1 NOISE EFFECTS ON BEHAVIOR, PHYSIOLOGY AND PERFORMANCE OF INTENSIVELY MANAGED LAMBS1

40 Merino precocious lambs were divided into 3 test groups and a control group of 10, which were housed in 12 m2 sound-proof rooms. The lambs in the test groups were exposed to recordings of high-speed motor vehicle traffic noise for 8 hours a day. The frequency range of the recordings was 100 to 6,300 Hz, while the loudness levels were different in the three experimental rooms: group A=95 dB, group B=85 dB, and group C=75 dB. During the same 8 hours the control group was exposed to a background noise of 42-44 dB. For the rest of the day, the ambient noise level in the animal building was 35-40 dB. Noise determined a significant increase in the walking time (P<0.01) and a reduction of plasma cortisol levels (P<0.01) in the samples taken on days 28 and 42 of the trial in groups A and B. The lambs in the test groups exhibited a slower growth rate (P<0.01) than the animals of the control group, whereas a deterioration of feed efficiency was observed only in group A (P<0.01). There were no differences in terms of cell-mediated immunity and blood metabolites. Results suggest that exposure to noise has a detrimental effect on some biological functions in lambs but it does not severely impair animal well-being, at least when there are no concomitant conditions of physical and social discomfort