Rearing pullets for aviaries brings bone benefits

Of all the aspects researchers are evaluating to help laying hens adapt to alternative housing, very little is known about the effect of aviary rearing systems on bone health. A collaboration between human and poultry researchers is now applying state-of-the-art technology to another piece of the puzzle to give producers usable insights into open housing designs and decisions. 

Dr. Bettina Willie is a professor in the Faculty of Dental Medicine and Oral Health Sciences at McGill University in Montreal, and joined the university in 2015. She’s a bioengineer with a lab at the Shriners Hospitals for Children-Canada where she uses high resolution imaging to study bone fragility in young children. 

“I became interested in laying hens as a relevant animal model for my work in children because hens are the most efficient land animal at being able to move calcium from their bones to daily egg shell production,” Willie says. “I knew the findings in chickens will be highly transferrable to human health.”

When Willie looked for poultry researchers to collaborate with, she connected with Dr. Tina Widowski, professor in Animal Biosciences and Egg Farmers of Canada Chair in Poultry Welfare at the University of Guelph. Willie joined Widowski’s multi-disciplinary research project looking at the impact of aviary rearing on various aspects of pullets, including behaviour and physiology. Willie and a McGill colleague Dr. Svetlana Komarova brought their expertise in human bone research to the poultry project. 

A bone health baseline
“Bones constantly adapt to maintain their strength and integrity to support different daily activities,” Willie says. “We investigated how rearing birds in different styles of commercially available aviaries affects bone health and structure in white- and brown-feather pullets.”

Willie and her PhD graduate student Isabela Vitienes conducted two research projects using state-of-the-art 3D imaging and equipment – that has never been used in poultry research – to examine the bone’s response to mechanical stimuli. 

They started by determining if the bones of white- and brown-feathered pullets differ depending on the style of aviary they are reared in, to provide baseline information of bone health. 

The scientists raised the pullets at the University of Guelph’s Arkell Research Station in three aviary styles, representing commercially available systems that provide varying levels, perches and ramps for birds to move about in. 

They completed evaluations on bone health at 16 weeks of age after birds had time to adapt to the different environments.

To measure a baseline of bone health, Vitienes inserted sensors onto the leg bones of pullets to measure the birds’ bone mechanics. 

Sensors tracked the amount of strain put on the leg bone during normal daily activities in the rearing environments – walking, running, perching, jumping, etc. 

“One of the things we looked at was which activities best stimulate the bird to build bone mass,” Vitienes says. “We wanted to determine, for example, if birds need more vertical or horizontal space to get the level of physical stimuli they need for healthy bone formation.”

The depth of detail – including bone thickness, volume and curvature – provides indicators of fracture risk and overall bone health that affect the long-term health and wellness of laying hens. 

Whites win again
What they found wasn’t entirely unexpected. Compared to conventional cages, aviary rearing improved the bone structure of white-feathered birds, but not brown feathered. 

“We have seen similar results in several parts of this projects,” Widowski says. “We know that white-feathered birds benefit the most from the complexity of aviaries because they are the only ones that use the space. And we saw that in the improved bone structure.”

The brown-feathered birds don’t benefit because they aren’t using the space. “It’s like giving people access to a gym – the only ones that benefit are those that use it,” Widowski says.

Any aviary style is a plus
When Willie and Vitienes looked for differences in bone structure between the aviary styles, they didn’t find any significant differences. “We see that aviary rearing improves bone compared to conventional cages, but there was no difference between the different style of aviaries,” Willie explains. 

“Thus, the level of complexity does not appear to be important for bone health, since all three aviaries we examined reached the necessary threshold of providing access to bone-stimulating activities.” 

This also jives with what Widowski sees in other aspects of aviary rearing – any style of aviary will benefit birds compared to conventional cages. 

Will workouts build bone strength?
The second project involved applying a mechanical load to one of the pullet’s leg bones. This artificial activity – performed for a few minutes, five days a week over a two-week period – was intended to represent more activity than the baseline measured in the first project. They were seeing how the bone responds to mechanical loading by giving the birds a workout to see if that extra activity might change/improve bone structure. 

While the results aren’t in yet, Willie and Vitienes will be using micro CT imaging to compare the two leg bones – the one that got the added workout, and the one without – to see if there are differences in the bird’s ability to build bone based on the environment they are raised in, as well as genetic strain differences. 

“We are hoping to be able to report which feather colour and aviary rearing style results in birds that better respond to access to exercise with stronger bones,” says Willie.

Building a whole bird picture
“Bone health is so important for bird welfare,” says Widowski, who recognized the unique opportunity to pair her poultry research knowledge with Willie and Komarova. “Being able to collaborate with human bone experts, and the sophistication of their facilities and equipment, is helping build a much more complete picture about what’s important in aviary rearing for the overall health and wellbeing of pullets.”  

This research is funded by the Canadian Poultry Research Council as part of the Poultry Science Cluster, which is supported by Agriculture and Agri-Food Canada as part of the Canadian Agricultural Partnership, a federal-provincial-territorial initiative.