Can steam be usable as a “plus” for ventilation shutdown?

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Source: Science Direct

SUMMARY

The American Veterinary Medical Association (AVMA), preferred depopulation methods (i.e., foam, containerized gassing, and mechanical methods) can be challenging when depopulating cage and aviary commercial laying hen houses for multiple reasons. When preferred methods are not feasible or resources are unavailable, ventilation shutdown plus (VSD+) heat and/or carbon dioxide (CO2) is approved for emergency situations. Both recognized “pluses” work but can have issues as VSD+ heat typically causes a decrease in environmental humidity and can affect PVC structures, while CO2 can be a human safety concern and has procurement problem during emergencies. Steam supplies both heat and humidity, the latter hindering birds’ ability to dissipate body heat through evaporative cooling, thus expediting hyperthermia. The objective of this study was to evaluate effectiveness of VSD+ with steam as a “plus” for depopulation of laying hens in a cage-free aviary system. Approximately 1,800 Lohmann Brown hens aged 56 wk were housed in Big Dutchman Natura 60 aviaries in 4 rooms. Four VSD+ treatments were as follows: 1) control or VSD+ heat (VSD-H), 2) VSD with steam (VSD-S), 3) VSD with heat and then steam to maintain temperature and humidity (VSD-HS), and 4) VSD with steam and then heat to maintain temperature (VSD-SH). All VSD+ procedures followed AVMA depopulation guidelines for temperature and time (i.e., 40°C within 30 min). Hens were monitored via cameras for times to first and 100% mortality. After depopulation was completed mortality location within each tier of system (floor area, first tier, second tier, and third tier) were recorded. Data were analyzed in SPSS v. 28 and significance was at P < 0.05. Observed time to first mortality for VSD-H, VSD-S, VSD-HS, and VSD-SH were 82.7-min, 56.6-min, 49.6-min, and 52-min. While 100% mortality for VSD-S was 112.3-min; VSD-HS was 83.3-min; VSD-SH was 103.6-min; and VSD-H never reached 100% mortality in time limit. Mortality location revealed VSD-S and VSD-SH had more carcasses located in floor area than VSD-HS (P = 0.02); VSD-S and VSD-SH had less carcasses than VSD-HS (P = 0.02) in first tier and third tier; no differences were observed between treatments in second tier (P = 0.248). Hens in steam treatments were faster in reaching time to first and 100% mortality than hens in VSD-H (P < 0.05). Results indicated that steam alone, or in combination with forced air heat, could be recognized and used as a “plus” for VSD+ depopulation of laying hens reared in a cage-free or aviary housing system.

DESCRIPTION OF PROBLEM

Over the last decade, several events in the United States of America (US) have led to emergency mass depopulation of domestic poultry. In 2015, the highly pathogenic avian influenza (HPAI) outbreak resulted in depopulation of 7.5 million turkeys and 42.1 million egg-layer and pullet type chickens (USDA-APHIS, 2016a). During the COVID-19 pandemic, some processing plants ceased operation due to disease outbreaks amongst workers, and premises cleaning and disinfection for workers to safely return (Marchant-Forde and Boyle, 2020). In addition, decreased demand during COVID-19 for poultry products from restaurants and foodservice businesses resulted in the need for less poultry to be processed (Sharma et al., 2020). Decreased demand and processing plant closures resulted in emergency depopulation of 2 million broilers and 61,000 laying hens (Kevany, 2020). Beginning in 2022, the United States experienced another extensive HPAI outbreak. A total of 58.79 million domesticated fowl have been depopulated (including both commercial and backyard flocks) (USDA-APHIS, 2022). According to the US Department of Agriculture, Economic Research Service (USDA-ERS), a total of 43.3 million table-egg layers were lost to HPAI in 2022 (USDA-ERS, 2023).

During the multiple HPAI outbreaks of 2015, the US government was overwhelmed with the ability to depopulate flocks in a timely manner utilizing “the approved methods of CO2 carts for layers or firefighting foam for turkeys” (Gingerich, 2015a). Upon reflection and to be better prepared if another severe HPAI outbreak occurred, USDA-APHIS established and announced its position on usage of VSD in 2015 (Gingerich, 2015a). This decision came from a 2009 precedent set by the United Kingdom’s Department for Environment, Food, and Rural Affairs (DEFRA), where VSD was recognized as a method to depopulate flocks and instructions for VSD were developed for use in such emergencies (DEFRA, 2009; Gingerich, 2015a). In 2019, the AVMA released a guideline for mass depopulation of animals to aid U.S government officials in determining which depopulation method to use during emergency circumstances. The approved depopulation methods outlined by AVMA fall under 2 categories, “preferred methods” and “permitted in constrained circumstances”, but ultimately USDA makes the final decision on what methods will be implemented in each emergency case (USDA-APHIS, 2017; AVMA, 2019). For poultry, methods are approved based on whether birds are indoors or outdoors and if birds are floor-reared or caged. For the present study, the focus will be on floor-reared confined poultry, as aviary style housing was included in this category (AVMA, 2019; Marchant-Forde and Boyle, 2020). Preferred depopulation methods for this category are water-based foam; whole house, partial house, or containerized gassing; cervical dislocation, mechanical assisted cervical dislocation; and captive bolt gun (AVMA, 2019; AAAP, 2021). Additionally, methods permitted in constrained circumstances are: VSD+, controlled demolition, exsanguination, and decapitation (AVMA, 2019; AAAP, 2021). When a farm has tested positive for HPAI, USDA Animal and Plant Health Inspection Service (APHIS) guidelines require depopulation to begin within 24-h (of confirmed diagnosis) to 48-h to “stamp out” virus and avoid “lengthier depopulation process that may lead to a greater number of birds suffering” (USDA-APHIS, 2016b). However, such time constraints may not allow adequate preparation time for implementation of AVMA’s preferred depopulation methods. In such cases when the preferred depopulation methods cannot be utilized, producers, alongside government response officials, must consider methods permitted under constrained circumstances, most notably ventilation shutdown plus heat and/or CO2 (VSD+).

