Ventilation shutdown with heat and humidity may be superior to other methods of broiler depopulation under controlled environmental conditions, but this method requires further study under industry-like conditions, according to researchers at North Carolina State University.
The poultry industry has had much more experience depopulating turkeys and layers compared to broilers due to outbreaks of highly pathogenic avian influenza (HPAI). In 2015 and 2022, HPAI outbreaks caused massive losses to the poultry industry. Yet broilers made up only about 6% of the 96 million birds that died from the disease or were sacrificed.
In 2020, the COVID-19 outbreak resulted in the widespread shutdown of sit-down and fast-food restaurants. Because of reduced restaurant demand and labor shortages during the human COVID-19 pandemic, broiler producers had to depopulate large numbers of birds, approximately 2 million broilers. These depopulations mostly occurred in regions not usually impacted by HPAI.
Thus, the pandemic experience begs the question: When it comes to broilers specifically, how do approved methods of rapid depopulation compare?
The research team investigated three approved depopulation methods or modes of action — ventilation shutdown with heat, ventilation shutdown with heat and humidity and increased carbon dioxide atmosphere — to assess their effects on broiler stress parameters and behavior.
Current depopulation methods
They noted that current poultry depopulation methods approved by the American Veterinary Medical Association include water-based foam application, carbon dioxide atmosphere (by CO2 carts) and various forms of “ventilation shutdown plus” (VSD+). Foam application tends to be labor-intensive, and a large disease outbreak can cause shortages of depopulation supplies, including CO2.
“While ventilation shutdown plus heat (VSDH) and ventilation shutdown plus CO2 (VSDCO2) are approved,” the researchers stated, “there is still a need for quicker, less-stressful methods.”
A previous study with layers found that adding steam (heat plus high relative humidity) as a VSD+ method resulted in significantly faster first-hen mortality and complete mortality compared to VSDH alone. In any case, any use of VSD+ must be approved by the veterinary medical officers overseeing the depopulation.
Study design
In this study, the research team evaluated the addition of higher relative humidity (Rh) to VSDH, resulting in VSDHRh. They compared VSDHRh to VSDH and VSDCO2 for effectiveness in rapid, controlled-stress depopulation of broilers. Experimental data included time-of-death, stress parameters (electroencephalograms, blood chemistry, corticosterone, gene expression) and bird behavior.
“Adding relative humidity may result in a reduction in time to death,” they hypothesized.
The researchers conducted a two-phase experiment using randomly selected, mixed sex broilers from the Poultry Teaching Unit of the Prestage Department of Poultry Science. The birds had been raised to 42 days under identical conventional broiler grow-out conditions.
To control experimental conditions, the researchers used 4.75 cubic-foot, partially insulated Plexiglass® chambers to add heat, humidity or CO2 for both phases of the experiment.
The VSDH treatment started at 85.24° F (29.58° C) and rose to 101.86° F (38.81° C) with 85.55% Rh. The VSDHRh treatment started at 86.00° F (30.00° C) and rose to 107.20° F (41.78° C) with 82.70% Rh. The VSDCO2 treatment started at 0.28% CO2 (not significantly different from other treatments) and rose to 16.85% CO2.
The first phase analyzed the effects of the depopulation method on stress parameters and the concentration of Hsp70 (heat shock protein 70, a “molecular chaperone” expressed in response to stress) at the time of death. The second phase examined the progression of the stress parameters over time for each method.
An interesting feature of this experiment was the use of individual electroencephalogram (EEG) monitors to measure each bird’s brain electrical output in millivolts. This technique allowed correlation of EEG with bird behavior per mode of action during the depopulation process, along with accurate determination of time of death.
Results
The researchers found the most rapid depopulation via VSDCO2 (20 minutes to 100% depopulation), followed by VSDHRh (60 minutes) and VSDH (64 minutes).
The results “appear to indicate similarity among these methods as effective broiler flock depopulation methods with respect to their effects on each parameter measured over time,” they noted.
At the lower or upper EEG ranges, the methods caused no significant differences between conscious and unconscious behaviors. “However, around the midway point of each treatment, there was a noticeable shift toward unconscious behaviors,” the researchers observed.
They concluded that VSDHRh “may be a viable alternative method” for broiler depopulation, given its similarity to VSDH. They also suggested that VSDHRh may cause less stress in broilers due to lower Hsp70 levels.
Nonetheless, they cautioned that “more research needs to be conducted to fully understand how this treatment works in a non-environmentally controlled setting.”
What does this study mean for producers?
- To depopulate a broiler house, VSDHRh — for example, using steam — may work better than VSDH alone.
- Heat with added humidity may help reduce stress on broilers during depopulation.
- Any VSD+ method must be approved by the veterinary medical officers overseeing the depopulation.
The full paper, titled “The comparative effects of ventilation shutdown with heat (VSDH), relative humidity (VSDHRh), or CO2 (VSDCO2) on broiler electroencephalogram (EEG), blood chemistry and gene expression,” can be found in Applied Poultry Research and online here.
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