Building a better laying hen
How early life experience affects behaviour, health, and welfare
By Ana Rentsch and Tina Widowski
The mandates for cage-free housing pose challenges for North American egg producers and their birds. This is especially true for laying hens housed in complex multi-tiered aviaries where the birds must be able to find nests, food, and water that are often located on different levels. In these spatially complex and often crowded environments, hens must also be able to perch, jump, land, and balance without falls or collisions. Furthermore, excessive fear reactions can lead to injury through collisions or piling events. In short, to survive and thrive in a complex housing system, hens must be smart, calm, and physically fit.
When laying hens were primarily kept in conventional battery cages, they could also be reared in similarly barren cages where they had just enough room to eat, grow and prepare for egg production. Not much was known, or needed to be known, about the laying hen's behavioural or physical development. By now, it is clear from both practical experience and scientific research that hens destined to be housed in aviaries must be reared in similarly complex environments, as this experience during development enhances spatial cognitive abilities, use of 3-D space, and reduces fearfulness (Campbell et al, 2019). There is also evidence for a sensitive period during the first few weeks of a chick's life where certain skills must be learned or there will be long-term deficits. For example, hens that do not learn to perch before they eight weeks of age will have inferior perching skills for the rest of their lives. In addition to perching, rearing in complex environments with a variety of structural elements such as ramps, terraces and perches of different heights improves the skills needed for ascending, descending, balancing, and way-finding (Norman et al. 2021).
Another benefit of rearing pullets in complex aviary housing is improved bone strength due to exercise. Bones have sensory receptors that respond to mechanical strains from the muscles anchored to them and to mechanical loading from load bearing activites - for example, ground reaction forces from high impact jumps. When these mechanical forces are detected, osteocytes respond by remodelling bones which changes their shape and thickness to impart greater strength where needed. Bones are especially sensitive to exercise before puberty when the skeleton is still developing, meaning that opportunity for exercise during rearing can enhance the bone mass of young laying hens before they even lay their first egg. Strong bones are particularly important for laying hens as they lay daily eggs requiring just over two grams of calcium for the eggshell, and lying hens use bone as a source of calcium. Therefore, it is not surprising that many laying hens suffer from osteoporosis (weak bones), making them prone to bone fractures. A bone that is particularly prone to fracture is the keel (sternum). Several years ago, a large, longitudinal study in the laboratory of Tina Widowski at the University of Guelph in Ontario Canada demonstrated that rearing pullets in an open concept aviary in which birds could run, jump and fly from 1 day of age led to larger and stronger bones, including the keel (Casey-Trott et al, 2017a,b) and fewer keel fractures (Casey-Trott et al., 2017c) compared to rearing in conventional cages.
However, not all rearing aviaries are designed the same. There are several typical designs of commercial rearing aviaries on the market. The main difference between the different types is the design of the brooding compartment, where chicks are confined for the first few weeks of life to make them more manageable. Based on the brooding compartment designs, rearing aviaries can be categorized into aviaries of low (Low), medium (Mid), and high (High) complexity. The brooding compartments of the Low-complexity aviary consist of cages with one or two low perches, depending on the manufacturer. The brooding compartments in the low complexity aviaries are most similar to conventional rearing until the systems are opened. Mid-complexity aviaries have larger brooding compartments that include more and higher perches and an elevated platform to add additional vertical complexity. In High-complexity aviaries, like the open-concept model in our earlier study, chicks are not confined to cages at all during brooding but rather have the run of the barn from day one with a greater number of perches than in Mid and an elevated platform for vertical complexity. After brooding, the sytems are opened in all types of aviaries and pullets gain access to the rest of the barn, including a litter area, multiple levels, multiple perches, and occasional ramps. The considerable variation in brooding compartment design and complexity raised the question of whether birds behave and exercise differently in these different types of commercial avieiries and if there are any effects on behaviour, bone or muscle development.
In a field study including 15 pullet flocks on 11 commercial farms in two Canadian provinces, former Master student Amanda Pufall collected videos at three time-points (Pufall et al., 2021). She found that pullets in the High-complexity aviaries locomoted the most (running, jumping, and flying). Differences were most pronounced during brooding and white-feathered birds performed more aerial behaviour than brown-feathered birds. At the end of rearing, Pufall collected birds for dissections and found that pullets from High had the strongest leg bones, and white birds had proportionally stronger leg bones and larger keel bones and breast muscles than brown birds.
On commercial farms, pullet growers keep chicks in brooding compartments for different amounts of time. In Pufall’s study this ranged from 22 to 91 days with an average of around 5 and a half weeks, depending on system and produce preferences. Additionally, different producers feed different diets and manage their pullets differently. Hence, a controlled study at the research station followed the field trial. The Arkell research station at the University of Guelph has two smaller versions of each of the three commercial rearing aviary types as well as conventional pullet cages. Four flocks of brown and white pullets (reared separately) were raised in each of the systems, and the brooding compartments were opened at exactly six weeks after hatch in all groups. Former Master's student Erin Ross assessed musculoskeletal traits in pullets from the first two flocks at 6, 11 and 16 weeks of age (Ross, 2021). Ross showed that aviary-reared pullets had stronger wing and leg bones, greater muscle weight, and larger keels compared to pullets reared in conventional cages, and the benefits appeared to be broadly realized from aviary rearing and not specific to any particular style. The findings provide futher evidence that aviary rearing has profound effects on the physical development of layer pullets, although white-feathered pullets tended to reap greater benefits for some measures..
