Effects of ventilation regimen on the welfare and performance of lactating ewes in summer.

A 6-wk trial was performed with thirty-six lactating Comisana ewes during the summer of 2001. The animals were divided into three groups of 12, which were designated low (LVR), moderate (MVR), and programmed (PROGR) ventilation regimens. In LVR and MVR rooms, fans provided 10 ventilation cycles of 12.5 and 25 min/h, respectively, whereas in the PROGR room, the fan was programmed to operate at 30 degrees C air temperature and 70% relative humidity. Mean ventilation rates were 33, 66, and 173 m3/h per ewe in LVR, MVR, and PROGR rooms. Air concentrations of microorganisms and dust and of gaseous pollutants were measured twice weekly. Respiration rate and rectal temperature were monitored throughout the trial at 1430. Behavioral traits of ewes were recorded once per week from 0930 to 1230. Cell-mediated immune response to phytohemagglutinin at d 3, 20, and 40 and humoral response to chicken egg albumin at d 11, 21, 30, and 40 were determined. At d 37, ewes were injected with 2 IU porcine ACTH/kg body weight(0.75) 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 weekly for composition and renneting parameters and fortnightly for bacteriological characteristics. Averages of temperature-humidity index values were 78.9, 76.8, and 74.5 in LVR, MVR, and PROGR rooms, respectively. The LVR and MVR treatments resulted in higher NH3 and CO2 air concentrations than PROGR treatment (P < 0.05). The LVR and MVR ewes had higher rectal temperatures than PROGR ewes (P = 0.001). LVR animals also exhibited higher idling compared to PROGR (P < 0.01) and lower feeding times than MVR (P < 0.05) and PROGR animals (P < 0.01). Ewes under the LVR treatment displayed significant lower averages of antibody titers and higher plasma cortisol levels than PROGR (P < 0.01) and MVR ewes (P < 0.05) 60 min after ACTH injection. The LVR treatment resulted in lower yields of milk (P < 0.01) and reduced feed efficiency (P < 0.01) than PROGR treatment. Results suggest that a fan-ventilated system, providing ventilation cycles during the warmest hours of the day and the night at a mean ventilation rate of 66 m3/ewe per hour, may sustain the performance and welfare in lactating ewes raised in warm climates during summer. A ventilation regimen, programmed to operate over upper critical air temperature and relative humidity, may be economically unattractive under these conditions.