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Why do some broilers have gait problems and how does it affect them?

Researchers from Aarhus University are among the first to focus on causes and effects of impaired walking ability, that is not decidedly lameness, in conventional broilers.

[Translate to English:] Ph.d.-studerende Atefeh Berenjian (t.v.) og bachelorstuderende Maud van der Brand vejer slagtekyllinger som led i undersøgelse af kyllingernes gangegenskaber. I baggrunden bliver kyllingernes gangegenskaber evalueret. Foto: Anja Brinch Riber

What is the reason that some conventional broilers have impaired walking ability and does it affect their health and welfare? The Danish Veterinary and Food Administration has requested researchers from Aarhus University to elucidate this with the aim of optimising broiler welfare. 

A considerable proportion of broilers have impaired walking abilities and many broilers walk poorly without actually being lame. The poultry industry and researchers have had their focus on broiler walking ability for a long time in order to monitor development and take action when necessary. 

Gait is quantified

The internationally applied Bristol gait-scoring scale was developed to quantify broilers’ ability to walk. The scale is from 0 to 5. If a broiler has a completely normal gait it receives a gait score (GS) 0 and if it cannot walk it is appointed GS5. Until now, most attention has been paid to broilers with GS3 or more, i.e. boilers that are at least noticeably lame, whereby their ability to manoeuver and accelerate is affected. 

A survey of walking ability in Danish broilers in 2011 showed that the proportion of broilers with GS2 was 83 percent – an increase from 34 percent in 2004/2005. The latest study from 2016/2017, however, shows that the proportion of broilers with GS2 is reduced but still high (31 percent). Broilers with GS2 have a definite and identifiable defect in their gait but it does not hinder them from moving or competing for resources. It is this group of broilers that the researchers are presently investigating.   

- Knowledge about the causes of GS2 and how it may affect the health and welfare of broilers is lacking. Considering the proportion of broilers in Denmark and abroad with GS2, it is important to generate knowledge about the issue, says Senior Researcher Anja Brinch Riber from the Department of Animal Science at Aarhus University. 

What does impaired walking ability mean to the broiler?

To generate more knowledge about possible correlations between GS2 and, for example, leg health, pain and body conformation, broilers with GS2 are compared with broilers with a normal gait (GS0). 

- The aim is to identify factors that are important for the occurrence of GS2 in broilers, Anja Brinch Riber explains.   

The study includes 192 experimental broilers.   The intensive data collection period lasts from the broilers are approximately 27 days old to 38 days. Half of the experimental broilers have GS2 while the other half are broilers with a normal gait, i.e. GS0. 

During the first two days of the trials, the broilers will be monitored by video to study their undisturbed behaviour, body postures and their activity level. One day, they will be administered an analgesic. After these first two days, the broilers will go through several tests. 

The first test is a runway with obstacles. This consists of a starting box, an area with obstacles, and a goal area made more attractive by the presence of other broilers and  mealworms. The aim of this test is to investigate if broilers with impaired walking ability spend more time reaching the goal area than broilers with a normal gait. Half of the experimental broilers will be administered an analgesic before the test. 

After the test in the runway, the broilers are subjected  to a conditioned place preference test. This test is used to evaluate emotional states such as pain in animals. For the first time, this test has been adapted for use in broilers, and the researchers will investigate if broilers with impaired walking ability experience a positive emotional state when they are treated with an analgesic. 

- We hope we can use this test to acquire new knowledge about possible emotional states connected to GS2 – in particular if this level of gait characteristics is related to pain, says Anja Brinch Riber. 

Ultimately, the broilers will be euthanised and a range of measurements for disease and health will be investigated, with a focus on leg abnormalities. The researchers will also investigate body conformation, in particular because the large breast seen in broilers is considered important for gait characteristics.    

The study is being carried out as part of the agreement between Aarhus University and the Ministry of Environment and Food of Denmark regarding policy support and in collaboration with researchers Jo Murrell from Bristol University and Dale Sandercock from Scotland’s Rural College. 

For more information please contact:

Senior Researcher Anja Brinch Riber, Department of Animal Science, email: anja.riber@anis.au.dk, telephone: +45 8715 7949 

Senior Researcher Mette S. Herskin, Department of Animal Science, email: mettes.herskin@anis.au.dk, telephone: +45 87157945, mobile: +45 5050 2969