VSD+ has been approved as a last resort method if preferred methods do not meet required USDA foreign animal disease response timing criteria due to a lack of available resources, worker safety or logistics (Gingerich, 2015b). VSD is defined as the “cessation of natural or mechanical ventilation of atmospheric air in a building where birds are housed, with or without action to increase ambient temperature, resulting in an increase of indoor temperature and eventual death of animals” (Gingerich, 2015b). However, VSD alone is not recommended and supplemental heat and/or carbon dioxide must be added, referred to as VSD+.

Eberle-Krish et al. (2018), investigated addition of CO2 to VSD+ to depopulate laying hens in a conventional-caged structure. One hundred percent mortality was achieved within 90-min by addition of CO2 and within 120-min with supplemental heat. However, VSD alone was unable to reach 100% mortality after 225-min of implementation. Zhao et al. (2019) modeled the indoor environment and supplemental heat requirement for VSD+. Modeling and experimental results indicated that hyperthermia was leading cause of death during VSD+ and noted that having a high relative humidity would help hasten depopulation procedures (Zhao et al., 2019).

A major limitation to CO2 usage is associated cost and possible supply shortage. As a result of the COVID-19 pandemic and unexpected events, the U.S government declared a national CO2 shortage during 2022 (Greenwood, 2020; Chappell, 2022; Clouse, 2022; Taylor, 2022). CO2 supply shortage can be attributed to contamination in the largest natural CO2 production hub, planned/ unplanned ammonia plant closures for maintenance, decreased fuel demand and production during COVID-19 pandemic, and labor shortages in transportation (Greenwood, 2020; Chappell, 2022; Clouse, 2022; Taylor, 2022). When evaluating CO2 properties, CO2 is denser than air, so theoretically, a higher concentration would be found in the floor area of an aviary system compared to the remainder of system. Stratification of CO2 becomes problematic in these systems because chickens can detect CO2 concentrations at very low levels (5.0%–7.5%) and will actively choose to avoid inhaling air with 60% CO2, meaning birds might move from floor area to higher tiers of aviary (Raj and Gregory, 1991; Sandilands et al., 2011).

After death, removal of carcasses from these systems could be challenging due to rigor mortis, especially leg and foot muscles that contract and “grasp” metal wire flooring in aviary housing systems (Duncan, 2001). Elevated environmental temperatures may also influence onset of rigor mortis. Carcasses of animals that have died in a hotter environment, such as the temperatures observed in VSD+, would encounter accelerated chemical changes leading to autolysis as opposed to in a colder environment (Mesri et al., 2017).

Birds are homeothermic animals and can maintain a core body temperature between 40°C and 42°C, when environmental temperature is within thermoneutral zone (18°C to 24°C) (Donald and Williams, 2001; Anderson and Carter, 2004; Daghir, 2008; Nawab et al., 2018; Lohmann, n.d.; University of Kentucky, n.d.). There are 2 anatomic features that can delay birds’ ability to effectively dissipate heat: feathers and absence of sweat glands. Feathers function as a form of insulation, trapping warm air close to the body, which inhibits heat loss (Donald and Williams, 2001; Anderson and Carter, 2004). Birds can use head appendages (e.g., comb) and unfeathered area under wings (i.e., apteria) to aid in direct heat loss; however, chickens use a process of respiratory evaporative cooling to compensate for absence of sweat glands (Donald and Williams, 2001; Gerken et al., 2006; Daghir, 2008). Respiratory evaporative cooling occurs when moisture evaporates from the damp lining of the respiratory tract (Donald and Williams, 2001; Lohmann, n.d.; University of Kentucky, n.d.). Birds will increase their respiration rate through 2 stages of thermal panting (referred to as thermal tachypnea or thermal polypnea) to increase respiratory evaporative cooling and reduce core body temperature (Dawson, 2000). Using thermal panting to reduce core body temperature can be a vigorous activity, especially at higher humidities, for this reason many birds supplement thermal panting with rapid fluttering of the gular area (gular flutter) (Dawson, 2000). Although respiratory evaporative cooling can be extremely effective in maintaining core body temperature, there are consequences if birds pant for a prolonged period, primarily increased loss of dissolved carbon dioxide in blood. Excessive loss of carbon dioxide results in an increased blood pH, causing respiratory alkalosis and eventual death if not resolved (Donald and Williams, 2001; Anderson and Carter, 2004; Robertshaw, 2006).

Both elevated temperature and relative humidity can have detrimental effects on birds’ health if not managed properly (Donald and Williams, 2001; Daghir, 2008). For example, if ambient temperature reaches approximately 29.4°C, but relative humidity stays low (∼50%), birds are still able to effectively dissipate heat through respiratory evaporative cooling (Nawab et al., 2018; Lohmann, n.d.). However, when relative humidity increases above 70%, the amount of moisture that can be evaporated from birds’ respiratory tract decreases and therefore amount of heat that can be removed through thermal panting or gular flutter decreases (Lohmann, n.d.). During the study performed by Eberle-Krish et al. (2018), the observed relative humidity during VSD+ procedures were between 74% and 92% for VSD; within 73% and 84% for VSD with supplemental heat; and 80% to 88.9% for VSD with addition of CO2. A plausible reason as to why relative humidity was high during this study is related to how the experimental room was designed. Authors described the cages as completely enclosed from both sides, creating a chamber; the chamber was then sealed with a 10-mil polyethylene plastic ceiling (Eberle-Krish et al., 2018). Since ventilation of room was turned off, and chambers were sealed and tightly enclosed, moisture loss through hen’s evaporative cooling was trapped, thus leading to a higher humidity that cannot escape. Room setup may not accurately depict relative humidity of a large commercial facility.

