection:
Many breeders are selecting for the polled trait,
and one of the problems they have is determining
whether a smooth polled animal carries the horn
gene or not. Identifying homozygous polled bulls
is especially important because each calf crop
sired by a homozygous polled bull will have
a frequency for the horned gene that is half
that of their dams'.
most accurate way to identify homozygous polled
bulls is by mating them to horned cows. If you
breed a bull to five horned cows and get all
polled calves, you have a 96.9% chance that
your bull is homozygous polled.
clearly shows that you don't need to breed to
a lot of horned cows to prove a bull homozygous
polled, but more than five is recommended. Ten
polled calves from horned cows gives you a confidence
level of 99.9 percent, and 13 calves gives you
a confidence level of 99.99 percent. You can
also prove a bull homozygous by mating him to
heterozygous polled cows, but it takes more
than twice as many matings to reach the same
confidence level. It is important to note that
one horned calf proves the parents to be heterozygous
previously discussed, you must consider possible
mistakes in classification and possible mistakes
in parentage with horned bull calves. A horned
heifer calf can only be explained by a mistake
in parentage or by the calf getting a horned
gene from both parents. Newborn calves are difficult
to accurately classify, and so it is best to
wait until the calves are at least a couple
of months of age before declaring them polled
and then only after handling their head.
(all possible scur
Abbreviations: P=polled p=horned Sc=scur
closing, it is important to remember that the
polled trait is a convenience trait that is
desirable when combined with profit-making traits.
An inferior polled animal is no more valuable
than any inferior animal.
The following tips and ideas will help identify
the genotype of polled cattle. These are not
guarantees but a compilation of steps you can
practice based on the factors I have discussed,
and they should at least improve your odds of
locating homozygous polled cattle. Tip #4 and
Tip #6 assume that any scurred animal is heterozygous
polled, which has not been proven.
The label double-polled is applied to cattle
when both their parents are polled, and is useful
only if there is no doubt in the accuracy of
how their parents were classified. Double-polled
cattle that produce horned calves have the same
genotype as polled animals that have one horned
Cattle with two polled parents have a one-third
chance of being homozygous polled, and double-polled
bulls that are not scurred have greater than
a one-third chance of being homozygous polled.
A double-polled, non-scurred son of a scurred
cow will be homozygous polled and will carry
at least one scur gene. To count on this, you
must be sure the bull does not have even a scab
A double-polled female that produces a scurred
calf by a homozygous polled bull is probably
heterozyous for the polled gene (Pp).
Any bull, horned or polled, that sires a scurred
heifer carries at least one scur gene.
Scurred cattle are probably heterozygous polled
with a genotype of PpScsn or PpScSc.
Breeding homozygous polled bulls to heterozygous
polled females should produce all polled calves,
and 50 percent of these calves should be homozygous
Breeding homozygous polled bulls to double-polled
females should produce all polled calves, and
two-thirds of the calves should be homozygous
Breeding homozygous polled bulls to polled females
that are daughters of homozygous polled bulls
should produce all polled calves, and three-fourths
of the calves should be homozygous polled.
Breeding homozygous polled bulls to homozygous
polled females should produce all homozygous
polled calves and no scurs.