AFP

IN THE world of poultry farming, the sexes are unequal. Broilers aside, hens can look forward, if that is the right phrase, to productive and reasonably long lives as layers of eggs for human consumption. Cocks are generally for the chop, a process that vexes animal-welfare activists. Only those few needed to keep the species going are allowed to live beyond chickdom.

Sorting the quick from the soon-to-be-dead, though, is a tedious process. “Vent sexing”, the most common way, requires a worker to squeeze a chick's anal vent, or cloaca, to clear the faeces and assess the size of a telltale bump inside the hole. Not the most popular of jobs. The alternative, “feather sexing,” is a form of cross-breeding that leaves females with detectably longer pin feathers than those of their male counterparts. This is slightly more salubrious, but the long-feather gene has been linked to other traits that may be undesirable to hatcheries, such as cancer. That discourages hatchers from adopting the method.

Yet chicken-sexing is a huge industry. The world's population of laying hens is now nearly six billion strong, according to the United Nations's Food and Agriculture Organisation. That is very nearly one hen for every human being. Time, then, to mechanise the process. And that is precisely what Tauseef Butt, a biomedical engineer and the boss of LifeSensors, of Malvern, Pennsylvania, proposes to do.

Dr Butt's new device is an oestrogen sniffer. It relies on the fact that female embryos produce this hormone in quantity and male ones do not. The sensor uses a fine needle to penetrate both the shell and the allantoic sac of an egg. This sac is a fluid-filled membrane that cushions the embryo and helps it trade carbon dioxide for oxygen from the air. (It is also the membrane that can make peeling a hard-boiled egg such a frustrating affair.)

The fluid sample thus extracted is mixed with genetically engineered yeast cells that fluoresce in the presence of oestrogen. The light so generated is recorded by a camera linked to a computer that keeps track of where the egg that produced the sample is now stored. Initial experiments, reported recently in the Journal of Animal Science, show that the process does not affect the hatchability of tested eggs, and appears to be virtually foolproof, if rather long-winded (the results are available only after two hours).

In future, Dr Butt envisages, the egg-sorting operation of a large hatchery might look like this: A conveyor belt moves the eggs along, gently jostling them until their allantoic sacs point upright. They then pass beneath an array of needles, which draw fluid from each. That done, they are sorted into bar-coded trays. Two hours later, once the samples have been analysed and the sex of each egg determined, they are returned to a sorter and divided by sex. The unfortunate male embryos then end up as pet food while the females go on to their lives as egg-mothers.

It would require some engineering (and a significant amount of storage space) to incorporate such a system into a hatchery. But the tweaks on the actual production line would be relatively minor, according to Dr Butt, and could be incorporated into the existing systems of robotic injectors used to pump vaccines into unhatched eggs.

Dr Butt reckons the cost of his system would be two or three cents per egg. The savings in labour, and in the cost of feeding and vaccinating cocks that slip through the existing procedures, should outweigh this. Sad for the redundant sexers, of course. But, as the adage has it, you can't make an omelette without breaking eggs.