PROBLEMS IN BREEDING

New Zealand Herald, Volume LXXI, Issue 21765, 3 April 1934, Page 14

PROBLEMS IN BREEDING

SEX RATIO IN CALVES Investigations carried out at the Wisconsin University Agricultural Experiment Station by Ivar Johansson, of Sweden, in co-operation with L. J. Cole, Professors of Genetics, show that the belief that certain bulls or cows" have a, specific tendency to produce a preponderance of male or female calves is incorrect. The research work of these men shows clearly that such variations in the sex of calves from particular parents are due to chance alone. The study was based on a large number of carefully-compiled private herd; records of three Swedish breeds of cattle —Swedish Eed and White,' Swedish Friesian, and Swedish Landraces (the native Swedish cattle) —and also East on data obtained from the herd books of the Finnish Ayrshire breed and the East and West Finnish Landrace breeds. The births that were tabulated and classified totalled over 124,000.

It was found that the normal ratio of male calves born was 10G.2 to every, 100 females, with no significant variation in this respect between the various breeds studied. This ratio checks closely with data secured by other investigators based on studies with breeds of cattle kept in tho United States. Another discovery was that there is no significant tendency for a cow or bull to have more heifer calves when a particular parent is young or relatively old. The ratio between male and female calves remains practically constant regardless of the ago of the cow or of the sire. The season of the j - ear when the calf is born likewise has 110 effect in determining the sex. Twin calves, on the other hand, are more likely to bo females than males. On the average there are only 96.34 twin calves of male sex for every 100 that are females. This lower ratio of male calves in instances of multiple birth is probably explained by the larger number of male young that are born so early in the gestation period that they fail to live. It has been demonstrated that in the case of abortions and stillbirths with many species of mammals, as well as cattle, appreciably more males than females are expelled from the uterus prematurely or dead. Data secured in this investigation indicate that with aborted calves the ratio is 14'1.07 males for each 100 females. Tho conditions in the maternal uterus thus seem less favourable for a male faetus than for a female. This study has confirmed the common observation that twins are less rugged and strong than calves born singly, so it is natural to suppose that a larger than normal number of male calves will be expelled prematurely from the uterus when the cow is carrying twins. This result would correspondingly increase the ratio of twin calves carried tho full term which are of the female sex, due to the selectivo early mortality of the male calves.