Effects of Rearing Aviary Style and Genetic Strain on the Locomotion and Musculoskeletal Characteristics of Layer Pullets

SIMPLE SUMMARY: Consumer trends have led to the popularisation of eggs from hens housed in non-cage systems. Aviaries are common non-cage systems that consist of multi-tiered structures with essential resources located within. Being a ground-dwelling species, laying hens must learn when they are young to navigate aviaries, and develop the strength to do so. However, there are different styles of aviaries with varying degrees of structural complexity in which young laying hens (pullets) are reared. This study examined the differences in locomotion and musculoskeletal characteristics of white- and brown-feathered strains of pullets housed in three different styles of rearing aviaries (low, moderate, and high structural complexity) on commercial farms. Pullets in the most complex system spent the most time locomoting, and white-feathered strains in the highly complex systems performed the most jumps and flights. While there were no differences in muscle weights between aviary styles, white-feathered strains, and pullets in the most complex aviary had stronger leg bones than brown-feathered strains and pullets in the least complex system. These results indicate that the style of the aviary in which pullets are reared can affect their bone strength, most likely through differences in the load-bearing exercises performed. ABSTRACT: Previous research indicates that the musculoskeletal development of pullets is improved when pullets are reared in aviaries compared to conventional rearing cages. However, there are considerable differences in rearing aviary design. To measure locomotion and musculoskeletal development of brown (n = 7) and white-feathered (n = 8) strains of pullets, 15 commercial flocks in three styles of rearing aviaries differing in structural complexity (n = 5 per style) were visited three times: 25.9 ± 6.67, 68.0 ± 4.78, and 112.1 ± 3.34 days of age. Locomotion (duration of standing, sitting, walking, running, flying, and rates jumping, flying, group running and walking) was analysed from videos recorded three times per day: at the beginning, middle, and end of the light cycle. Pullets for dissection were taken on visits 2 and 3. Pullets in the most complex system (style 3; S3) spent the most time locomoting throughout rearing (p < 0.05). Pullets in S3, particularly white-feathered strains, performed the highest rate of vertical transitions (p < 0.05). There were no differences in any of the proportional muscle weights between aviaries styles (p > 0.05) despite the differences in locomotion. White-feathered strains, however, had proportionally heavier pectoralis major (p < 0.0001), pectoralis minor (p < 0.0001), and lighter leg muscles (p < 0.0001) than brown-feathered strains. White-feathered strains and pullets in S3 also had proportionally stronger tibiae and femurs than brown-feathered strains and pullets housed in the least structurally complex system (style 1; S1) (p < 0.05). However, there were no differences found in the breaking strength of the radius and humerus between strain colours or aviary styles (p < 0.05). Therefore, strain, as well as differences in rearing aviary design, can affect the types of locomotion that growing pullets perform, which may, in turn, impact their skeletal development.