By Yara Raad
Exercise during development can have dramatic effects on the shape, form and strength of bones. Hens reared in aviaries, with opportunities for a variety of load-bearing exercise, develop larger keel bones and experience fewer fractures throughout adulthood in comparison to hens reared in conventional cages. We hypothesized a positive relationship between wing-assisted incline running (WAIR), a load-bearing locomotive behaviour often performed in rearing aviaries, and keel bone development. Our objective was to directly test the effect of a standardized exercise regime employing wing-assisted incline running (WAIR) during rearing on the lateral keel bone size. Fifteen Dekalb White and 15 Hyline Brown laying pullets were exercised twice/week on a 60°-65°ramp from 5 to 21 weeks of age.. Pullets were required to complete a minimum of 10 runs on the ramp and continue the exercise until two runs with a 40% decrease in velocity was seen. A control group (n=15 per strain) was not exercised but was housed in identical floor pens. At 40 weeks of age, hens were humanely killed, keels were dissected, cleaned, and photographed. Digital images were traced and the lateral keel area was calculated using ImageJ with observer blind to treatment. The lateral keel area was corrected for bodyweight (mm2/kg) and analyzed using the Glimmix procedure in SAS. Contrary to our expectations, exercised laying hens had proportionally smaller lateral keel areas (F=7.77,df=1,48,P=0.0076). This leads us to conclude that WAIR is not the behaviour responsible for the increase in keel bone size observed in aviary-reared hens. Therefore, it is possible that WAIR-exercised birds used their leg muscles more than their wings for aerial transitions in the home pen. Future research should measure pectoralis force acting on the keel during different styles of flapping in the home pen.
