8. Conclusion

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 cows.

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 negative traits associated with it.

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 practical to choose bulls based on this.

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 their abilities.
