HENS lay larger eggs if they smell a substance found in human urine, say
researchers in Britain and Israel. Oddly enough, the same substance also appears
to improve chickens鈥� memory.
Called 2-methoxy-3-isobutylpyrazine, the substance is one of five pyrazines
found in human urine. Abundant in nature, the pyrazine also turns up in the
scent glands of beavers, coyote urine and rabbit faeces. It is also used as a
flavour enhancer in processed food.
The egg-enlarging discovery came from a 4-month experiment in which cotton
wool dabbed with pyrazine was suspended outside the cages of 10 Leghorn
chickens. On average, the eggs laid by these hens weighed 4 grams more than
those laid by 10 Leghorns not exposed to the pyrazine鈥攇ains were between 5
and 10 per cent.
Advertisement
In total, the 800 eggs from the exposed birds weighed an extra 3.5 kilograms
compared with the 800 from the non-sniffers, says Miriam Rothschild, a British
researcher, now retired, who participated in the project with Anat Barnea of the
Open University of Israel.
鈥淲e don鈥檛 know how it happened,鈥� says Rothschild, who presented her findings
last week at New Frontiers in Science, an exhibition at the Royal Society in
London. One possibility, she says, is that the smell of pyrazine delays the
surge of luteinising hormone, which releases eggs from the oviduct, so a
developing egg might linger there. 鈥淚t might have more time to collect yolk and
albumen,鈥� she says.
Rothschild says that odours are known to influence the reproduction of many
small animals, such as rodents. But this is the first evidence that smell has an
impact on reproduction in birds. The team also found that when they were no
longer exposed to pyrazine, the chickens that had laid the larger eggs went back
to laying ordinary sized eggs.
In an accompanying experiment on 500 chicks, Rothschild and Barnea exposed
some birds to whiffs of pyrazine whenever they sipped water which had been laced
with quinine鈥攖o make it taste bitter and unpleasant. They found that birds
who received the smell cue were more likely to avoid drinking the bitter water.
鈥淚t appears they remember a disagreeable experience better if they are exposed
to pyrazine,鈥� says Rothschild.
She believes that the odour of pyrazine might have an attention-grabbing
effect on the sniffer, stimulating recall. The odour also occurs in many
brightly coloured but poisonous insects, such as tiger moths and ladybirds, and
might serve as a warning to predators.
In edible plants such as potatoes, red peppers and peas, lower levels of
pyrazine appear to have the opposite effect, stimulating appetite. But
Rothschild admits that this fails to explain how a whiff of pyrazine persuades
chickens to lay larger eggs.