While forced air heaters increase temperature, air is passed through a flame or heating element and relative humidity is decreased based on moisture holding capacity of warm air. Utilization of steam as a “plus”, should simultaneously increase temperature and relative humidity of birds’ environment, consequently hindering ability to effectively dissipate heat, thus leading to a quicker depopulation process. Although steam as a “plus” has not been explored in poultry, VSD+ steam was investigated for swine depopulation. During the COVID-19 pandemic Baysinger et al. (2021) explored alternatives to depopulate swine in US Midwest region, particularly through use of VSD+ supplemental heat and steam. VSD+ steam surpassed AVMA recommendations with a 95% mortality rate in <1 h and overall survival rate of 0.3%. Therefore, the objective of the current study was to evaluate the effectiveness of VSD+ with steam as a “plus” for depopulation of laying hens in a cage-free system. The hypothesis was that supplementation of steam would increase both temperature and relative humidity of the laying hen room during VSD+ and expedite time to death through hyperthermia.

MATERIALS AND METHODS

Research was conducted at Michigan State University Poultry Teaching and Research Center (East Lansing, MI). All procedures involving live birds were approved by Michigan State University Institutional Animal Care and Use Committee (IACUC-202100026).

Housing and Birds

For this study, approximately 1,800 Lohmann Brown hens (Hy-line North America, LLC, GA) aged 56 wk were housed at Michigan State University Poultry Teaching and Research Center. Hens were kept in 4 identical rooms measuring 19.81m × 4.57m × 3.20m (length × width × height) that were equipped with Big Dutchman Natura 60 Aviaries (NATURA60, Big Dutchman Inc., Holland, MI). Each room had approximately 450 hens and rooms were further divided into 3 identical sections (150 hens/section; 0.093 m2/bird) of the multitier aviary system to approximate industry stocking density (United Egg Producers, 2017). Each aviary section had identical equipment arrangement (i.e., 3 tiers, open floor area, water lines, feeders, nest boxes). The first tier included a single internal water line, external feeder line, outer and inner perches, and opening to floor area; second tier had an internal feeder line, and outer perch; and third tier included single internal water line, nest boxes, and inner and outer perches. Hens were able to freely move within their respective sections but could not access other sections of aviary since sections were internally divided by a wire mesh.

Experimental Room Design

The multitier aviary was located in the center of each room, with each aviary section facing the wall (Figure 1). On one side, there was a worker isle that was used for egg collection (referred to as man side), while the other side was the sections of the aviary (referred to as bird side). The front end of the room contained 2 air inlets and entrance to room (referred to as controller side), and the back end contained 2 exhaust fans (referred to as exhaust fan side). A 76.2-cm 9000 CFM pedestal fan was positioned within rooms to mitigate heat stratification (HVP-30-MF, Menards, Inc., Eau Claire, Wisconsin). Immediately prior to VSD+, the drinking water system was turned off. Although nest boxes were closed before VSD+ treatments were applied, hens still had access to third tier. There was one room (VSD-HS treatment) where nest boxes could not be closed due to equipment malfunction.

Figure 1

Figure 1. Aerial view of room layout. Aerial view of treatment room layout. Room layout and measurements were identical between treatments (19.81 × 4.57 × 3.20 m [length × width × height]), with the exception for VSD-H treatment since no steam was supplemented. Aviary system consisted of 4 sections, each with their own floor area; however, only 3 sections were used to house hens in present study. Diagram not drawn to scale.

VSD+ Treatments

Due to daily boiler, room setup and takedown, treatments were conducted over the span of 4 d (1 room/d) and each room was randomly assigned to a VSD+ treatment (1 treatment/d). Temperature and relative humidity outside of the facility (where the boiler was located) were monitored by World Weather Forecast Service (n.d.). In accordance with AVMA standards, the goal was to raise the temperature of rooms to 40°C (104°F), within 30-min, and maintain temperature between 40°C and 43.3°C (104°F to 110°F) for a minimum of 3-h (AVMA, 2019). These standards resemble the ones developed by DEFRA, but DEFRA goes a step further and states that, if possible, the relative humidity of the bird house/barn be maintained at 75% or higher for the 3-h minimum (DEFRA, 2009). All data collection had a 3-h limit due to MSU IACUC protocol. Hens that remained alive past 3-h limit were humanely euthanized, either through cervical dislocation or use of CO2 depopulation cart according to farm protocols. Considering that steam boiler usage did not allow for relative humidity to be manipulated to a specified percentage, 2 combination treatments (VSD-HS and VSD-SH) were created.

Treatment 1: VSD With Supplemental Heat (VSD-H). In this treatment, the room ventilation system was shut off, air inlets were sealed via wood panels and door was sealed by a fire-retardant plywood sheath (1235400, Menards, Inc., Eau Claire, WI). Only supplemental heat was added to the room via forced air heaters. The salamander forced air heater was used to heat room to 40°C, then the wall mounted forced air heater was used to maintain temperature.

Treatment 2: VSD With Steam (VSD-S). In Treatment 2, the ventilation system was shut off and the room was sealed in same manner as Treatment 1, but the door of the room was closed off (as opposed to usage of fire-retardant plywood sheath in Treatment 1). Only supplemental steam was introduced into room through low pressure steam boiler.

Treatment 3: VSD With Supplemental Heat and Steam (VSD-HS). In Treatment 3, the ventilation system was shut off and room was sealed in same manner as Treatment 1. Supplemental heat and steam were added to the room. First, the salamander forced air heater heated room to 40°C. After 40°C was achieved, steam was administered to room. Treatment explored if steam could maintain the required temperature for 3-h.

Treatment 4: VSD With Supplemental Steam and Heat (VSD-SH). In Treatment 4, the room ventilation system was shut off and room was sealed in same manner as Treatment 2. Supplemental steam and heat were added to room. First, steam was administered to heat room to 40°C. After 40°C was achieved, steam pressure was reduced (not completely turned off) and the wall mounted forced air heater was used to maintain heat. This treatment investigated whether steam could reach the required temperature within 30-min.

Environmental and Animal Monitoring

Ambient temperature and relative humidity of rooms was recorded via USB data loggers (EL-USB-2, LASCAR Electronics, Erie, PA). Data loggers were placed on upper and lower positions of aviary system (first and third tiers), <1.22 m vertical distance from one another, and in front and back sections of aviary to collect environmental data (4 loggers/room). Data loggers were set to record temperature and relative humidity every 30-s. The controller system from each room was used to monitor temperature conditions in real time during VSD+ treatments (Command III, Poultry Management Systems, INC, Lowell, MI).

