7.7. Economic outcome and selection

Losses due to the higher incidence of abortions, ketosis (subclinical or clinical), reduced birth weight or stillbirths, mastitis, and problems related to dystocia are all more common in twin calvings. Multiparous cows with dead twins produced less milk than cows with live twins. Compared with dams with singleton birth, cows with twins were 0.78 times as likely to conceive and 1.42 times as likely to die or be culled. Cows with dead twins also had increased time to conception, compared with live twins [63].

This increased cost in the case of multiple births adds up to 40% per cow [64]. In the case of twinning, there is an elevated incidence of pregnancy loss and reduced milk yield along with the number of fertile heifers' required for herd replacement [15].

Total losses were on average \$171 – \$63 = \$108 per twin birth. Realistic changes in input variables could not change this negative outcome to a positive result. Therefore, it was concluded that it is not profitable to select to increase the number of twins in dairy cattle [68].

Dairy cattle breeders could develop strategies to manage twinning based, for example, on ultrasonic examination of corpus luteum and its direct use in selection. While it is obvious when cows give birth to twins, it is much less obvious when cows that would have twins suffer embryonic reduction of one of their embryos. An examination [69] of 770 pregnancies showed 13 cows with 3 or more corpora lutea and 757 with 2 corpora lutea. Of those with two corpora lutea, 464 were carrying twins and 293 were carrying single calves. Subsequently, 69 (23.5%) of the single pregnancies and 132 (28.4%) of the twin pregnancies lost one of the corpora lutea or one of the embryos before day 60. Of the 132 twin pregnancies, 34 (25.8%) lost a corpus luteum together with an embryo (corpus luteum reduction occurred in the ovary on the same side as the horn of the uterus that underwent embryo reduction). As dead embryos and their debris are not detectable when they die in early pregnancy, this represents a "hidden rate of twinning" that we have otherwise overlooked.

Author details

András Gáspárdy<sup>1</sup>

References

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978-963-87942-2-2

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\*, James Sheridan<sup>1</sup>

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

, Melinda Ari<sup>2</sup> and László Gulyás<sup>3</sup>

Twin Calving and Its Connection to Other Economically Important Traits in Dairy Cattle

http://dx.doi.org/10.5772/intechopen.72905

77

1 Department for Animal Breeding, Nutrition and Laboratory Animal Science, University of

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

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

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[2] Csukás Z. Tanulmányok egypetés szarvasmarha-ikreken. Magyar Állatorvosok Lapja.

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

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 associated with twin births.
