Body weight sub-populations are associated with significant different welfare, health and egg production status in Australian commercial free-range laying hens in an aviary system

Abstract

In order to assess the welfare and health status of commercial free-range laying hens of different body weight quantiles, a total of 7708 Lohmann Brown-classic hens at 74 weeks of age were obtained from 4 commercial free-range flocks housed on the same Australian farm under the same housing conditions. All hens were humanely killed and evaluated for body weight, feather cover, keel bone damage, gastrointestinal parasites, liver appearance, and egg follicle status. Hens were classified according to their body weight distribution percentile as light (bottom quartile, 1.65 ± 0.002 kg), medium (middle quartiles, 1.86 ± 0.010 kg), and heavy (top quartile, 2.08 ± 0.002 kg). All parameters were analysed using nominal regression models with flock, body weight, and their interactions as the predictors. In summary, 55.8% of heavy hens had a single or multiple keel bone damage compared to 48.9% and 50.7% of medium and light hens, respectively (P = 0.0001). Light hens had a significantly (P = 0.001) higher feather cover score on their breast (3.02 ± 0.018) than medium (2.96 ± 0.013) and heavy hens (2.87 ± 0.018) but significantly lower neck feather scores (P = 0.007). Light hens had the highest prevalence of gastrointestinal helminth infection (P = 0.0001), compared to the medium and heavy hens. Heavy hens had the highest incidence of Fatty Liver Syndrome compared to medium and light hens. Heavy and medium hens were significantly (P = 0.0001), more often in full egg follicle production (95.3% and 94.8%, respectively) compared to the lighter hens (90.0%). There was a significant flock effect for all parameters investigated. In conclusion, heavy (2.06 ± 0.010 kg) and medium (1.85 ± 0.010 kg) hens appeared healthier, more resilient towards infectious diseases and persistent in their egg follicle production. However, heavier hens suffered significantly more often from Fatty Liver Syndrome. Hens in the lowest quartile with mean 1.65 kg were the least economic sub-population.