CCTV cameras were used to monitor each room and were 4k ultra-HD resolution dome cameras, and an NVR recording system was set up to record and discourage entry into rooms until all hens were observed to be deceased or the 3-h limit was reached (4 cameras/aviary section; total of 12 cameras/room) (LNE9292B, LOREX Corp., Linthicum, MD; N882A63B, LOREX Corp., Linthicum, MD). Each section had 2 cameras mounted on the bird side wall to record each tier of aviary, one camera mounted on the ceiling for an aerial view of floor area, and one on the man side of aviary to record floor underneath system and tier 1. This camera layout allowed for maximum viewing area within aviary system. Unconsciousness and death were determined by video observation of hens for signs of loss of posture, neuromuscular spasms, and cessation of movement (Webster and Fletcher, 2001; Eramus et al., 2010).

Since a large quantity of video footage was gathered, 4 observers were trained by an experienced researcher to identify when hens started recumbency (either lateral or sternal) and when all hens were recumbent (interobserver reliability ≥85% between observers). Then, based on analysis from observers, observed times to first and 100% mortality were confirmed by an experienced researcher. To determine the time to first and 100% mortality, an experienced researcher analyzed videos for first and last hen to be seen exhibiting behavioral indicators of death previously described (i.e., loss of posture, neuromuscular spasms, and cessation of movement) (Webster and Fletcher, 2001; Eramus et al., 2010).

Heaters and Boiler

A salamander-style forced air heater with a heating capacity of 400,000 BTU was utilized as the main source of heat for this experiment (Boss 400 DF, L.B. White Company, LLC, Onalaska, WI). The door to each room was sealed via fire-retardant plywood sheath, in VSD-H and VSD-HS treatments, a hole was made in shape of salamander style forced air heater that was located in the hallway outside of each room during the study. Unfaced fiberglass insulation was placed in empty spaces between plywood sheath and heater to minimize leaks (523897, Menards, Inc., Eau Claire, WI). A wall mounted forced air heater within MSU research facility was used as a secondary heat source, primarily to maintain required temperatures during VSD+ treatments, with minimum heating capacity of 50,000 BTU and maximum heating capacity of 100,000 BTU (Guardian Forced Air, L.B. White Company, LLC, Onalaska, WI).

A 30 hp low pressure steam boiler was rented to supply steam for the 3-h limit. A 5.08 cm hole the size of the steam pipe was made on one of the wood panels covering the air inlet to administer steam into the room. Since steam entered the room through an air inlet, it allowed the steam to stay at the ceiling level and away from the hens (i.e., hens were not in direct contact with the steam). The boiler was located outside of the entry doors of facility sealed rooms due to operating safety regulations. The boiler operated at 5 PSI during VSD+; as steam was not released under pressure, the pipe was open to the room without the need of diffuser or other equipment. A total of 113.4 kg of saturated steam was delivered per hour (1.9 kg/min).

Statistical Analysis

Data were analyzed using GLM procedure of SPSS 28 (IBM, Armonk, NY). Statistical significance was considered at P < 0.05. The study was a completely randomized design, and the experimental unit was an aviary section (N = 3 aviary sections/room). Data were analyzed for differences in time to first mortality and 100% mortality, mortality location, temperature, and relative humidity between treatments. Means were separated post hoc with Tukey’s Least Significant Difference Test.

RESULTS AND DISCUSSION

Observed Times for First and 100% Mortality

Mean length of time to achieve first and 100% mortality for all treatments are reported in Table 1. Observed time to first mortality was shorter (P < 0.0001) in all steam treatments compared to VSD-H treatment. VSD-S, VSD-HS, and VSD-SH were comparable between one another but quicker (P < 0.0001) in achieving 100% mortality than VSD-H. For this project, 100% mortality was unachievable for VSD-H within allotted 3-h limit (70% of hens survived).

Table 1. Mean length of time to first and 100% mortality for VSD+ treatments.

VSD+ treatment1 First mortality (min) 100% mortality (min)
VSD-H b82.7 ± 5.8 b180.0 ± 0
VSD-S a56.7 ± 0.7 a112.3 ± 13.4
VSD-HS a49.7 ± 0.3 a83.3 ± 5.0
VSD-SH a52.0 ± 1.0 a103.7 ± 6.17
P-value <0.0001 <0.0001

Mean times (minutes) to observed first and 100% mortality for each VSD+ treatment.

1

VSD-H= VSD+ heat only; VSD-S= VSD+ steam only; VSD-HS= VSD+ heat (for 30-min) and then steam; VSD-SH= VSD+ steam (for 30-min) and then heat.

a,b

Means ± SEM within a column having different superscripts differ significantly (P < 0.05).

Mortality Location Within the Aviary

Table 2 provides the location of mortality within aviary system upon completion of each VSD+ treatment. Within the floor area, fewer carcasses were observed in sections of room subjected to VSD-HS (P = 0.02) compared to VSD-S and VSD-SH, which had an overall higher number of carcasses. In tier 1, VSD-S and VSD-SH had a lower carcass amount, while VSD-HS had higher number of carcasses (P = 0.006). No differences were detected in tier 2 (P = 0.248). For tier 3, treatments that utilized steam first (VSD-S and VSD-SH) were comparable in carcass number but lower (P = 0.024) than VSD-HS. VSD-H results were removed from statistical analysis due to higher-than-expected survivability which might have skewed results. However, mortality location for VSD-H was expressed as an average percent and should not be used for comparison between steam treatments. To find the average percentage, first the number of carcasses in each location of the aviary was determined and the total sum for each section was determined. Then, the number of carcasses was divided by the total sum per section and multiplied by 100. Lastly, after a percentage of carcasses per location and per section were obtained, the average for the room was attained. A majority of the carcasses were located in the floor area (37.34%); 28.12% were located in tier 1; 18.04% were found in tier 2; and 1.04% was located in tier 3.

