Computational modeling used to provide hens better living conditions

Proper ventilation in cage-free hen houses is an important concern for animal comfort, according to a new study. 

The study, which employed computational fluid dynamics, examined four alternative ventilation schemes in a large hen house to assess bird comfort in cold and hot weather conditions in a typical layer house.

Using simplified bird shapes, the study modeled 2,365 individual hens with an approximate body weight of 1.6 kilograms (3.5 pounds) and examined their comfort levels as to temperature, air velocity, and pressure at various locations of the hen house. 

According to the authors, “the ventilation rates of the hen house within the four ventilation schemes fell at the higher end of the desired ventilation range, indicating that the barn could be expected to maintain good air quality during cold weather.” 

The report, by a team of engineers and veterinary specialists at Penn State University and the Tianjin Academy of Agricultural Sciences in China, was published Aug. 8 in the online journal, Animals.

Using computational fluid dynamics (CFD), the group developed four separate three-dimensional models “based on a full-scale, floor-raised layer house.” Each of the four models was based on a variation of the ventilation scheme for the house: 

• The standard top-wall inlet with sidewall exhaust (TISE)

• Mid-wall inlet with ceiling exhaust (MICE)

• Mid-wall inlet with ridge exhaust (MIRE) 

• Mid-wall inlet with attic exhaust (MIAE)

The hen house used for the model was a “typical floor-raised housing configuration,” in Lititz, Pennsylvania. It was 532 feet long by 45 feet wide with a 9-foot tall side wall. Modelers used a one-eighth cross-section of this configuration to model air flow. 

Cage-free vs. battery cage 

The authors note that egg producers’ “uncertainty regarding cage-free housing guidelines” was a prime motivation for their study. 

The designation “cage-free” means that the hens are not confined to long rows of group cages, known as battery cages, in which hens are so tightly packed that they cannot spread their wings. Cage-free hens are able to fly down from the roosting level to a common area, to walk, spread their wings, perch on a steel bar, and lay their eggs in nests. 

However, cage-free hens never go outside, and are usually very densely packed inside the hen houses, conditions that sometimes result in fights and maiming of the birds. In the standard, cage-free layer house used for this model, nearly 20,000 hens were typically housed in the barn at a density of 1.2 square feet per bird. The space per bird amounts to less than that taken up by two sheets of standard 8 1/2 by 11-inch copy paper laid side by side. 

In the European Union and United Kingdom, battery cages have been banned altogether for some years, while in the United States they are still permitted. However, many U.S. food producers have adopted cage-free standards, and cage-free housing is expected to eventually become the norm. The U.S. Department of Agriculture estimated as of 2019, 19.6% of eggs produced for consumption came from cage-free hens. 

Long Chen,et al. Computational Fluid Dynamics Analysis of Alternative Ventilation Schemes in Cage-Free Poultry Housing, Animals (2021). 

DOI: https://doi.org/10.3390/ani11082352