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To measure the activity levels of the broilers, the researchers fitted them with a non-invasive Fitbit-like device, which they strapped around their wings like a backpack. They placed a four-inch-high beam in the middle of the pens for a period of five hours, during which time they counted the number of times the chickens crossed the beam while traveling between their food and water.
“This test has been validated against traditional gait scoring systems to determine lameness in chickens: the more lame the birds, the less they cross,” says Torrey. “We have found that the number of level crossings is decreasing as growth rates are increasing. Compared to the slower growing strains, the conventional strains crossed about four times less. “
In addition to identifying differences in mobility and activity levels, the researchers found higher cases of foot damage and muscle myopathy (meat defects) in faster growing broilers.
Slower growing genetics are being promoted in specialty markets, Widowski says, and there is a tendency to use them in Europe. In countries like Germany, the Netherlands and France, Torrey explains, slow-growing broilers could take an additional 20 to 50 days to reach the same weight in the market. This additional delay has implications for producers – because of the cost of feeding and housing the animals for a longer period – and for consumers in terms of the higher cost.
“We were looking for strains that might be viable in the North American market, where consumers also appreciate the yield and price of the breasts,” says Torrey. “We have had birds that took a week or two longer to reach the same body weight as the conventional strains used. And there were some that took a week longer and performed well in terms of social outcomes. But overall, growth rate and breast performance are related to most of the wellness outcomes we looked at: the faster the growth, the poorer the outcome.