SEX INHERITANCE.

Waikato Times, Volume 111, Issue 18524, 2 January 1932, Page 16

SEX INHERITANCE.

SOME MYTHS EXPLODED

THOROUGH INVESTIGATION. That certain bulls or cows have a specific tendency (inherited or otherwise) to produce a preponderance of male or female calves tias been demonstrated to be contrary to the facts in a very comprehensive investigation made by Ivar Johansson (Scandinavian American Fellow of the Ultuna Agricultural College), Sweden, who has been in residence at the University of Wisconsin, carrying on his studies in co-operation with L. J. Cole (Genetics). On 'the other hand this research shows clearly that such variations as occur in the sex of calves from particular parents are due to chance alone.

The study was based on a large number of very carefully compiled private herd records of 'three Swedish breeds of cattle, i.e., Swedish Red and White, Swedish Friesian, and Swedish Uandraces (the native Swedish cattle), and also on data obtained from the herd books of 'the Finnish Ayrshire breed and the East and West Finnish I.andrace breeds. The births that were tabulated and clasifled total over 124,000.

It was found that the normal ratio of male calves born was 106.2 to every 100 females, with no significant variation in this respect between the several breeds that were studied. This ratio checks closely with data secured by other Investigators based on studies with breeds of cattle kept In the United States.

No Foundation.

Another popular belief shown to have no foundation was the discovery that there is no significant tendency for a cow or bull to have more heifer calves when a particular parent is young in years or when relatively old. The ratio" between male and female calves remains practically constant regardless of the age of the cow or of the sire. -The season of the year when tho calf is born likewise has no effect in determining the sex. Twin calves on the other hand are more likely to be females than males. On the average there are only 96.3-1 twin calves of male sex for every 100 that are females. The 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 still-births with many species of mammals as well as cattle (it it also true with humans) appreciably more males than females are thus expelled from the mother’s uterus prematurely or dead. Data secured in this investigation indicate that with aborted calves the ratio is 14 3.07 males for each 100 females. The conditions in the maternal uterus thus seem less favourable for a male fetus 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 the full term which are of the female sex, due to the selective early mcrrtallty of the male calves. Twin Calves Undesirable. The birth weight of a twin calf is only 70 to 80 per cent that of a cair born singly, its vitality is somewhat less, and the death rate of twins is noticeably higher. Among the Swedish herds studied, the death rate during calfhood was three times as high for twin calves as for those born singly. Extensive Investigations by Johansson and others have shown that about 02 per cent, of all heifers born as co-twins to bulls are sterile, “free martins.” The carrying of twins seems to be a strain on the reproductive organs of a cow, for the records Indicate that the calving interval immediately succeeding the delivery of twins is on the average, with the Swedish and Finnish breeds, 17. days longer, than the interval immediately preceding such twinning. Twinning in cattle seems to.be an inherited characteristic which may be transmitted by either the sire or the dam, and varies appreciably between breeds and also between Individuals within the breed. Swedish Friesian cattle have nearly twice ns many twins is the Swedish Red and White breed and the Swedish Uandraces (3.35, 1.85, and 1.81 per cent of births respectively for the three breeds being twins). In general, twin calves .are more common among dairy breeds than among beef breeds. Cow’s Ago an Influence. The age of the cow has a projounced influence on the frequency of twinning. Up to the age of eight clnine years there is a steady increase in the percentage of twin calves produced, with a gradual increase thereafter. For instance, in the Swedish Friesian breed only 1.09 per cent of births were twins with cows two to three years of age. 2.38 per cent at three to four years, and a steady increase up to 4.72 per cent at seven to eight years. The age of the bull at the lime of mating has no influence upon the ratio of twin calves born. Cows that have given birth to one set of (wins are much more likely to produce twins subsequently than are cows which have never given birth to twins, but this tendency varies between breeds, thus indicating that all mothers of twins are not genetically alike regarding the character in question. After tho first set of twins, cows of life Swedish Red and While and the Swedish Uandraces were found on tho average |o have another multiple birth in 6.61 per cent of their subsequent calvings. For the Swedish Friesian cows this tendency was twice as great, being 12.69 per cent. gome animals seem to carry a strong inheritance of tho tendency to produce twins. In one herd of Swedish Red and While cattle it was found that a certain hull. Prins UeJonhjarla. sired 101 daughters of which 24 subsequently became mothers of twins, the percentage of twinning for these daughters being 9.17 per cent as in contrast to 2.7 1 per cent, for all other cows in tho herd, and 1.85 per cent as the average for the red and white breed.