Clifton, V.L., Moss, T.J.M., Wooldridge, A.L., Gatford, K.L., Liravi5, B., Kim, D., Muhlhausler, B.S., Morrison, J.L., Davies, A., De Matteo, R., Wallace, M.J., & Bischof, R.J. 2015. ‘Development of an experimental model of maternal allergic asthma during pregnancy’. Journal of Physiology. doi: 10.1113/JP270752.
Associated Institutions: The University of Adelaide, Monash University, University of Queensland
In an attempt to investigate the mechanisms underlying fetal effects of maternal asthma in pregnancy, researchers conducted an experiment on 40 pregnant sheep.
The sheep (merino ewes), 1-2 years old, were randomly allocated to test (sensitised, n=31) and control (non-immunised, n=9) groups.
Sheep in the sensitised group were immunised with house dust mites (HDM) using four injections of solubilised HDM extract, with injections given at 2 week intervals. Blood samples were collected from both sensitised and non-immunised sheep by venepuncture prior to the immunisation regime, as well as 7 days afterwards.
The blood samples were then used to assess whether sheep were allergic, and sheep were reallocated to groups accordingly: non-allergic control group (n=13), and allergic ewes test group (n=17).
All 30 sheep then underwent weekly endoscopic airway challenges for 8 weeks. The allergic sheep were exposed to 1mg HDM in saline, while the control group sheep was exposed to just saline. These ‘airway challenges’ involved sheep being restrained unsedated in a body harness, while an endoscope was inserted into the lung via the nasal passage so that saline or HDM in saline could be delivered to the lungs.
Fluid samples were collected at various stages via a ‘broncho-alveolar lavage’ procedure, whereby a bronchoscope is passed through the mouth or nose into the lungs and fluid is squirted into a small part of the lung and then collected for examination.
Following the 8 weeks of airway challenges, ewes had their oestrous cycles synchronised using intravaginal sponges for 12 days, and were then mated with rams. Pregnancy was then determined by ultrasound. This resulted in a control group of 9 pregnant sheep, and an allergic test group of 11 pregnant sheep.
Surgery was performed on the 20 sheep, after food was withheld for 24 hours. Under general anaesthesia, an indwelling catheter (a tube that is fixed in the body for a sustained period of time) was placed into the maternal and fetal carotoid arteries and jugular veins (in the neck) and amniotic fluid, in order to enable physiological responses to airway challenges to be recorded.
Further endoscopic airway challenges took place throughout pregnancy. The allergic sheep were exposed to 1mg HDM in saline every two weeks, while the control group sheep was exposed to just saline every four weeks.
Airway challenges at mid and late pregnancy were delivered as aerosols. In a similar way as described above, sheep were restrained unsedated in a custom-made sling. Aerosolized HDM extract (for allergic sheep) or saline (for control sheep) was delivered via nebulisation for 15 minutes at 20 breaths per minute. To measure lung resistance, oesophageal and tracheal catheters were placed into the lung via the nostrils, with an endoscope used for guidance.
Eight sheep were ‘lost to the study‘. Causes include: 1 non-pregnancy (detected at surgery), 1 ‘sick on farm’, 1 ‘failure to recover post-surgery’, 1 fetal death, and 4 premature deliveries.
The remaining 12 sheep (control group = 5, allergic test group = 7) were killed by an overdose of sodium thiopentone at 138-142 days pregnant (gestational age), i.e. fetuses were a few days shy of full term. Fetuses were then removed and weighed. Maternal and fetal lung, heart, liver, kidneys, spleen, brain and fat depots were also dissected, weighed, and examined.
The study publication does not detail what happened to the other 20 sheep that were involved in the study but did not progress to post-mortem.
The researchers claimed that their experiment showed that allergic asthma in pregnant sheep modifies placental phenotype, and inhibits fetal growth and lung development. The researchers also suggest that they will continue with future, larger studies using sheep to study asthmatic pregnancies.
