Can cows discriminate people by their faces?

This experiment examines the cues used by cattle to discriminate between pe ople, particularly the role played by facial cues. We trained and tested ei ght Holstein cows 5 days each week for 2 months. For each cow, we used two people, a rewarder and a non-rewarder, of different size and dressed in ove ralls of the same colour. The operant chamber was a large box within which stood the two people. The cow could see, smell and touch each person. A lev er was placed in front of each person. When the cow pushed the lever in fro nt of the rewarder, it received 75 g of concentrate and nothing when it pus hed on the other one. For each test session, the cows made 10 choices. The placement of the people was determined randomly according to the Gellerman series. The success criterion was defined as at least eight correct choices out of 10 trials for two consecutive sessions (binomial law P<0.003). Duri ng the shaping, seven cows out of eight learned to press the lever to obtai n the food. The cows were then tested in a series of 10 trials with only th e rewarder present. Seven out of seven cows succeeded in reaching the succe ss criterion. In experiment 1, both the rewarder and the non-rewarder were present and standing upright at normal height and in full view of the cow. Five out of seven cows achieved the success criterion. In experiment 2, the cows could see only the faces of the two people. None of the cows were abl e to reach the success criterion. In experiment 3, both people were present standing up and wearing identical masks that completely covered their head s. Five cows out of five achieved the success criterion. In experiment 4, w e changed the relative height of the people. Five cows out of five succeede d when the two people stood so they were of equal height but with their fac es visible. However, no cows succeeded when the people were both of equal h eight and had their faces covered. This study suggests that cows seem to us e multiple cues to discriminate between people. Cows appear able to use eit her body height or the face to discriminate between people but use of the f ace alone is more difficult when the cows cannot see the rest of the body. (C) 2001 Elsevier Science B.V. All rights reserved.