Mammals produce on average the same number of female offspring as they produce male offspring. From a gambling perspective, the chances are fifty-fifty.
Veterinarian Dorothea Friz realized that many farmers in Italy do not like those odds though. During her research there she found a male buffalo calf, disposed of in a trash bin.
Friz started researching further and posted her findings on the internet. "I found out that according to statistics only female buffalo calves are born in Italy's region of Campania," Friz said. "That's obviously impossible when it comes to the laws of nature."
Female buffalos are more desirable for farmers because their milk is used by farmers to produce mozzarella cheese. Friz figured male calves - that naturally cannot provide milk - are being killed right after birth in favor of female calves.
Females with the advantage
Cattle breeding expert Karl Schellander, from the Institute for Animal Sciences at the University of Bonn, says that male calves in Germany are not always doomed to die right after birth. However, young cattle of both sexes often don't have a very long life span.
"They often are fattened up and will be slaughtered after three, six or twelve months," Schellander told DW. "Then they will produce veal."
Female dairy cows are bred to provide a high amount of milk, up to 8,500 kilos per year. But dairy breeds, male as well as female, put on less meat than other cattle varieties. That's why it's not worth it for farmers to fatten the male calves for longer than one year.
Sperm to order
But, these days, if a dairy farmer wants a certain gender amongst his cows, he can get it. It's now possible to order so-called 'sexed sperm' from a fertilization facility, consisting of genetic material that will generally result in a particular gender of offspring, either male or female.
Sperm from a breeding bull is sorted by machines into samples containing only Y chromosomes and that containing only X chromosomes. Sperm that carries the X chromosome will result in a female calf after insemination, while the sample with Y chromosomes will create a male.
"The best machines can sort about 8,000 samples in one second, it works really quickly," Schellander said. "That's almost 15 million spermatozoa per hour."
On the open market one batch of gender-selected sperm costs about 40 euros ($53) - more than twice the amount of normal sperm. Its potency is also lower, which means a lower chance of pregnancy via artificial insemination.
"That's due to the fact that the sperm has to be treated, it has to flow through the machine," Schellander explained. "That means stress for the sperm."
But, even with modern technology, there are no guarantees that the gender of the newborn will really turn out the way the consumer wants. On average, one in ten calves is born with a different gender than what was hoped for.
At the moment, gender-selected sperm is only used in about five percent of cow births, according to Schellander. But, as male dairy calves are worth less than their female counterparts, this type of sperm sorting is sure to remain an option for some. So far, sorted sperm has only really been used by industrial cattle breeders.