Animal Welfare: Do Piglets in Pens Go Hog Wild for Certain Colors?
Featured Image Caption: Pig farm Vampula by kallerna CC by SA 4.0 via Wikimedia Commons
Primary Source Article: Götz, S., Reiter, K., Wensch-Dorendorf, M., von Borell, E., & Raoult, C. M. C. (2025). Role of Illumination and Light Colour Temperature in the Preference Behaviour of Weaned Piglets. Animals, 15(21), 3116. https://www.mdpi.com/2076-2615/15/21/3116
Secondary Source Article: Sossidou, E. N., Banias, G. F., Batsioula, M., Termatzidou, S.-A., Simitzis, P., Patsios, S. I., & Broom, D. M. (2025). Modern Pig Production: Aspects of Animal Welfare, Sustainability and Circular Bioeconomy. Sustainability, 17(11), 5184. https://doi.org/10.3390/su17115184
According to the U.S. Department of Agriculture (USDA), the U.S. hog industry has experienced significant structural changes in the last 40 years, namely shifting to fewer but larger operations. As the density of pigs in farming increases, so does the need to ensure the animals’ welfare. Most people would think that these considerations are only limited to air, water, waste management, and health. However, researchers from Germany wanted to look at a different aspect of animal welfare by studying a variable that has been overlooked in most pen designs: lighting.
Light plays an important role in regulating the biological processes of both animals and plants. It is a factor that signals when to wake, sleep, migrate, and reproduce. Therefore, these researchers conducted a pilot study to determine if pigs can distinguish between different lighting and if they have a preference for a specific lighting condition.
To test whether piglets had this preference, researchers designed four pen compartments in which the piglets could roam freely. Two pens were permanently dark, one pen had yellow warm white lighting, and the last pen was set to cool blue lighting. Over the course of 5 weeks, the animals were monitored and pen preference was evaluated based on how soiled a room was (indicating use), feeding patterns, behavioral patterns, and time spent in each pen. Behavioral patterns were evaluated using a video camera to determine whether piglets were lying, feeding, drinking, moving, or active. Cleanliness was scored from 0-4 from no soiling to heavily soiled.
Overall, the only pattern that researchers could surmise is that the piglets’ movement within compartments was based on the time of day. Pigs were observed to be most active between 6am and 4pm and resting in the evening from 8pm to 4am. Piglets spent most of their time in the pens with yellowish light, then later preferred the dark pens during the last experimental week. However, the pen that was in the cool blue range was where pigs were most active.
So, Where Do Piglet’s Stand in Light Preference?
During the 5-week experiment, researchers concluded that the pigs did not have a fixed preference for any particular lighting condition. Instead, they found that the behaviors that they were observing had more to do with their developmental state and their natural circadian rhythm. For the first two weeks, they preferred continuous yellow lighting, but as the weeks progressed, they preferred darker pens. Lighting influenced pen cleanliness, meaning that pigs preferred to keep dark rooms where they slept clean while preferring to soil the rooms with bluish tint.
In spite of the study combining statistical analysis with qualitative observations, researchers admit that there were limitations to the pilot study. The precise age of the pigs, presumably 4 weeks old, was something they could not definitively verify. However, all of the pigs were the same age. External noises, such as voices from the outside test room, were difficult to control. Researchers tried to compensate for noise by choosing test days that were the quietest to study pig behavior. In addition, pigs that were transported had already been exposed to farrowing crates, pens that prevent a mother from crushing her newborn piglets, but restrict natural behaviors. Still, in spite of these differences, this research is an important step towards tackling a simple but important question about lighting conditions and animal welfare.
Why Care if my Bacon is Happy?
Hog welfare is a multifaceted issue that ranges from housing conditions, nutrition, hygiene, and the opportunity for normal biological functioning and behavior display. One of the primary welfare concerns is centered around intensive confinement systems. As of 2025, the U.S. still has a long way to go in terms of balancing hog welfare with economic pressures. Although the economic reasoning for making confined spaces to accommodate more livestock feels sound, the downstream effects of trying to maximize space can pose a biosecurity risk. There is an increased vulnerability for diseases to spread and sanitation standards are more difficult to maintain. In addition, pigs are social animals and certain confinement systems prevent natural behavior and social interaction. This can cause psychological distress that manifests as repetitively biting the cage bars and chewing when no food is present. (bar biting and sham chewing)
Although the study did not find a fixed preference for a specific lighting condition, they observed piglets adjusting their behavior according to the specific light they were exposed to.
In the debate of animal welfare and the farming industry, could design and function go hand in hand with welfare? For example, designing pens with different lighting conditions could potentially encourage pigs to soil certain compartments, making the retrieval of pig manure and sanitation of compartments easier. These findings and approach, along with future studies, could perhaps help design pens that encourage the animal’s natural behaviors that increase the well-being of the animal and benefit the hog industry.
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