Experiments made at the Royal Friedrich Wilhelm Stud-Farm gave the following results: In the case of 20 mares, which if Thury’s theory had been correct should all have given birth to fillies, 11 only fulfilled this expectation; but 10, on the other hand, were colts. Touchon, in his experiments at Hohenhau, obtained 11 calves and 2 foals, exhibiting the sex expected in accordance with Thury’s theory.
Düsing made a compilation of the figures given in all the experiments made to test Thury’s theory, with the following results: Cows fertilized early were delivered of 13 bull-calves and 29 heifers; mares fertilized early were delivered of 10 colts and 13 fillies; cows fertilized late were delivered of 5 bull-calves and 2 heifers.
Gerbe made experiments on rabbits, putting the buck to some doe-rabbits soon after the beginning of their heat, but to others as late as possible in their heat. On examining the young in the horns of the uterus, from the ovary downward, the distribution of the sexes was found to be approximately equal.
Whilst Coste’s experiments on a hen gave results contradictory to Thury’s theory, Albini’s experiments, made also on the common fowl, gave results in agreement with that theory. He found that the hens began again to lay fertilized eggs 3 to 6 days after intercourse with the cock (from which they had previously been kept separate); on the average, the distribution of the sexes in the chickens hatched from these eggs was approximately equal, with, however, a slight preponderance of cock birds. On the ninth and tenth days after separation from the cock the eggs laid were half fertilized and half unfertilized; on the twelfth day after separation from the cock the unfertilized eggs were in a great majority; but even as late as the eighteenth day after separation some of the eggs laid were still fertilized. The fertilized eggs laid from the tenth to the fifteenth day after separation when incubated produced a great preponderance of hen birds.
We have to thank breeders for a large number of experiments, such as those made by the breeder Fiquet, at Houston in Texas, who found that a bull upon whose sexual capacities excessive demands were made, procreated bull-calves exclusively; whereas in herds containing numerous bulls there were found among the calves born a preponderance of heifers. In thirty experiments on cattle Fiquet always found that the larger the number of cows a bull had to serve, and the longer they were kept in service, the larger was the proportion of bull-calves among their offspring. On the other hand, if certain cows had their sexual desires first satisfied by a gelded animal and were then served by a vigorous and lusty bull, an excessive proportion of heifers was born to these animals.
Janke obtained similar results in the breeding of sheep. In a report made to Düsing he states that in the early part of the lambing season more ewe-lambs are born than rams; in the latter part of the lambing season, on the contrary, more rams than ewes. The explanation he gives is that at the commencement of the pairing the rams are fresh and lusty, whilst later their potency is comparatively exhausted. In stud-farms, according to the same observer, it is a familiar experience that the most vigorous stallions serving a mare in the morning commonly procreate a filly; but if later in the day they serve a second mare they almost always procreate a colt. This, he thinks, finds its explanation in the fact that the stallion, when he serves the second mare, is in a condition of comparative sexual exhaustion, the more so because he usually covers the first mare twice.
Maritegoute’s breeding experiments at the sheep-farm of Blanc (Haut-Garonne), on the other hand, gave divergent results. In the early part of the pairing season, as long as the ram’s sexual powers were completely unimpaired, he procreated more male than female lambs. But when a few days later a great number of the ewes were simultaneously on heat and the ram, owing to very frequent acts of intercourse, began to be sexually exhausted, the procreation of female lambs was in excess. But when, finally, this period of maximum demands upon the ram’s powers was past, and the number of ewes on heat became once more small, the procreation of male lambs in preference to female was again observed.
The data obtained by Düsing from the Prussian stud-farms, in which, when greater sexual demands were made on the stallions, more males were procreated, have been already mentioned.
Fiquet made interesting experiments on cows and believed that in this way he was able to demonstrate the influence of nutrition upon the determination of sex—to such a degree, indeed, that he believed it was possible to breed calves of either sex at will. The following method gave him positive results in more than thirty instances. He never had the cow served by the bull at the first heat, but only at the second (if a cow is left unserved when on heat, the heat recurs after an interval of three weeks). The interval of three weeks was utilized in the preparation of cow and bull for the copulatory act. If a bull-calf was wanted the cow was supplied with the most invigorating fodder and was kept on the richest pasture available. The bull, on the other hand, that was to serve this cow was turned out to graze on the poorest pasture and was given poor fodder. At the end of the three weeks, when the cow came on heat for the second time, its sexual appetite was as intense as possible, whereas the bull showed but slight inclination to the sexual act. If the bull now served the cow a bull-calf was procreated. The opposite procedure led to the procreation of a heifer. For this purpose Fiquet kept the cow on low diet during the interval between the first and second heats, and had her first served by a castrated animal. When in this way, and by the low diet, the sexual appetite of the cow had been sufficiently diminished, it was served by a lusty bull, which for a long time had not been put to any cow, and the sexual potency of which had been increased to the uttermost by feeding it for several weeks on the most invigorating fodder.
The results of these experiments, according to which the nutrition of the parent-animals before the copulatory act has an influence upon the determination of sex, is explained by Düsing in this way, that nutrition influences also the quality of the reproductive products. “Poor nutrition gives rise to diminished functional capacity of the genital apparatus. Thus, for example, the production of semen is lessened. It can, in fact, hardly be replaced as quickly as it is used up. This occurs when there is a lack of adequate means of subsistence, and also when there is a lack of comparatively young males. In both cases alike we trace the effects in the birth of an excess of males. Converse conditions give rise to an excess of female offspring.”