Animal Welfare Concerns
The researchers state that the sheep were housed outdoors in small paddocks during allergen sensitisation and airway challenges, but that from 90-100 days into their pregnancy they were housed indoors in individual pens for 40-50 days, until they were killed at the end of the experiment. Housing the sheep – especially pregnant sheep under extra stress – in small, enclosed spaces without outside access for extended periods of time raises serious welfare concerns.
Also of serious concern is the impaired nutrient and/or oxygen supply experienced by the mother sheep and their fetuses during pregnancy.
The researchers claim that it is “ethically impossible” to conduct experiments such as this one on women. However, the same ethical concerns that exist in relation to a human study being conducted are also relevant to sheep.
Sheep are highly sentient beings capable of pain and suffering. Studies have shown that sheep are intelligent and emotional creatures, which have a remarkable memory for faces and even form mental images of missing companions.1
Relevance to Humans
There are major anatomical, genetic, dietetic, environmental, toxic, and immune differences between animals – including sheep – and humans2, making them inappropriate for use in studying human disease such as maternal allergic asthma during pregnancy. Many studies and systematic reviews show that there is discordance between animal and human studies, and that animal ‘models’ fail to mimic clinical disease adequately.3,4 In fact, in relation to the specifics of this study, scientists acknowledge that ‘no animal model truly recapitulates human pregnancy’.5
Within the research publication itself, the researchers also highlight that airway structure and function in animals (mice) is poorly aligned to the human lung. The utility of the experiment is questionable given the uncertainty around extrapolating results from any animal, including sheep, to humans.
Given that asthma is one of the most common chronic diseases to affect pregnant women, one must seriously question why the researchers engaged in this study did not utilise a human sample to study this area, and/or advanced human biology-based methods of research, in order for results to be directly relevant to human health outcomes.
Furthermore, to add insult to injury, the researchers also note that there is already “a well-established association between maternal asthma and adverse pregnancy outcomes” that has been evidenced in human clinical trials.6
The experiment received funding from the Jack Brockhoff Foundation, the Victorian Government Operational Infrastructure Support Program. Various authors were publicly funded through NHMRC Senior Research Fellowships, NHMRC Career Development Fellowships, and Australian Postgraduate Awards.
What You Can Do
Please use the form below to tell the University of Adelaide and Monash University how disappointed you are with their use of animals in this experiment. You can use the text provided or compose your own. Remember, personalised emails and subject lines carry more weight.
Your message will be sent via email to the Vice-Chancellor of the University of Adelaide, and the Executive Assistant to the Vice-Chancellor of Monash University.
1 Kendrick, K., da Costa, A.P., Leigh, A.E., Hinton, M.R. & Peirce, J.W. 2001. ‘Sheep don’t forget a face’, Nature, 414, 165-166.
2 Pound P, Ebrahim S, Sandercock P, Bracken MB, Roberts I; on behalf of the Reviewing Animal Trials Systematically Group. 2004. ‘Where is the evidence that animal research benefits humans?’, BMJ, 328, 514-7.
3 Perel P, Roberts I, Sena E, Wheble P, Briscoe C, Sandercock P, et al. 2007. ‘Comparison of treatment effects between animal experiments and clinical trials: systemic review’, BMJ, 334:197.
4 Van der Worp H, Howells DV, Sena ES, Porritt MJ, Rewell S, O”Collins V, et al. 2010. ‘Can animal models of disease reliably inform human studies?’, PLoS Med.
5 Barry, J.S. & Anthony, R.V. 2008 ‘The Pregnant Sheep as a Model for Human Pregnancy’. Theriogenology, Jan 1; 69(1): 55–67.
6 Page 4. Clifton, V.L., Moss, T.J.M., Wooldridge, A.L., Gatford, K.L., Liravi5, B., Kim, D., Muhlhausler, B.S., Morrison, J.L., Davies, A., De Matteo, R., Wallace, M.J., & Bischof, R.J. 2015. ‘Development of an experimental model of maternal allergic asthma during pregnancy’. Journal of Physiology.