Preliminary Observations on Avian Hysteria

Abstract

During the last two years a flock condition of hyperexcitability has been observed in laying hens and replacement pullets. It has been called avian to differentiate it from flightiness normally observed in White Leghorns. The first cases were observed in the summer of 1959. The cases reported increased in frequency in the late spring and summer of 1960. Historically, cases were reported as having occurred in 1958; and from descriptions, current cases of hysteria may be identical with a condition referred to as snake in the house and thought to be caused by snakes or predatory animals invading the house. Hysteria is usually of sudden onset, although a period of increasing nervousness has been reported. Affected chickens utter frightened cries and run at random, seeking shelter. In large pens this results in milling. Individual chickens seldom move very far, so that a wave of excitation moves the house. Before subsiding, the wave of excitation often runs the length of the building and returns to reafflict the original birds, which in the meantime have become quiet. In hysteria the excitation travels slowly from bird to bird compared with simultaneous takeoff of a pen of flighty pullets. The presence of a man in the pen has no effect on the milling. Each episode of excitation usually begins spontaneously within the flock; however, loud noise or rapid motion may initiate it. The period between episodes may vary from 2 minutes to many hours; the duration of each may be from 10 to 40 seconds. Mortality is primarily the result of piling, and occasionally from tears inflicted by claws. Even though injuries are severe, cannibalism is not a problem. Feather eating and lack of feathers appear to accompany hysteria, and feathers regrow on recovery. Recovery occurs in most cases within 6 weeks, and the diversity of the treatments that are followed by recovery complicates the search for a cause. Prolonged symptoms, lasting six months, have occurred in at least one case. Hysteria has been observed in all the major strains of Leghorns and in meat-strain replacement pullets. The ages at onset in 10 cases were: 14-18 weeks in 6 cases and 81/2-12 months in the other 4. In 19 additional cases, age at onset was 12-18 weeks in 15 cases and 71/2 months in the other 4. These cases plus 3 others (age not recorded) occurred on floor with litter. Whether the same thing occurs on wire is not definitely known, because the milling and hiding cannot be observed. There are reports of cases in which hysterical pullets did not quiet down when placed in cages. In hens a severe drop in production is observed, apparently because the hens are hiding and not eating. There is evidence that the condition is not contagious. In as many as half the cases reported in pullets, other chickens of the same age, older birds, and in some cases younger birds were housed on the same premises, often in adjacent pens, and failed to show evidence of hysteria prior or subsequent to the onset in the reported case. In two of the adult cases reported, the affected hens were placed in pens with normal hens without spread of hysteria to the normal hens. There are no gross lesions of