Due to the continual fluctuation of the cattle market cattle producers have been searching
for ways to improve their production and increase their profits any way possible. For
years genetic engineers have been working hard on improving economic efficiency in
cattle. It is their hope that through genetic research they can improve the yield and the
income of cattle producers around the world. Research has shown that twinning is one way
that farmers can increase their yield . Twinning has a significant influence on producers
as well as people who are involved in all realms of agriculture. The reason for this
large impact at this time is the fact that the occurrences are limited. However, many
producers have a vision that twinning can be more than a once in a blue moon occurrence.
These producers see twinning as a way to dramatically increase their yield per calving
season. Producers will increase their income due to more weight per year per cow. It is
necessary ;however, that the producer be well educated on ho
w to handle twinning, in order for it to be successful for them.
Many agencies see twinning as an economic move upward. The American Breeder Service has
made efforts to produce semen as well as embryos with high predicted breeding values
available to producers. They have been recorded based on
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twinning probabilities and ovulation rates. A large amount of work on twinning has also
been done by the Meat and Animal Research Center. Since the early eighties, they have
located cattle with a high frequency of twinning and been forming a breeding foundation
based on this characteristic. "We believe the time has come to make some of these unique
genetic resources available to the beef industry through artificial insemination and
embryo transfer" (Gregory 23). An extensive amount of research has been done using embryo
transfer in cattle. In one study recipients were implanted with either a single embryo,
two embryo in one uterine horn, or one embryo in each uterine horn. It is also possible
to split embryos using a micro manipulator and implant each half to produce identical
twins. On the average about 16% of the cows implanted with two embryos produced twins.
When two embryos were implanted, and one was placed in each horn, conception rates were
comparable with the prior method, however the twinning rate wa
s much higher when the embryos were in separate horns (73% vs. 45%). For the most part,
when one embryo was split in an attempt to produce identical twins, only one of the
offspring survived birth (Davis 302).
Many producers see twinning as a possible advancement in economic prosperity for
themselves. Scientists have increased the possibility of successful twinning through
extensive genetic research. They now also able to inform the producer of twins through
the use of proper palpation techniques as well as ultrasound. Blood can be analyzed in
labs to determine fetal weight gain. In addition nutritious feeds and technology that
aids in calf survival have made the possibility of
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high twinning success rates closer to being reality. These factors enable the genetic
possibilities to be an asset to producers (Gregory 23-24).
"Increased frequency of twinning should increase efficiency of beef production" (Davis
301). Results from twinning are very appealing to a farmer who can use one brood cow to
produce two calves per year. Reports show that beef cattle can wean a higher total weight
per cow. A twin's average daily gain depends on the environment as well as genetics
(Cady 950-956). Single born calves are reported to have birth weights of 25% more than a
twin calf. Over time, however, the twin calves approach the weight of the single calves.
At weaning the weight gap decreases to only about 15%. Despite this seemingly large
difference in weaning weights, it should be realized that there are two calves to sell
from a set of twins as compares to one from a single birth. In addition to their size,
twin calves consume less rations of fees than their counterparts. From these conditions,
promise for economical stimulus is easily seen, especially in beef cattle (Cundiff
3133-3135).
Despite all of these draw backs, work is being done to help twinning become profitable,
instead of problem causing. A gene has been researched that causes twinning in cows. This
gene could be selected for through expected progeny difference scores just like someone
might select for birth weight. This gene would not only make the offspring of the bull
more likely to have twins, but it would also help her to be maternal to both of the
offspring instead of nurturing one of them and abandoning to other one.
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"At the present, selection for more twin births in dairy cattle results in deleterious
effects on the dams" (Berepoot 1044). Economic calculations have mainly been done on beef
cattle so far. The calculations for beef cattle is mainly centered around final sale
weight per calving season, rather than milk production as in dairy cattle. (1044). Dairy
cattle producers usually discourage twinning because of milk loss. Twinning may be
directly related to high lactation. Dairy cattle that have superior milk production tend
to have higher twinning rates. Even though these cattle were superior in milk, they gave
less total milk. An increase in hormones which will inhibit lactation may explain the
decline in milk production. Thankfully, this milk decrease does not effect the lactation
results of the dam in future parturitions. Since the return of estrus these dams takes
longer, there is added milk loss due to loss of productivity (Syrstad 255-261). "in
general, there were so many disadvantages that attempts to select
for more twin calves in dairy cattle herds should be discouraged" (Beerepoot 1051).
Twinning in cattle has many positive and negative effects. These effects depend on the
breed of cattle and the purpose for which the cattle are raised. Producers can move
forward in today's economy through the successful use of twinning. However, the producer
must be ready, willing, and able to deal with the difficulties that con along with
twinning, in order to ensure the survival and success of not only the calves but of the
dams. Selective breeding methods can be utilized to chose a base herd for a twinning
program. At this time, many producers believe that the negative effects outweigh the
benefits. Through continuing research in the area, twinning shall become
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a successful and economic way to raise beef cattle. Since twinning research began, the
percentage of beef cattle giving birth to twins has risen by nearly twenty percent.
Through research and education of producers twinning could be one of the beef industry's
greatest reproductive achievements.
