Twin Calves In Dairy Cattle Herds example essay topic

Mac Winslow Twinning in Cattle 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 Winslow 2 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 an 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 Winslow 3 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. Winslow 4 "At the present, selection for more twin births in dairy cattle results in deleterious effects on the dams" (Beerepoot 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 parturition's. Since the return of estrus these dams takes longer, there is added milk loss due to loss of productivity (Syr stad 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 Winslow 5 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 re breeding intervals". Dystocia is defined as all calving 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 Moz zola 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 Winslow 6 calvers can also be costly due to the fact that they are subject to different postpartum nutritional needs (Cun diss 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 estrus 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 sever a 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 Winslow 7 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 Winslow 8 in-breeding and between breeds. More will be learned about the genetic variation responsible for twinning, once these ideas have been researched more.

Bibliography

Davis, M.E. ; W.R. Harvey; M.D. Bishop; W.W. Gear heart, "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.
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68: 3133-3144 Bearden, J.W. ; M.D. Holland, K.L. Hoss ner, J.D. Tatum. "Serum Insulin-Like Growth Factor I Profiles In Beef Heifers With Single and Twin Pregnancies". J. of Anim. Science, 1988.
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