Table 2. Mortality location within the aviary.1

VSD+ treatment Floor Tier 1 Tier 2 Tier 3
VSD-S a111.3 ± 4.3 b18.7 ± 2.0 18.0 ± 2.6 b2.0 ± 0
VSD-HS b81.0 ± 5.0 a40.7 ± 0.3 17.0 ± 2.1 a11.3 ± 3.2
VSD-SH a115.3 ± 4.7 b22.7 ± 2.9 11.7 ± 1.8 b0.3 ± 0.3
VSD-H* 37.34%* 28.12%* 18.04%* 1.04%*
P-value 0.02 0.006 0.248 0.024

Mean number of mortalities in each tier of aviary system after 3-h time limit.

1

VSD-H= VSD+ heat only; VSD-S= VSD+ steam only; VSD-HS= VSD+ heat (for 30-min) and then steam; VSD-SH= VSD+ steam (for 30-min) and then heat.

Obtained average percentage for mortality location in VSD-H treatment not used for comparison in statistical analysis between steam treatments.

a,b

Means± SEM within a column having different superscripts differ significantly (P < 0.05).

When carcass location within the aviary system was evaluated after depopulation, VSD-S and VSD-SH had an overall greater number of carcasses in the floor area compared to other areas of the system. Based on these results, carcass removal after VSD+ with steam application may be less challenging for workers than other depopulation methods since the majority of carcasses would be located in floor area, outside of the system. The idea that carcass removal after VSD+ with steam may be less troublesome for workers compared to VSD+ CO2 might be true, as chickens can detect low concentrations of CO2, thus hens might move into the multi-tier aviary and out of floor area and eventually die inside aviary.

Room Temperature

When VSD+ treatments were conducted, average out-of-doors temperature for VSD-H, VSD-S, VSD-HS, and VSD-SH were 22.8°C, 27.2°C, 26.1°C, and 22.8°C, respectively (World Weather Forecast Service, n.d.). Table 3 exhibits the room temperature recorded during each VSD+ treatment. The AVMA-specified temperature of 40°C must be achieved within 30-min and all VSD+ treatments were able to reach temperature and no differences (P = 0.18) were detected between treatments at 30-min.

Table 3. Room temperature recorded for each VSD+ treatment.1

Empty Cell VSD+ treatments2 Empty Cell
Time (min) VSD-H VSD-S VSD-HS VSD-SH P-value
0 a20.1 ± 0.1 c23.5 ± 0 b22.3 ± 0.3 b22.5 ± 0 <0.001
5 a21.5 ± 0.3 c23.5 ± 0 bc22.6 ± 0.1 b22.5 ± 0 <0.001
10 a23.2 ± 0.2 a23.7 ± 0.2 a22.8 ± 0.1 a22.8 ± 0.3 0.042
15 a22.6 ± 0.1 b26.7 ± 0.9 b27.0 ± 1.1 b27.3 ± 1.3 0.009
20 a24.4 ± 0.4 b32.8 ± 1.2 b34.3 ± 2.0 b33.0 ± 1.5 0.002
25 a32.4 ± 1.0 a36.0 ± 1.0 a40.0 ± 2.5 a37.3 ± 1.3 0.06
30 39.3 ± 1.5 39.3 ± 0.9 44.9 ± 2.7 40.5 ± 1.0 0.181
35 44.8 ± 1.9 41.7 ± 0.7 47.1 ± 2.4 43.0 ± 1.0 0.301
40 45.8 ± 2.1 43.0 ± 0.8 46.3 ± 1.6 45.5 ± 1.0 0.586
45 43.8 ± 1.8 43.7 ± 0.7 46.8 ± 1.0 45.0 ± 0.5 0.325
50 47.9 ± 1.8 44.2 ± 0.4 48.4 ± 0.9* 43.8 ± 0.3* 0.076
55 ab48.0 ± 1.8 ab44.8 ± 0.3 b49.3 ± 0.8 a43.3 ± 0.3 0.041
60 ab47.1 ± 1.6 ab44.8 ± 0.3* b49.5 ± 0.6 a43.3 ± 0.3 0.018
65 ab46.8 ± 1.5 a44.3 ± 0.3 b49.1 ± 0.4 a43.3 ± 0.3 0.012
70 ab46.6 ± 1.4 ab44.0 ± 0.3 b48.1 ± 0.4 a43.5 ± 0.5 0.025
75 ab46.9 ± 1.2 a43.7 ± 0.2 b47.6 ± 0.4 ab44.0 ± 0.5 0.021
80 a46.9 ± 1.2 a43.5 ± 0.3 a47.0 ± 0.4 a44.3 ± 0.8 0.039
85 b47.1 ± 1.1* a43.2 ± 0.2 ab46.6 ± 0.4⁎⁎ ab44.5 ± 0.5 0.016
90 b47.4 ± 1.2 a43.2 ± 0.2 ab46.1 ± 0.4 ab44.8 ± 0.8 0.033
95 b47.6 ± 1.1 a43.2 ± 0.2 ab45.9 ± 0.2 ab45.3 ± 0.8 0.014
100 b47.8± 1.2 a43.7 ± 0.2 ab45.1 ± 0.4 ab45.5 ± 1.0 0.033
105 b46.4 ± 1.1 ab44.2 ± 0.2 a42.6 ± 0.5 ab45.3 ± 0.8⁎⁎ 0.03
110 b45.0 ± 0.9 b45.2 ± 0.2 a39.4 ± 0.7 b45.0 ± 0.5 <0.001
115 45.0 ± 0.7 45.7 ± 0.2⁎⁎ 44.8 ± 0.3 0.612
120 46.0 ± 0.8 46.2 ± 0.2 44.8 ± 0.3 0.402
125 46.6 ± 0.9 46.5 ± 0.3 44.8 ± 0.3 0.295
130 46.6 ± 0.9 46.8 ± 0.3 44.8 ± 0.3 0.254
135 45.6 ± 0.8 46.8 ± 0.3 44.8 ± 0.3 0.237
140 44.6 ± 0.8 46.7 ± 0.2 45.3 ± 0.3 0.144
145 44.0 ± 0.7 46.7 ± 0.2 45.3 ± 0.3 0.046
150 44.8 ± 0.6 46.7 ± 0.2 45.3 ± 0.3 0.07
155 45.6 ± 0.7 46.7 ± 0.2 45.3 ± 0.3 0.279
160 46.4 ± 0.8 46.8 ± 0.3 45.3 ± 0.3 0.376
165 47.3 ± 0.8 46.8 ± 0.3 45.3 ± 0.3 0.211
170 46.9 ± 0.9 47.0 ± 0.3 45.8 ± 0.3 0.547
175 45.8 ± 0.8 47.2 ± 0.2 45.8 ± 0.3 0.258
180 44.8 ± 0.8 47.2 ± 0.2 45.8 ± 0.3 0.07
1

Mean room temperatures (°C) during VSD+ treatments. Environmental parameters were measured every 30-s and means are based on average of 4 data loggers placed throughout each room.

2

VSD-H= VSD+ heat only; VSD-S= VSD+ steam only; VSD-HS= VSD+ heat (for 30-min) and then steam; VSD-SH= VSD+ steam (for 30-min) and then heat.

a,b

Means± SEM within a column having different superscripts differ significantly (P < 0.05).

Indicates at what time and temperature the first observed mortality occurred for each VSD+ treatment.

⁎⁎

Indicates at what time and temperature 100% observed mortality occurred for each VSD+ treatment (VSD-H never reached 100% mortality).

Ventilation Shutdown With Supplemental Heat (VSD-H). The VSD-H room temperature prior to treatment was 20.1°C and reached a room temperature of 39.3°C within 30-min after the treatment began (Table 3). A maximum temperature of 48.0°C was obtained at approximately 55-min while during the last half of treatment, the room temperature fluctuated between 44.0°C and 46.0°C. At 85-min, the first mortality was observed at a room temperature of 46.9°C and after 180-min, a room temperature of 44.8°C was observed for end of treatment, 100% mortality was not obtained within 180-min time limit for this treatment (Tables 1 and 3).

Ventilation Shutdown With Supplemental Steam (VSD-S). The addition of steam in VSD-S resulted in a room temperature increase from 23.5°C to 39.3°C after 30-min (Table 3). Observed time to first mortality was at 55-min at a temperature of 44.8°C, whereas the observed time to one hundred percent mortality was achieved at 110-min at a temperature of 45.7°C (Tables 1 and 3). Room temperature steadily increased over the duration of VSD-S, reaching a maximum temperature of 47.2°C at approximately 175-min.

Ventilation Shutdown With Heat and Steam (VSD-HS). The room temperature for the times observed of first and 100% mortality were 48.4°C at 50-min and 47.0°C at 85-min (Tables 1 and 3). The room temperature increase in VSD-HS room was swift and the maximum temperature achieved was 49.5°C after steam was incorporated into the room for approximately 60-min (Table 3). This trial was stopped after 110-min due to 100% mortality achieved before 3-h limit, hence missing temperature data for this treatment in Tables 3 and 4.

Table 4. Relative humidity recorded for all VSD+ treatments.1

Empty Cell VSD+ treatments2 Empty Cell
Time (min) VSD-H VSD-S VSD-HS VSD-SH P-value
0 a59.3 ± 0.3 c78.7 ± 0.8 b70.6 ± 0.7 b67.8 ± 0.8 <0.001
5 70.4 ± 6.3 80.5 ± 1.0 71.4 ± 1.3 68.0 ± 1.0 0.278
10 a58.3 ± 0.7 c81.7 ± 0.7 b73.4 ± 1.3 c81.8 ± 5.3 <0.001
15 a59.9 ± 0.4 c99.2 ± 0.4 b71.1 ± 3.3 c98.3 ± 0.3 <0.001
20 a64.5 ± 1.1 b98.7 ± 0.7 a57.3 ± 5.2 b97.8 ± 0.3 <0.001
25 a50.4 ± 2.7 b98.3 ± 0.8 a46.9 ± 5.0 b97.0 ± 0.5 <0.001
30 a39.9 ± 2.6 b98.0 ± 0.8 a39.9 ± 4.4 b97.0 ± 0.5 <0.001
35 a33.8 ± 2.5 c97.8 ± 0.7 b67.4 ± 8.1 c96.8 ± 0.3 <0.001
40 a32.5 ± 2.6 b98.2 ± 0.7 b88.6 ± 5.1 b97.0 ± 0.5 <0.001
45 a36.0 ± 2.9 b98.3 ± 0.7 b95.5 ± 2.3 b97.0 ± 0.5 <0.001
50 a31.6 ± 2.6 b98.7 ± 0.6 b97.0 ± 1.3* b98.8 ± 0.8* <0.001
55 a32.5 ± 2.6 b99.2 ± 0.8 b97.1 ± 0.8 b97.5 ± 0.5 <0.001
60 a34.3 ± 2.5 b98.7 ± 0.7* b96.6 ± 0.9 b98.0 ± 0 <0.001
65 a35.9 ± 2.4 b99.2 ± 0.6 b95.1 ± 1.4 b98.0 ± 0 <0.001
70 a37.0 ± 2.3 b99.5 ± 0.5 b94.5 ± 1.2 b97.8 ± 0.3 <0.001
75 a37.8 ± 2.4 b99.5 ± 0.3 b94.4 ± 1.4 b97.8 ± 0.8 <0.001
80 a38.1 ± 2.2 b99.5 ± 0.3 b94.5 ± 1.4 b97.3 ± 1.3 <0.001
85 a38.3 ± 2.2* b99.5 ± 0.3 b94.9 ± 1.4⁎⁎ b95.8 ± 2.8 <0.001
90 a38.1 ± 2.1 b99.8 ± 0.2 b94.9 ± 1.4 b95.3 ± 3.3 <0.001
95 a38.3 ± 2.2 b99.8 ± 0.2 b94.8 ± 1.2 b94.5 ± 4.0 <0.001
100 a39.1 ± 2.4 c100 ± 0 b82.9 ± 1.9 b95.5 ± 3.0 <0.001
105 a42.4 ± 2.4 c100 ± 0 b71.0 ± 0.7 c95.8 ± 2.8⁎⁎ <0.001
110 a45.5 ± 2.5 c100 ± 0 b70.0 ± 0.4 c96.5 ± 2.0 <0.001
115 a45.0 ± 2.0 b100 ± 0⁎⁎ b97.3 ± 1.3 <0.001
120 a43.4 ± 1.9 b100 ± 0 b98.0 ± 1.0 <0.001
125 a42.9 ± 2.0 b100 ± 0 b98.3 ± 0.8 <0.001
130 a43.9 ± 2.2 b100 ± 0 b98.5 ± 0.5 <0.001
135 a46.6 ± 2.1 b100 ± 0 b98.5 ± 0.5 <0.001
140 a49.3 ± 1.9 b100 ± 0 b98.8 ± 0.3 <0.001
145 a50.1 ± 1.7 b100 ± 0 b98.8 ± 0.3 <0.001
150 a47.5 ± 1.6 b100 ± 0 b98.8 ± 0.3 <0.001
155 a45.1 ± 1.8 b100 ±0 b99.0 ± 0.5 <0.001
160 a43.5 ± 1.9 b100 ± 0 b99.3 ± 0.3 <0.001
165 a41.9 ± 1.9 b100 ± 0 b99.0 ± 0.5 <0.001
170 a43.3 ± 2.0 b100 ± 0 b99.3 ± 0.3 <0.001
175 a46.3 ± 2.1 b100 ± 0 b99.3 ± 0.3 <0.001
180 a48.9 ± 2.2 b100 ± 0 b99.3 ± 0.3 <0.001
1

Mean relative humidity (%) during VSD+ treatments. RH was measured every 30-s and means are based on average of 4 data loggers located throughout each room.

2

VSD-H= VSD+ heat only; VSD-S= VSD+ steam only; VSD-HS= VSD+ heat (for 30-min) and then steam; VSD-SH= VSD+ steam (for 30-min) and then heat.

a,b

Means± SEM within a column having different superscripts differ significantly (P < 0.05).

Indicates at what time and relative humidity the first observed mortality occurred for each VSD+ treatment.

⁎⁎

Indicates at what time and relative humidity 100% observed mortality occurred for each VSD+ treatment (VSD-H never reached 100% mortality).

Ventilation Shutdown With Steam and Heat (VSD-SH). When steam was utilized first, the temperature increased from 22.5°C to 40.5°C within 30-min (Table 3). After 30-min, the forced air heater (100,000 BTU) was turned on and room temperature rose to 45.5°C by 40-min. Temperature fluctuated between 43.8°C and 45.8°C, with 45.8°C being the maximum temperature attained towards end of treatment at approximately 170-min. Observed first mortality was recorded at a temperature of 43.8°C after 50-min, while 100% mortality was observed at 45.3°C after 105-min (Tables 1 and 3).

Relative Humidity

Commencing each treatment, out-of-doors average relative humidity for VSD-H, VSD-S, VSD-HS, and VSD-SH were 43.0%, 45.0%, 54.0%, and 49.0%, respectively, all below the 70% RH threshold (World Weather Forecast Service, n.d.). Table 4 indicates the relative humidity recorded during each VSD+ treatment. When analyzing relative humidity attained for VSD-H, VSD-S, VSD-HS, and VSD-SH there was a difference (P < 0.001) between treatments at each time point, with the exception of 5-min (Table 4). By 40-min, VSD-H had a lower relative humidity than all other treatments, and there was no difference between the treatments with steam (P < 0.0001).

Ventilation Shutdown With Supplemental Heat (VSD-H). For VSD-H, first mortality was observed at a relative humidity of 38.3% by 85-min, after 180-min, a relative humidity of 48.9% was observed for end of treatment, 100% mortality was not obtained within 180-min time limit for this treatment (Tables 1 and 4). At 5-min into treatment procedure, relative humidity quickly increased from 59.3% to 70.4%, with 70.4% being the highest obtained for VSD-H (Table 4). However, as it progressively got hotter in the room, relative humidity decreased to 39.9% after 30-min. After 70-min, relative humidity started to increase and reached 50.1% at approximately 145-min.

Ventilation Shutdown With Supplemental Steam (VSD-S). Initial relative humidity recorded for VSD-S was 78.7% and rose to 98.0% after 30-min of steam inclusion (Table 4). Throughout the treatment progression, relative humidity kept steadily increasing until 100% was achieved after 100-min. After 100% was achieved, relative humidity remained constant at 100% for the remainder of the procedure. When first mortality was observed at minute 55, the relative humidity was 98.7% and for 100% mortality it was 100% after 110-min (Tables 1 and 4).

Ventilation Shutdown With Heat and Steam (VSD-HS). Within 30-min of heat introduction in the VSD-HS room, relative humidity quickly decreased from 70.6% to 39.9% (Table 4). Then after 30-min, the heater was turned off and steam was administered into room. With 15-min of steam inclusion, relative humidity increased to 95.5%. After 55-min, a maximum relative humidity of 97.1% was achieved before slowly decreasing over duration of the treatment. Since 100% mortality was observed prior to the end of allotted 3-h time, treatment was ended after 110-min (hence missing relative humidity data). First and 100% mortality were observed at a corresponding relative humidity of 97.0% at 50-min and 94.5% at 85-min (Tables 1 and 4).

Ventilation Shutdown With Steam and Heat (VSD-SH). At 50-min into VSDS-SH, first mortality was observed at a relative humidity of 98.8%, while it took an extra 54-min for 100% mortality to be documented at a relative humidity of 95.8% (Tables 1 and 4). Since steam was utilized first, relative humidity quickly increased from 67.8% to 97.0% within 30-min (Table 4). After 30-min, steam pressure was decreased and forced air heater was turned on; relative humidity was elevated to 98.8% within 20-min of heater being on. In latter half of the treatment, relative humidity alternated between 95% and 98%, before reaching a maximum of 99.3% after 160-min.

In this study, steam was evaluated as a “plus” in ventilation shutdown for the depopulation of laying hens. Based on results, the hypothesis previously stated can be accepted since steam treatments were faster than VSD with heat alone in achieving the observed 100% mortality. During times of high heat and low relative humidity, animals can release heat quicker, while with high relative humidity, animal bodies cannot cool as efficiently. This statement is especially true in poultry that use evaporative cooling for heat removal. Authors Saeed et al. (2019) noted that when the temperature reached 35°C and relative humidity reached 40.0%, birds could remove 80.0% of total body heat through evaporative cooling, whereas at 35.0°C and 50.0% relative humidity, heat loss was reduced by 50%. However, when temperature remained at 35.0°C and relative humidity increased to 100%, birds could no longer remove body heat, causing chronic stress, shock, and high mortality (Saeed et al., 2019).

When poultry are exposed to high ambient temperatures and/or high relative humidity, birds will adjust their behavior and physiological needs to combat heat stress (Daghir, 2008). Qureshi (2001) observed laying hens’ reactions to different ambient temperatures and relative humidity. According to the author, hens were undisturbed between 20.0°C and 25.0°C when relative humidity was 75.0%. However, when temperatures reached between 30.0°C and 35.0°C and relative humidity increased to 100%, hens were moderately disturbed while in temperatures beyond 40.0°C with a relatively humidity of 100%, hens were extremely disturbed, and death occurred (Qureshi 2001). Results from the present study concurred with observations from Qureshi (2001) since recorded temperatures for all treatments were above 40°C; although, steam treatments were the only ones capable of reaching a relative humidity in the 90% to 100% range, resulting in 100% mortality. Treatment VSD-H was unable to reach 100% mortality in 3-h, which may be due to the treatment being unable to reach a high enough relative humidity throughout procedure, probably because hens were able to still dissipate heat during the observed high temperatures. Lee et al. (1945) noted several relationships between temperature and relative humidity that should be worthy of consideration. When relative humidity is kept at 75% or less, hens can tolerate a temperature of 37.8°C or above for a 7-h period (Lee et al., 1945). Additionally, if temperature increases to 40.6°C, hens can tolerate this temperature for only a few hours regardless of the relative humidity, however, relative humidity becomes an essential factor for hen survival in temperatures of 40.6°C and above (Lee et al., 1945).

Moreover, it is essential to recognize that by the time the first mortality was observed for VSD-H, all VSD+ treatments that utilized steam had already achieved their first observed mortality approximately 30-min faster. VSD-HS was the quickest to achieve 100% observed mortality; this was also approximately at the same time that the first observed mortality was recorded for VSD-H. VSD-HS and VSD-SH first mortality was observed at approximately the same time, within 2-min of each other. These results indicate that ventilation shutdown with steam inclusion was a more effective way to depopulate laying hens than VSD with supplemental heat only. When supplemental heat was utilized first, coupled with steam addition after 30-min, a quicker time to mortality was achieved (100% observed mortality in less than 90-min).

Furthermore, all VSD+ treatments were able to achieve the AVMA-required temperature of 40.0°C and remained comparable between one another throughout the 3-h limit, with little variation in temperature. However, when comparing the relative humidity table between treatments, variability was apparent. In VSD-S, when only steam was utilized, relative humidity increased rapidly, close to 100%, and maintained stable throughout the duration of the procedure and VSD-SH followed a similar trend. For VSD-HS, a distinction in relative humidity can be made when steam was administered into room, when relative humidity rapidly increased from 39.9% to 67.4% after 5-min of steam addition, while relative humidity decreased over time when only supplemental heat was used (VSD-H). A simultaneous rise in both room temperature and relative humidity likely contributed to hen’s inability to properly remove body heat through evaporative cooling.

In the current study, VSD+ treatments that utilized steam were able to achieve both high ambient temperature and relative humidity, thus leading to a much faster observed time to death than when only high ambient temperature was achieved in VSD-H. These findings agree with previous research that high relative humidity, along with elevated temperatures, are both crucial in attaining 100% mortality during ventilation shutdown (Zhao et al., 2019). Additionally, results from present study concurred with Baysinger et al. (2021), showing the addition of steam to be effective and essential in the success of ventilation shutdown. Together, these findings could potentially aid utilization of VSD+ for mass depopulation in the event of a foreign animal disease outbreak or severe market disruption (Baysinger et al., 2021). Moreover, the current findings for observed times to 100% mortality are comparable to published results obtained from ventilation shutdown with carbon dioxide (Eberle-Krish et al., 2018). Steam usage has advantages compared to CO2, such as worker safety, possibly lower cost, and there are minimal concerns for steam shortage as experienced with CO2 shortages (Eberle-Krish et al., 2018; CGA, n.d.; HSE, n.d.; Burgess, 2022).

CONCLUSIONS AND APPLICATIONS

  • 1.

    Steam alone, or in combination with heat, demonstrated to be effective as a “plus” in ventilation shutdown for the depopulation of laying hens in a cage-free aviary system based on observed time to 100% mortality.

  • 2.

    Steam usage could potentially eliminate environmental differences to allow for a more uniform mortality spread and perhaps make VSD+ more consistent since steam was capable of causing a simultaneous rise in room ambient temperature and relative humidity.

  • 3.

    When comparing published data available for VSD+ CO2, addition of steam to a VSD+ procedure would be beneficial in times when CO2 is unavailable since steam had comparable mortality times to VSD with CO2.

  • 4.

    While data from present study gives an insight to how successful steam addition is during VSD+ depopulation, more research must be conducted in a commercial environment to explore depopulation with steam outside experimental conditions.

ACKNOWLEDGMENTS

This research was funded by Michigan Alliance for Animal Agriculture (grant number AA-19-050).

DISCLOSURES

The authors declare no conflict of interest to disclose.