No abstract

A statistical investigation has been made comprising 12 European cattle breeds with a total of about 5.3 milj. calvings and 120,000 twin births. Season of conception has a marked influence on the frequency of twin births, one maximum corresponding to spring and another one to autumn conceptions. There are significant breed differences in the relation between age of the cows, measured in parities, and the frequency of monozygous (MZ) as well as dizygous (DZ) twin births. On an average, the DZ frequency increases more than the MZ frequency from the first to the fourth‐fifth calving; then the age‐curves show a plateauing tendency. After the first twin birth, the twinning frequency at the following calvings is 4–5 times higher than in the general population. Apparently, twinning depends on polygenic inheritance and also on various environmental influences, with a threshold for the phenotypic manifestation. It may be assumed that the underlying liability of the cows in a population to bear twins has an approximately normal distribution. The heritability of twinning has been estimated on the binomial p‐scale as well as on the x‐scale of the normal curve. On the p‐scale the heritability of twinning was found to be about 0.02 which corresponds to 0.16 on the x‐scale, although with some differences between breeds.

No abstract

No abstract

No abstract