Systematic evaluation of laying hen exposure to atmospheric ammonia
Maintaining low atmospheric ammonia (NH3) concentrations in laying hen housing is a well-known challenge and recently has become the center of legislation for animal housing. In the winter months, poultry farm managers have to balance indoor temperature and environment (including atmospheric ammonia (NH3) concentrations) by adjusting the ventilation rates. To maintain the birds' thermal comfort, sometimes the ventilation rates are reduced, resulting in NH3 concentrations above the recommended concentrations. The United Egg Producers recommends atmospheric NH3 concentrations from below 10 ppm to a maximum of 25 ppm. Similarly, NIOSH recommends a time-averaged exposure limit of 25 ppm NH3 over an 8-h period for human safety. During extreme weather conditions, the NH3 concentrations in laying hen houses have been measured above these limits. A multi-disciplinary approach is needed to better understand the effects of NH3 exposure on laying hen health, production, behavior, and overall welfare. To better understand how NH3 affects laying hens, three studies were completed: long-term moderate concentration exposure, short-term high-concentration exposure, and preference/aversion behavior testing. The two exposure studies used a combination of measures, including pathology, immunology, and production. The preference testing was conducted in an environmental preference chamber that allowed the hens to move freely between four distinctly different ammoniated environments. The preference testing used measures of behavior, duration of occupancy, and the number of entrances to determine if hens displayed an aversion to the atmospheric ammonia. Finally, the data from all three of the studies was combined into a collective data set to apply a systems approach to evaluate for overall effects of NH3 concentration and duration. Long-term exposure was tested by housing the hens in either moderate NH3 (30 ppm) or fresh air (<5 ppm) for 25-50 wks. In the long-term exposure study, intra- & subepithelial heterophilic infiltrates were increased in the ocular conjunctival (P=0.0005) and heterophilic infiltrates of the lungs (P=0.0371). After 25 wks of exposure, there was an increased blood heterophilic/lymphocyte ratio (P=0.001) in the exposed birds; this increase was not significant at 45 wks of exposure. After 45 wks of exposure, some of the immunologic measures were increased, but they were not statistically significant. The short-term (two wks) high-concentration exposure test was designed to test the effects of those most extreme conditions (40-120 ppm) that have been measured during the winter months. In the short-term study, the 80 ppm treatment group had higher corticosterone concentrations (0 vs. 80 P=0.0087; 40 vs. 80 P=0.0147). They also had intra- and subepithelial heterophilic infiltrates in the ocular conjunctiva (P < 0.0001) and elevated lymphoplasmacytic infiltrates in the air sac (P = 0.033). The 34 wks old birds gained weight in all the treatment groups except for the 120 ppm treatment group in which they lost weight (P<0.0001). The 120 ppm treatment group also resulted in a lower feed disappearance ratio compared to 0 (P=0.0471) and 80 ppm (P=0.0103). Exposure tests help to elucidate the pathophysiology of the high NH3 exposure but don’t explain how birds perceive air quality. To assess this aspect of bird welfare, preference tests with NH3 concentrations of 0, 28, 57, and 114 ppm were used to assess occupancy, behavior, and postures. The birds showed no aversion to 28-114 ppm NH3 based on the total occupancy (P=0.211-0.3834), average duration (P=0.6575), or behavior (P=0.1446-0.9778). There was, however, a decrease in the average number of entrances (P=0.0004) for hens that had previously been exposed to 30 ppm NH3 compared to hens with no previous NH3 exposure. There have been inconsistent results reported in the literature regarding laying hens’ preference to different NH3 concentrations. Some studies have shown that birds have no aversion to NH3 less than 40 ppm, and one study found they have an aversion to NH3 over 25 ppm. The results of this study do not support the latter. A systems approach was applied to the collective data set to evaluate the effects of the different NH3 concentrations and exposure durations. This analysis was looking for both trends and commonalities between experiments, as well as gaps in information for future research. Based on this assessment, (a) NH3 concentration alone did not fully explain the observed differences; and (b) duration of exposure was important in determining the impact on laying hens. Ammonia exposure also acted as a depressant or stimulant, depending on the duration of exposure and concentration.
Poultry, Laying Hen, Ammonia, Aversion, Preference Testing, Livestock Housing, Air quality, Systems Thinking, Animal Welfare
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign