PHYSIOLOGY, ENDOCRINOLOGY, AND REPRODUCTION
Evaluation of the diving reflex in response to nonterminal submersion
of White Pekin ducks in water-based foam
M. P. Caputo,* R. L. Alphin,* E. Pritchett,* D. P. Hougentogler,* A. L. Johnson,†
E. R. Benson,*1 and C. Patil‡
*Department of Animal and Food Sciences, University of Delaware, Newark 19716;
†Department of Clinical Studies–New Bolton Center, University of Pennsylvania School of Veterinary Medicine,
Kennett Square 19348; and ‡Applied Economics and Statistics, University of Delaware, Newark 19716
ABSTRACT The mass depopulation of production
birds remains an effective means of controlling fastmoving, highly infectious diseases such as avian influenza and virulent Newcastle disease. Water-based firefighting foam is a conditionally approved method of
depopulating floor-reared gallinaceous poultry such as
chickens and turkeys; however, ducks have physiological mechanisms that may make them more resistant to
this method of depopulation. The following experiment
was designed to assess the physiological responses of
White Pekin ducks to nonterminal submersion in water-based foam compared with water. The hypothesis of
this experiment was that submersion of ducks in water
or water-based foam would trigger the diving reflex and
lead to bradycardia. All treatments led to pronounced
bradycardia. Heart rate was not significantly different
between treatments during the final 30 s of the 60-s
treatment period. Heart rate dropped significantly faster for the water dip and foam dip treatments and rose
significantly faster than the foam pour treatment after
the termination of the 60-s treatment period. Duration
of bradycardia approached significance for the foam
pour treatment, leading to a longer duration of bradycardia compared with the water pour, water dip, and
foam dip treatments. The results of this experiment
demonstrated that apnea and bradycardia as a result
of the diving reflex can occur as a result of submersion
in foam, which may have an impact on the time it takes
White Pekin ducks to reach unconsciousness and death
during water-based foam depopulation.
Key words: foam, duck, depopulation, bradycardia, diving reflex
2013 Poultry Science 92:412–417
http://dx.doi.org/10.3382/ps.2012-02513
INTRODUCTION
cluded several different types of poultry and game birds
including broilers, layers, turkeys, chukars, Japanese
quail, call ducks, and White Pekin ducks. Water-based
foam as a method of mass depopulation of floor-reared
poultry was conditionally approved by the USDA-Animal and Plant Health Inspection Service (APHIS) and
the American Veterinary Medical Association in 2006
(AVMA, 2006).
Although water-based foam is an effective means of
depopulation for gallinaceous species (Dawson et al.,
2006; Benson et al., 2007, 2009; Alphin et al., 2010; Flory and Peer, 2010; Rankin, 2010), there has been some
concern that ducks may be able to withstand hypoxia,
which is the mechanism by which foam induces death.
Ducks are known to have a diving reflex, by which apnea causes bradycardia, which is naturally triggered by
submersion in water (Butler and Taylor, 1973; Bamford
and Jones, 1974). Bryan and Jones (1980) determined
that bradycardia was an oxygen-conserving cardiovascular adjustment that played a key role in increased
tolerance to asphyxia, which is important for diving
species. Having water in contact with the beak, na-
The possibility of an outbreak of highly pathogenic avian influenza, or virulent Newcastle disease is an
ongoing concern for the poultry industry. When outbreaks of highly pathogenic avian influenza occur, the
affected farms require depopulation (culling) of all infected, exposed, or potentially infected birds (USDA,
2007). Depopulation may also be required in the event
of a natural disaster or structural damage to the facility. In the event that a flock needs to be depopulated,
it is important to balance safety and efficiency with the
welfare of the birds. Previous studies by Benson et al.
(2007, 2009) and Alphin et al. (2010) compared the effectiveness of CO2 gassing to water-based foam for the
depopulation of floor-reared poultry. These studies in-
©2013 Poultry Science Association Inc.
Received June 5, 2012.
Accepted October 8, 2012.
1 Corresponding author: [email protected]
412
NONTERMINAL SUBMERSION OF DUCKS IN FOAM
res, or internal respiratory passages is not necessary to
elicit a diving-type response, but rather it is the apnea
itself that triggers the bradycardia seen during the diving reflex (Butler and Taylor, 1973). If foam contact
with the beak, nares, or respiratory passages is sufficient to elicit the diving reflex, ducks undergoing foam
depopulation may undergo a period of bradycardia that
allows them to withstand a longer period of asphyxia
and hence increases time to unconsciousness and death.
A previous study by Benson et al. (2009) showed
that foam can be successfully used to depopulate
ducks; however, cessation time was collected through
motion cessation, and the time it took for the animals
to reach unconsciousness and brain death could not be
calculated from the motion cessation data. This study
also found that the motion cessation times for ducks
as measured by an accelerometer were comparatively
longer than chukars, broilers, and quail depopulated in
foam in a similar manner (Benson et al., 2009). Ducks
have physiological differences from gallinaceous birds,
as described above, which some studies suggest makes
them more difficult to depopulate (Raj, 2008), whereas
others found that there was no significant difference
in their ability to withstand hypoxia (Gerritzen et al.,
2006). It is therefore important to further investigate
the physiological responses of ducks to water-based
foam depopulation to ensure the welfare of the animal.
The following experiment aimed to test the hypothesis
that temporary submersion of White Pekin ducks in
water-based foam would trigger the diving reflex and
lead to bradycardia.
MATERIALS AND METHODS
General Procedure and Instrumentation
Eight straight run White Pekin ducks were obtained
from a commercial hatchery (Metzer Farms, Gonzales,
CA) and raised following standard care and conditions.
The ducks were raised on litter and were allowed access to commercial feed and water ad libitum. To measure electrical cardiac activity, each duck was instrumented with electrocardiogram (ECG) electrodes and
leads (BIOPAC Systems Inc., Goleta, CA) placed on
a previously plucked area on each leg and underneath
the right wing. The ECG signals were recorded using
BIOPAC Student Lab (BSL) software and processed
through a BIOPAC Systems Inc. MP30A acquisition
unit. Analysis of the ECG signals was conducted using BIOPAC BSL Pro to analyze the recorded signals
and find critical points. Critical points included onset
and cessation of bradycardia. Bradycardia was defined
for analysis purposes in this study as a heart rate that
dropped to 100 beats per minute (bpm) or less and
sustained the lowered rate for at least 10 consecutive
seconds, followed by a return to a rate in excess of 100
bpm. A heart rate of 100 bpm was selected because it
represented an approximately 50% reduction in normal
413
heart rate, which would meet the definition of bradycardia.
Foam Treatments
For the foam treatment, water-based foam with ambient air was created using a nozzle type foam depopulation system (model AG-1, Spumifer, Ridgefield Park,
NJ). This system draws air through the rear of the
nozzle and combines it with a mixture of the foam concentrate and water. A 1% solution of foam concentrate
(WD-881, Phos-Check, St. Louis, MO) and water was
premixed on the day of trial. A Darley water pump
(model 2 1/2 AGE 31 BS, Darley, Itasca, IL) was used
to supply the required pressure and flow. The pump
was driven by a 23-kW (31 hp) gasoline engine (Briggs
and Stratton Vanguard, Milwaukee, WI), which provided a rated performance of 1,136 L/min (300 gal/
min) at 586 kPa (85 psi). This foam system meets
the USDA-APHIS conditional requirements for waterbased foam depopulation. All testing was performed
under the approval and guidelines of the University of
Delaware Agricultural Animal Care and Use Committee and followed the guidelines laid out by the Federation of Animal Science Societies (FASS, 2010).
Evaluation of the Diving Reflex
For this experiment, a total of 8 White Pekin ducks,
8 to 11 wk old, were instrumented with ECG leads
as described above. The ducks were restrained horizontally, ventral side down in a wooden cradle using a
full-body-length custom restraint jacket. A hood was
placed over the ducks’ eyes to reduce movement and
prevent anticipation of any treatment. A baseline of
420 s was established. After this point, the duck was
exposed to 1 of 4 random treatments as determined
by a randomization table created in Excel (Microsoft
Corp., Redmond, WA). The treatments were (1) water
dip (WD), (2) foam dip (FD), (3) water pour (WP),
or (4) foam pour (FP). The bill was submerged by
lowering the head into a container of either water (1) or
foam (2) so that the nares were covered for 60 s. Water
(3) or foam (4) was poured over the bill, flowing over
the nares for the full 60-s treatment period.
For the foam pour and water pour treatments, foam
or water was poured into a 208-L drum using the hose
from the foam system and situated on a platform above
the duck. The 208-L drum was fitted with a sliding
lever that allowed the foam or water to achieve a continuous flow rate of 13.3 L/min over the 60-s treatment
period.
The ducks were given at least 1 h between tests to
recover. A recovery time of 1 h was chosen because a
previous study found that White Pekin ducks that were
forced to dive for times ranging between 60 and 900 s
showed no physiological injury as demonstrated by the
heart rate, blood pressure, ECG, and EEG returning to
414
Caputo et al.
predive levels by the time a second endurance dive was
initiated 1 h later (Hudson and Jones, 1986). The ducks
were closely monitored and submerged for a maximum
of 60 s and were immediately removed if respiration
continued while the ducks were submerged. During the
course of this experiment, however, no ducks attempted
respiration while submerged. After 60 s of submersion,
the ducks were monitored during recovery for an additional 420 s, for a total recording time of 900 s. The
900-s recording period for this experiment was broken
into 8 critical time periods for analysis. The time periods were based on relation to the treatment period: the
first 60 s of pretreatment (0 to 30 s and 30 to 60 s), the
last 30 s of pretreatment (390 to 420 s), the treatment
period (420 to 450 s and 450 to 480 s), the first 30 s of
posttreatment (480 to 510 s), and the last 60 s of the
posttreatment period (840 to 870 s and 870 to 900 s).
For this experiment, there were 2 groups of 4 ducks,
for a total of 8 ducks, and each duck was randomly
assigned to treatment; however, the treatment assignment was not balanced. A total of 65 trials were
completed with the FP treatment having 15 trials, FD
treatment 17 trials, WD treatment 17 trials, and WP
treatment 16 trials. The mean heart rate for each 30-s
interval was calculated for each duck, and these means
were averaged for each of the 4 treatments. In addition to analyzing the effect of submersion of the ducks’
bills in foam or water on heart rate, the duration of
bradycardia caused by contact with foam or water was
also analyzed. Statistical analysis was performed using
JMP (SAS Institute Inc., Cary, NC) using the Fit Model for each time period with treatment and duck as a
random variable. Because an unbalanced Block Design
was used, ducks were included in the mixed model as a
block factor with random effect. Data presented were
calculated as means ± SEM based on pooled variance.
Each time period was considered a separate model
without repeated measures. Multiple comparisons were
performed using the Tukey-Kramer honestly significant
difference test (P = 0.05). The analysis was verified using SAS as PROC GLM, least squares means, with the
Tukey comparison option.
RESULTS
Figure 1 below shows that all 4 treatments caused a
drop in heart rate that met the definition of bradycardia. As seen in Table 1, no differences occurred in heart
rate between treatment groups during the pretreatment
periods (0 to 30 s, 30 to 60 s, and 390 to 420 s; P
> 0.05). Additionally, no differences in heart rate occurred across treatment groups for FP and WP or FD
and WD at any point during the trial period.
There was an effect of different treatments on heart
rate during the treatment periods as shown in Figure 1
and Table 1. There were no differences during pretreatment (0 to 30 s, 30 to 60 s, 390 to 420 s). During the
first 30 s of treatment (420 to 450 s), differences oc-
Figure 1. Mean heart rate of White Pekin ducks (n = 8) that had foam (FP, n = 15) or water (WP, n = 16) poured on their bills or had their
bills dipped in foam (FD, n = 17) or water (WD, n = 17). For analysis purposes, the trial was broken into 8 critical periods over the 900-s trial.
415
NONTERMINAL SUBMERSION OF DUCKS IN FOAM
Table 1. Mean heart rate of White Pekin ducks in beats per minute, analyzed in 30-s intervals of a 900-s recording
Treatment1,2
Time
period (s)
0 to 30
30 to 60
390 to 420
420 to 450
450 to 480
480 to 510
840 to 870
870 to 900
FP
174.1
176.5
185.6
145.5
53.0
88.4
186.8
188.4
±
±
±
±
±
±
±
±
11.2a
9.9a
9.6a
11.1ab
6.3a
17.5c
12.3a
13.1a
FD
182.9
174.5
187.5
115.0
55.6
201.6
163.8
172.9
±
±
±
±
±
±
±
±
10.8a
9.6a
9.4a
10.8c
5.9a
16.5a
12.1b
12.9a
WP
179.2
175.9
189.6
156.5
59.7
134.6
182.0
180.0
±
±
±
±
±
±
±
±
10.9a
9.7a
9.5a
10.9a
6.0a
18.6bc
12.2ab
13.0a
F3
WD
178.1
176.5
200.9
121.1
54.5
173.6
170.8
175.5
±
±
±
±
±
±
±
±
10.7a
9.5a
9.3a
10.7bc
5.8a
16.6ab
12.0ab
12.8a
0.257 (P = 0.856)
0.027 (P = 0.994)
1.547 (P = 0.212)
9.64 (P = 0.001)
0.312 (P = 0.817)
9.01 (P < 0.001)
3.06 (P = 0.036)
1.27 (P = 0.294)
a–cMeans
within a row with different superscripts differ (P < 0.05) using Tukey’s honestly significant difference test.
FP = foam pour; FD = foam dip; WD = water dip; WP = water pour.
2Data presented as mean ± SEM based on pooled variance.
3F-test based on PROC MIXED and least squares means for the treatment. The model adjusts for duck as a random block.
1Treatments:
curred between FD and FP and between FD and WP.
During the second 30 s of treatment (450 to 480 s),
there were no differences between heart rates by treatment. During the first 30 s of recovery (480 to 510 s),
there were differences FD and FP, FD, and WP, and
FP and WD. By the conclusion of recovery (870 to 900
s), there were again no differences in heart rate.
Figure 2 shows that there was some effect on duration of bradycardia across treatments. The FP treatment had an effect on the duration of bradycardia that
approached significance (P = 0.059).
DISCUSSION
The purpose of this experiment was to determine if
submersion of the bill in foam causes bradycardia or
other cardiac patterns similar to submersion in water,
as well as to provide a baseline to measure future cardiac adjustments compared with bradycardia produced
Figure 2. Mean duration of bradycardia observed in White Pekin
ducks (n = 8) for each of the submersion treatments: foam dip (FD,
n = 17), foam pour (FP, n = 15), water dip (WD, n = 17), and water
pour (WP, n = 16). Error bars represent SEM. Different letters above
SE bars denote statistical significance between treatments (α = 0.05).
The FP treatment (P = 0.059) approached significance.
by submersion of the bill in water. In addition, this
experiment sought to determine if static contact of the
bill in foam was sufficient to trigger the duck to voluntarily cease respiration and cause bradycardia. All of
the ducks tested using the treatments FP, FD, WP, and
WD developed bradycardia during the 60-s treatment
period, which occurred between 420 and 480 s. The results showed that there was no difference between any
of the treatments during the final 30 s of the treatment
period (450 to 480 s), suggesting that all treatments
caused a similar level of bradycardia. During the posttreatment recovery phase (480 to 510 s), there were
differences between treatments.
Figure 1 shows that FD caused lower heart rates during the first 30 s of the treatment period (420 to 450
s) as opposed to FP and WP. In addition, during the
same time period, WD had a lower heart rate than WP.
These results in connection suggest that the action of
dipping the bill in water or foam lead to a faster induction of bradycardia as compared with pouring water
or foam over the bill. The FP treatment resulted in
a lower heart rate during the first 30 s of the posttreatment period (480 to 510 s) compared with FD and
WD. The WP resulted in a lower heart rate during
this period (480 to 510 s) compared with FD. By the
final period of posttreatment recovery (870 to 900 s),
all treatments showed minimal differences, indicating
that once removed from foam, birds would recover similarly to birds exposed to water. Additionally, the FP
treatment caused a longer duration of bradycardia than
the FD, WD, and WP treatments, which approached
statistical significance (Figure 2). This may be due to
the tendencies of the foam to stick to the bill after the
foam stopped pouring, which likely led to a continued
response.
Because there was no difference in heart rate between
the 2 pour treatments (FP and WP) and the 2 dip
treatments (FD and WD), it can be concluded that the
mechanism by which the foam or water was applied to
the bill made a greater difference in heart rate drop and
recovery as opposed to the type of liquid. These results
are important because they show that heart rate can
416
Caputo et al.
be affected when pouring foam directly over the ducks’
heads individually, as in small-chamber, laboratory depopulation compared with foam rising from the ground
and building above the birds’ heads. In the field, foam
is typically directed onto the ground or the sidewall of a
pen or building and allowed to build up to a level above
the birds’ heads (Benson et al., 2009; Simunich, 2009),
which may mimic the bill being dipped into foam because the foam is not applied directly to the ducks.
Based on the graph shown in Figure 1, foam depopulation in which foam is applied directly to the ducks’
bodies or bills would most likely result in a delayed diving response, whereas a situation where the foam was
allowed to slowly engulf the ducks would most likely
result in an earlier diving response, as soon as the bill
was dipped into the foam. Equally important, the information in Figure 2 shows that FP caused a prolonged
duration of bradycardia compared with FD, despite
equal treatment times.
It is important to note that all ducks that were tested
survived the submersion in both water and foam. This
experiment has demonstrated that submersion of White
Pekin ducks in both foam and water leads to an initial
apnea followed by bradycardia that lasted between 8
and 294 s, even though the bill was removed from the
foam after 60 s. Other instances of bradycardia not
associated with the diving reflex have been reported
during euthanasia and depopulation of ducks as well
as gallinaceous birds (Gerritzen et al., 2006; McKeegan
et al., 2011). Bradycardia occurs when the concentration of CO2 in the surrounding air rises, such as during
gas depopulation, which typically leads to cardiac arrhythmias and death (Gerritzen et al., 2006; McKeegan
et al., 2011). Apnea was reported in ducks that were
exposed to and survived CO2 concentrations between
5 and 20% in an enclosed chamber (Orr and Watson,
1913); it was later found that this response was caused
by the irritant properties of the gas itself (Dooley and
Koppanyi, 1929). However, the bradycardia observed
when the ducks’ bills are submerged in foam and water is different from the above situations in that high
concentrations of CO2 gas were not inhaled and all of
the ducks recovered. Submersion in foam, therefore, initially triggers apnea, as opposed to apnea caused by
the foam occluding the trachea, and has similar cardiac effects to submersion in water. It can therefore be
concluded that foam depopulation, because it involves
full submersion in water-based foam, triggers a diving
reflex in White Pekin ducks.
The depopulation of production birds is an effective and important method of preventing the spread
of highly infectious diseases. A previous experiment
by Benson et al. (2009) showed that water-based foam
was an effective and efficient means of depopulation,
even for White Pekin ducks. During an outbreak of
low pathogenic avian influenza on a game bird farm
in Idaho, water-based foam was used to successfully
depopulate ducks that were living in pens and open-air
structures that could not be sealed for CO2 gas depopulation (Simunich, 2009). A possible drawback of using
water-based foam to depopulate White Pekin ducks
is that this experiment supports the hypothesis that
water-based foam does cause an initial period of apnea
and bradycardia. Further testing is required to determine if this apnea and bradycardia due to the diving
reflex prolongs the time to unconsciousness and death
during foam depopulation.
ACKNOWLEDGMENTS
This research was supported by USDA-APHIS (106100-0032-GR and 2011-67022-30339) and the University of Delaware College of Agriculture and Natural Resources. The authors also thank University of Delaware
undergraduate research students Erik Herrman, Carolyn Kinney, James McGurk, Joseph Kelderhouse, and
Nola Parcells for their contributions to this project.
The authors acknowledge the modeling and analysis
support of the University of Delaware STATLAB.
REFERENCES
Alphin, R. L., E. R. Benson, K. J. Johnson, and M. K. Rankin.
2010. Comparison of water-based foam and inert-gas mass emergency depopulation methods [electronic resource]. Avian Dis.
54(s1):757–762. http://dx.doi.org/10.1637/8764-033109-Reg.1.
AVMA (American Veterinary Medical Association). 2006. Use of
water-based foam for depopulation of poultry. Am. Vet. Med.
Assoc. 1–4. https://www.avma.org/KB/Policies/Pages/PoultryDepopulation.aspx.
Bamford, O. S., and D. R. Jones. 1974. On the initiation of apnoea and some cardiovascular responses to submergence in ducks.
Respir. Physiol. 22:199–216.
Benson, E. R., G. W. Malone, M. D. Dawson, and R. L. Alphin.
2009. Use of water-based foam to depopulate ducks and other
species. Poult. Sci. 88:904–910.
Benson, E. R., C. R. Pope, G. L. Van Wicklen, M. D. Dawson, G.
W. Malone, and R. L. Alphin. 2007. Foam-based mass emergency depopulation of floor-reared meat-type poultry operations.
Poult. Sci. 86:219–224.
Bryan, R. M. J., and D. R. Jones. 1980. Cerebral energy metabolism
in Mallard ducks during apneic asphyxia: The role of oxygen
conservation. Am. J. Physiol. 239:R352–R357.
Butler, P. J., and E. W. Taylor. 1973. The effect of hypercapnic
hypoxia, accompanied by different levels of lung ventilation, on
heart rate in the duck. Respir. Physiol. 19:176–187.
Dawson, M. D., E. R. Benson, G. W. Malone, R. L. Alphin, I. Estevez, and G. L. Van Wicklen. 2006. Evaluation of foam-based
mass depopulation methodology for floor-reared meat-type poultry operations. Appl. Eng. Agric. 22:787–794.
Dooley, M. S., and T. Koppanyi. 1929. The control of respiration
in the domestic duck (Anas boscas). J. Pharmacol. Exp. Ther.
36:507–518.
FASS. 2010. Guidelines for the Care and Use of Animals in Agricultural Research and Teaching. 3rd ed. Fed. Anim. Sci. Soc.,
Champaign, IL.
Flory, G. A., and R. W. Peer. 2010. Verification of poultry carcass
composting research through application during actual avian influenza outbreaks. ILAR J. 51:149–157.
Gerritzen, M. A., B. M. Spruijt, J. A. Stegeman, E. Lambooij, and
H. G. M. Reimert. 2006. Susceptibility of duck and turkey to
severe hypercapnic hypoxia. Poult. Sci. 85:1055–1061.
Hudson, D. M., and D. R. Jones. 1986. The influence of body mass
on the endurance to restrained submergence in the Pekin Duck.
J. Exp. Biol. 120:351–367.
NONTERMINAL SUBMERSION OF DUCKS IN FOAM
McKeegan, D. E. F., N. H. C. Sparks, V. Sandilands, T. G. M.
Demmers, P. Boulcott, and C. M. Wathes. 2011. Physiological
responses of laying hens during whole-house killing with carbon
dioxide. Br. Poult. Sci. 52:645–657. http://dx.doi.org/10.1080/
00071668.2011.640307.
Orr, J. B., and A. Watson. 1913. Study of the respiratory mechanism
in the duck. J. Physiol. 46:337–348.
Raj, M. 2008. Humane killing of nonhuman animals for disease control purposes. J. Appl. Anim. Welf. Sci. 11:112–124.
Rankin, M. K. 2010. Comparison of water-based foam and inert gas
emergency depopulation methods of turkeys. MS Thesis. University of Delaware, Newark.
417
Simunich, M. M. 2009. H5N8 LPAI in an Idaho game bird farm–
2008. Proceedings of the USAHA/AAVLD Committee on Animal
Emergency Management. San Diego, CA. United States Animal
Health Association, St. Joseph, MO.
USDA. 2007. Summary of the National Highly Pathogenic Avian Influenza (HPAI) Response Plan. USDA Animal and Plant Health
Inspection Service Veterinary Services, Washington, DC.