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are not detectable when they die in early pregnancy, this represents a "hidden rate of twin-

There is an opportunity to change the incidence of twinning in Holstein cattle when the candidate bulls are provided with a breeding value for twinning rate [70]. With heritability at 8.71%, genetic evaluation of sires is possible [26]. Centered about a mean twinning rate of 5.02%, PTA of sires ranged from 1.6 to 8.0%. Therefore, use of sires with a low PTA for twinning rate can be expected to reduce the incidence of twins. Some increase in income can also be expected with a reduced incidence of twins [71]. From a national perspective, this translates into a cost of \$55 million per year to the dairy industry in the United States, assuming 5% incidence of twins, 10

Trying to make a profit from increasing the incidence of twinning within a herd would be very difficult due to the time and money increase associated with twin births. The benefits of twinning cannot be capitalized on without some degree of cost, either financial or reproductive. This can be mainly seen at parturition and postpartum because of the complications

From all of the studies on the subject, it can only be concluded that the occurrence of twin calving is a double-edged sword, as it is a multifaceted trait with many pros and cons that cannot easily be reconciled. On the one hand, we see the benefits of higher numbers of live calves, and on the other hand, we see decreased fertility in cows after twin calving, leading to higher culling rates and thereby decreasing the total number of calves over the lifespan of the cow. That and the decrease in milk production are clearly very negative traits to have in dairy

However, we see cows that have the highest production value in the herd are predisposed to twinning, and increasing nutritional intake to improve productivity also increases twinning. Obviously, it is in the farmer's best interest to breed and feed his cattle as well as possible to increase productivity and profits. Leading to an increase in the rate of twinning and all the

Decreasing the rate of twinning by using bulls with a low PTA for twinning shows some promise as a method of avoiding all of its negative consequences; however, there are many traits in bulls that farmers may value more such as milk solids or milk yields and so may not be

It is hard to say what the best course of action is for dealing with twin calving. But it is advantageous to be aware of its consequences so farmers can deal with them to the best of

million dairy cows in the United States, and \$110 less income per head.

ning" that we have otherwise overlooked.

76 Ruminants - The Husbandry, Economic and Health Aspects

associated with twin births.

negative traits associated with it.

practical to choose bulls based on this.

8. Conclusion

cows.

their abilities.

András Gáspárdy<sup>1</sup> \*, James Sheridan<sup>1</sup> , Melinda Ari<sup>2</sup> and László Gulyás<sup>3</sup>

\*Address all correspondence to: gaspardy.andras@univet.hu

1 Department for Animal Breeding, Nutrition and Laboratory Animal Science, University of Veterinary Medicine Budapest, Budapest, Hungary

2 National Association of Hungarian Holstein Friesian Breeders, Budapest, Hungary

3 Faculty of Agricultural and Food Science, Institute of Animal Science, Széchenyi István University, Mosonmagyaróvár, Hungary