Twinning is often associated with major management problems, such as an increased
frequency of dystocia, retained placenta, and longer rebreeding intervals."Dystocia is
defined as all calvings for which personal assistance is needed, and dystocia depends on
the size of the calf, its sex, and the age of the dam"
(Beerepoot 1048). "Dystocia accounts for most calf deaths within the first 24 hours of
calving" (Taylor 233). Twin calves have a 15% greater chance of undergoing dystocia and
the chance of a free martin offspring is likely (Hays and Mozzola 7). Twins have only a
8% less chance of survival, even when there is dystocia. "Twinning has not been
considered [in the past as] desirable in cattle because of increased incidence of
retained placenta, reduction in future reproductive efficiency, weaker calves that are
more difficult to raise, and reduced milk production by the cows after twinning" (Bearden
100). A cow that retains her placenta has a greater chance of infection and a longer
duration before returning to estrus. Cattle producing twin calves are estimated to remain
open 19-22 days longer than single calvers (Chapin 1-6). The length of gestation in a cow
is, on the average, is seven days shorter in cows birthing twins than is cows that are
birthing singles (Gregory 3135). This can result in a significant loss
in the number of offspring and the quantity of milk a cow can produce in her lifetime.
Twin
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calvers can also be costly due to the fact that they are subject to different postpartum
nutritional needs (Cundiss 3133).It has also been observed that there is an increased
incidence of abortions during late pregnancy among cows that carry twin fetuses.
"The heritability of twinning is lower. A higher incidence of twinning has been reported
for certain cow families, but long term selection studies to increase twinning have not
greatly increased the twinning rate" (Bearden 100). In many analysis, repeatability was
estimated to be less than heritable, this is assumed to be due to small negative
environmental covariances in adjacent gestation or estus cycles (Gregory 3214). The
genetic correlation between ovulation rates and twinning were found to be 80% in cattle.
Yet, in heifers it had a substantial increase of 10% more. Research by recording
consecutive ovulation rates, can help when establishing a base herd with emphasis on
twinning. Using these records, producers can have a hold on relative twinning. Sires may
also be selected based on the same records from their daughters (Gregory 3212-3218).
Ovulation rate in heifers can be used to predict breeding values for twinning. To pick
breeding values a producer should use the average ovulation rate form severa
l estrous cycles. Estrous cycles can be observed at
3 week intervals between puberty and breeding. In recent test analysis genetic
correlation proved to be high with twinning. The analysis was not independent because it
had many cows and several estrous cycles.
"Adjustments in management practices are required to exploit full potential of twinning
to increase efficiency of beef production" (Gregory 3134). Twin carriers need
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a great deal of care to ensure a safe gestation period and a safe delivery. Recently more
producers have began to use ultrasound to detect the number of embryos, fairly early in
gestation. This saves the producer a great deal of money that would other wise be lost,
because paying a veterinarian is much more economical than loosing two calves. More
postpartum care is also required for the mother and the offspring by the producer. Many
times when a cow gives birth to a pair of twins her maternal instinct only tells her to
take care of one of the calves. Due to this one of the offspring is abandoned and given
no care from the dam. This leads to the death of the abandoned offspring.
Even though good breeding practices have proven to be a major factor, the environment
will also have a large influence on twinning. Part parity seems to have the largest
effect, not considering heritability. One percent twinning was displayed in cows in their
first parity. Yet, 6% twinning was displayed in cattle in their third parity. This could
be directly related to the cattle's age and the ability of the cow to maintain a biparous
pregnancy. Time is a large factor in beginning and maintaining a herd that is prone to
having a large twinning percentage. Genetically, twinning is not affected largely by
additive variation (Cady 952-956). Age of the mother does not usually affect the
proportion of twins born alive; however, the frequency of natural twinning increases with
age and parity of the dam (Davis 306). Most twinning research has been done on
crossbreeds, which is not a true estimate of all cattle because of possible hybrid vigor
concerning certain traits. Not much research has been done on
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in-breeding and between breeds. More will be learned about the genetic variation
responsible for twinning, once these ideas have been researched more.
Works Cited
Davis, M.E.; W.R. Harvey; M.D. Bishop; W.W. Gearheart, "Use of embryo Transfer To
Induce Twinning in Beef Cattle:Embryo Survival Rate, Gestation Length, Birth Weight
and Weaning Weight of Calves". J. of Anim. Science, 1989. 67: 301-310.
Cundiff, L.V.; Gregory, K.E.; Echternkamp, S.E.; Dickerson, G.E., "Twinning in Cattle
III. Effects of Twinning on Dystocia, Reproductive Traits, Calf Survival, Calf
Growth, and Cow Productivity." J. of Anim. Science, 1990. 68:3133-3144
Bearden, J.W.; M.D. Holland, K.L. Hossner, J.D. Tatum. "Serum Insulin-Like Growth
Factor I Profiles In Beef Heifers With Single and Twin Pregnancies". J. of Anim.
Science, 1988.66:3190-3196.
Cady, R.A., L.D. Van Vleck, "Factors Affecting Twinning and Effects of Twinning on
Holstein Dairy Cattle." J. of Anim. Science, 1978.46.950-956.
Taylor, Robert E. Beef Production and the Beef Industry. 1984 Burgess Publishing
Company. Minnaepolis.
Gregory, J.E. Reproduction in Farm Animals. 1980. Lea & Febinger. Philedelphia
Beerepoote, R.H. Reproduction of Farm Animals. 1982. Logman Inc, New York
Russell, Perter J. Genetics. 1996. Library of Congress, Washington DC.
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