Essay/Term paper: Twinning in cattle

Essay, term paper, research paper:  Science

Twinning in Cattle


Mac Winslow
Dr. Farin
ANS 220 3
December 1996

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 how 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 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 was 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 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.
"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 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 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 several 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 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 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.