Egg output higher in lower-density enriched colonies
Research with white layers shows a slight improvement in egg production for hens provided 116 square inches or more of space in enriched colony cages.
Enriched colony cages for laying hens have been developed as an alternative to battery cages, which were banned in the EU in 2012. The United Egg Producers (UEP) and the Humane Society of the United States (HSUS) forged a hen welfare agreement that called for a transition out of battery cages over an 18 year period. The standard housing density for white hens in enriched colony housing in the EU is 116 square inches per bird. The UEP and HSUS agreement, which has now expired, called for white hens to be housed at 124 square inches per bird in enriched colonies. The 124 square inch standard was arrived at as a result of negotiation and was not based on research results.
Michigan State University conducted a study where white Hyline W-36 hens were housed in enriched colonies at varying densities and egg production, feed intake, bird health and hen well-being measurements were collected. The bird well-being measures were of health, stress and behavior.
Egg production data
The space allotments per hen in the study treatments were 72 square inches (464 square centimeters), 90 square inches (580 square centimeters), 101 square inches (651 square centimeters), 116 square inches (748 square centimeters), 124 square inches (799 square centimeters), and 144 square inches (929 square centimeters). The number of hens housed per enclosure was varied to obtain the housing densities tested in this study, so the group size varied as well as the housing density. Data was recorded for the hens from 17 to 69 weeks of age. Production measures including egg production, body weight, egg weight and feed disappearance were collected.
Hen-day production was similar across all housing densities. Hens with greater than 116 square inches (748 square centimeters) of space per hen had slightly higher production compared to hens with less space allowance. Egg production declined over time with all treatments ending around 79 percent, with the exception of the 144 square inch (929 square centimeter) treatment which ended around 82 percent. Egg weight, feed consumption and body weights were similar across all treatments.
The other aspect of the trial was to evaluate the health, stress and behavior of the birds using the European Union Welfare Quality (WQ) Assessment Protocol for Poultry (Welfare Quality Consortium, 2009). The Avoidance Distance Test, which assesses the hen's response to humans, was not practical as the hens interacted with farm staff daily during egg collection and were habituated to human presence. The fear response of the hen was therefore only assessed using the Novel Object Test. The hen's responses to the novel object, a colorful rod, were not different by density.
According to the WQ protocol hen health can be assessed through observation of hens with labored breathing/sneezing and visual examination of feces to identify enteric infections. Based on these procedures, hen health was deemed not to be of issue. The lack of health concerns was confirmed by an avian pathologist who conducted necropsies of mortality. Due to lower than expected numbers of pullets at placement, the sacrificing of pullets was not possible, and the adrenal weights of the pullets, an indicator of stress, were not evaluated.
The welfare quality measures of comb abnormality, comb wound, keel deformation or fracture, skin lesions, toe damage, foot condition, and plumage damage were assessed bi-monthly in 10 percent of each enriched colony population. Keel deformation or fracture increased over time and was similar amongst all treatments over time (20 to 30 percent). The plumage damage was assessed on seven different areas of the hen. All areas became worse with time (increased feather loss or feather breakage), and the areas of the head, abdomen, and back were impacted by density with the proportion of hens having worse plumage quality housed at 72 square inches (464 square centimeters).
The researchers suggest that additional studies should focus on finding the density between 101 square inches (651 square centimeters) and 116 square inches (748 square centimeters) at which improvements to feathering occurs.