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AbstractThe effects of ventilation regimen on air quality, and on the welfare and production performance of thirty-six Comisana ewes were assessed in a 6-week trial conducted during the summer of 2002. Animals were divided into three groups of 12, and subjected to the following treatments: low ventilation regimen providing a mean ventilation rate (VR) of 35 m3/h per ewe, split in 30 min ventilation cycles at an air speed of 2 m/s (LOV-30); moderate ventilation regimen (VR = 70 m3/h per ewe) split in 30 min ventilation cycles at an air speed of 4 m/s (MOV-30); moderate ventilation regimen (VR = 70 m3/h per ewe) split in 60 min ventilation cycles at an air speed of 2 m/s (MOV-60). Air concentrations of microorganisms, dust, and gaseous pollutants were measured twice weekly. Respiration rate (RR) and rectal temperature (RT) were monitored throughout the trial at 0830 and at 1400. Behavioral traits of ewes were recorded twice per week from 0900 to 1200 and from 1500 to 1800. Cell-mediated immune response to phytohemagglutinin (PHA) and humoral immune response to chicken egg albumin were determined. At d 37 ewes were injected with porcine ACTH, and subjected to blood sampling for evaluation of cortisol concentrations immediately before and 1, 2 and 4 h after ACTH injection. Milk yield was recorded daily. Individual milk samples were analyzed for composition, renneting parameters, somatic cell count (SCC), and bacteriological characteristics. Averages of maximum THI were about 3 points higher in the LOV-30 and the MOV-30 than in the MOV-60 room, whereas no differences emerged in the air concentrations of dust, gaseous pollutants and microorganisms. Significant interactions of treatment x time (P < 0.05) were found for respiration rate, and for the time the ewes spent lying, idling and eating in the afternoon during weeks 2 and 3 of the study period. Significant effects of ventilation regimen x time (P < 0.05) were also observed for milk yield and milk renneting parameters, the LOV-30 ewes giving smaller volumes of milk with a deteriorated coagulating behavior than those of the MOV-60 group during the second half of the trial. No significant differences emerged in ewe immune and endocrine responses. Results show that ventilation regimen had a moderate impact on ewe behavior, physiology and production performance. This experiment suggests that the length of ventilation cycles and air speed, together with ventilation rate, are critical for efficient ventilation regimens.