The sex ratio and multiple births in cattle¹)

Effects of dam and sire group on the propensity for twin calving in cattle

“…The intention is to avoid the possible confusion introduced by other authors such as Bowman and Hendy (1970) who refer, for example, to the 'effect on dam performance of twinning in British Friesian cattle', where we believe that they meant 'cow' rather than 'dam' performance. The well known Swedish scientist, Johansson (1932), also used in English the term 'twin mothers' to refer to what we describe as 'twin-calving cows'. Stolzenburg and Schonmuth (1979), referring to 'Zwillingsmuttern' as 'twinning mothers', where we believe that they meant 'twincalving cows'.…”

Genetic Variation in the Frequency of Multiple Births in Cattle

“…Earlier investigations, carried out on cattle as well as on several other animal species and in man, have shown that the age of the mother influences the frequency of multiple births (JONES and ROUSE, 1920; BONNEVIE and SVERDRUP, 1926; DAHL-BERG, 1926; HEWITT, 1934;WEINBERG, 1928, etc.). As this has been proved also to apply to the material presented here (JOHANSSON, 1932;KORKUAN, 1946), the variation caused hereby was principally eliminated by the fact that in the Finnish material, which comprises calvings during a limited number of years, the cows were divided into groups each including cows born within three successive years. In the Swedish part of the material the cows were divided into groups with equal number of calvings per cow within the groups.…”

“…Several authors (e. 6. JOHANSSON, 1932;HEWITT, 1934;WEBER, 1944; KOBKMAN, 1946) have proved that the frequency of twin births increases with the age of the animals. This is true at least as far as to the ninlh calving.…”

Studies on Sheep Production Records

“…Results reported by Johansson & Hansson (1943), Young et al (1963) andCh'ang &Rae (1970) indicate that the heritability for fertility is lower for 2-year-old ewes than for older ones. Hallgrimsson (1966) found the highest heritabilities for number of lambs at 3 years of age, although no significant differences between the age groups could be found.…”