Effect of Blood
Observations by the author during new restraint equipment start—ups in many plants indicate that blood from relatively calm cattle does not appear to frighten the next animal that enters a restrainer. The animal usually voluntarily enters a restrainer that is covered with blood. Some cattle may lick the blood. Blood or saliva from a highly stressed animal, however, appears to upset other cattle. If an animal becomes frenzied for several minutes, the cattle next in line often balk and refuse to enter the restrainer. After the equipment is washed, however, the cattle will enter. in one plant, a steer refused to walk over the spot where he had flipped over backward, and then refused to walk over dribbles of saliva that were smeared on the floor where he had flipped over. He voluntarily reentered the chute three times, but when he reached his saliva on the floor, he backed up through the chute for over 15 m. There is some evidence that there may be a "smell—of-fear" substance. In one study,36,37 blood from stressed rats was avoided by other rats, but human or guinea pig blood had no effect. According to animal behaviorist, Eible-Eihesfeldt, if a rat is killed instantly by a trap, the trap can be used again, but if the trap fails to kill instantly, it will be avoided by the other rats. 38
Possibly, the substance that the cattle are smelling is cortisol or some other substance that is secreted in conjunction with cortisol. Cortisol is present in the blood and saliva of cattle.39 Cortisol is a time-dependent measure, up to 20 minutes is required to reach peak values.40 The time course of cortisol secretion fits the author’s observations. If an animal is stressed for only a few seconds by an electric prod, the next animal usually remains calm and walks into the restrainer. The most serious balking and refusals to enter occur after an animal has become seriously stressed by becoming jammed in a piece of equipment. The other cattle often balk and refuse to enter for several hours.