The whites of a cow's eyes could be a measure of its welfare.
Want to know how a cow is feeling? Look into its eyes. The more stressed a cow is, the bigger the whites of its eyes, say researchers in Norway1. Farmers and inspectors might use the difference as a measure of cattle welfare.
Agnethe Sandem and colleagues of the Agricultural University of Norway, Ås, gave one group of 12 Norwegian Red cows an open box of fresh grass and gave another 12 a similar box with a transparent perforated lid that stopped them eating the grass they could see and smell. The team video-d the animals' reactions.
The eye-whites of the frustrated group - even animals showing no other signs of stress - were over twice normal size. Stressed cows might open their eyes more to take in extra visual information that may help them deal with their situation, the researchers speculate.
Cows free to munch had whites less than half the size of cows not stimulated either way. Finding one indicator of animal welfare that might reveal well-being as well as stress is important, says Sandem: most are only negative.
"We are always interested in studies of animal welfare" says Timothy Brigstocke of the Royal Association of British Dairy Farmers, based in Leamington Spa, UK. Most dairy farmers make the wellbeing of their cows a priority, he says: "healthy cows are more profitable". But much bigger studies are needed, he warns, before such findings could be extrapolated to the whole dairy population.
At the moment, measurements of white blood cells, the hormone cortisol, heart rate and dehydration, are used to monitor stress, explains Carolyn Stull, who studies animal welfare at the University of California, Davis. But these tests are fiddly and slow.
A simpler measure may make it easier for those who work with cattle to monitor and change their practices, if necessary, says Sandem. She next plans to look at mother cows with and without their calves to investigate the wide-eye indicator further.
Sandem, A.I., Braastad, B.O. & Boe, K.E. Eye white may indicate emotional state on a frustration-contentedness axis in dairy cows. Applied Animal Behaviour Science, 79, 1 - 10, (2002).