Throughout all four flocks, former Ph.D. student Ana Rentsch performed numerous behaviour tests to assess the effect of early environmental complexity on physical and cognitive spatial skills and fear behaviour (Rentsch, 2023). One behaviour test examined how quickly birds learned to find a food reward or an escape route in a T-maze. High and Mid pullets were faster to pass the test than pullets from conventional cages, and white pullets were faster than browns. A method to quantify fearfulness or fear responses is to put birds in an unfamiliar place with unfamiliar objects and measure their responses in a standardized way. Rentsch found conventionally raised pullets to explore less and appear more alert in a novel arena, indicating they were more fearful than aviary-reared pullets. Another spatial test assessed birds' willingness or ability to go up and down from a raised platform (Rentsch et al., 2023b). Birds were encouraged to go up or down using a food reward, and they could jump or use a ramp. Cage-reared birds did poorly in all tasks, especially going up, and did not appear to know how to use a ramp. Pullets from High-complexity aviaries were faster to complete the tasks. Overall, the greatest differences in behaviour were between standard cage- and aviary-reared birds, with fewer differences between the different styles of rearing aviaries. Behavioural observations also showed that white pullets used the system and generally exercised more than browns (Rentsch, et al., 2023a).
Combined years of experiments and the efforts of numerous students, staff, and chickens repeatedly demonstrate that early experience and rearing system complexity profoundly affect the musculoskeletal characteristics and behaviour of laying hen pullets. The different aviary types lead to different types of activities and amounts of locomotion and exercise. Concerning musculoskeletal and behavioural development, major differences were found between conventional cages and aviaries, with only minor differences between aviary types. The brown and white-feathered strains observed in these studies used the systems differently, with white pullets using and benefiting from higher environmental complexity more than brown-feathered pullets.
About the authors
Ana Rentsch earned an MSc studying the behaviour of laying hens with keel fractures at Centre for Proper Housing of Poultry and Rabbits, VPHI at the University of Bern in Switzerland before moving to Guelph for her PhD.
Tina Widowski is Professor of applied animal behaviour and welfare in the Department of Animal Biosciences at the University of Guelph. She holds the Egg Farmers of Canada Research Chair in Poultry Welfare. Widowski also serves on the Scintsits Advisory Committee on Animal Welfare for the United Egg Producers.
View our interview with the researchers from Poultry Science Association annual meeting.
References
Campbell, D.L.M., De Haas, E.N. and Lee, C., 2019. A review of environmental enrichment for laying hens during rearing in relation to their behavioral and physiological development. Poultry Science, 98(1), pp.9-28. https://www.sciencedirect.com/science/article/pii/S0032579119302822
Casey-Trott, T.M., Korver, D.R., Guerin, M.T., Sandilands, V., Torrey, S. and Widowski, T.M., 2017a. Opportunities for exercise during pullet rearing, Part I: Effect on the musculoskeletal characteristics of pullets. Poultry Science, 96(8), pp.2509-2517. https://www.sciencedirect.com/science/article/pii/S0032579119314464
Casey-Trott, T.M., Korver, D.R., Guerin, M.T., Sandilands, V., Torrey, S. and Widowski, T.M., 2017b. Opportunities for exercise during pullet rearing, Part II: Long-term effects on bone characteristics of adult laying hens at the end-of-lay. Poultry Science, 96(8), pp.2518-2527. https://www.sciencedirect.com/science/article/pii/S0032579119314476
Casey-Trott, T.M., Guerin, M.T., Sandilands, V., Torrey, S. and Widowski, T.M., 2017c. Rearing system affects prevalence of keel-bone damage in laying hens: a longitudinal study of four consecutive flocks. Poultry science, 96(7), pp.2029-2039. https://www.sciencedirect.com/science/article/pii/S0032579119313902
Norman, K.I., Weeks, C.A., Tarlton, J.F. and Nicol, C.J., 2021. Rearing experience with ramps improves specific learning and behaviour and welfare on a commercial laying farm. Scientific Reports, 11(1), p.8860. https://www.nature.com/articles/s41598-021-88347-9
Pufall, A., Harlander-Matauschek, A., Hunniford, M. and Widowski, T.M., 2021. Effects of rearing aviary style and genetic strain on the locomotion and musculoskeletal characteristics of layer pullets. Animals, 11(3), p.634. https://www.mdpi.com/2076-2615/11/3/634
Rentsch, A.K., 2023. Raising Laying Hens: The Effect of Early Life Environmental Complexity and Genetic Strain on Behavioural Development, Doctoral dissertation, University of Guelph, https://atrium.lib.uoguelph.ca/xmlui/handle/10214/27422Rentsch, A.K., Harlander, A., Siegford, J., Vitienes, I., WILLIE, B. and Widowski, T.M., 2023a. Rearing laying hens: the effect of aviary design and genetic strain on pullet exercise and perching behavior. Frontiers in Animal Science, 4, p.57. https://doi.org/10.3389/fanim.2023.1176702
Rentsch, A.K., Ross, E., Harlander, A., Niel, L., Siegford, J.M., and Widowski, T.M., 2023b. The development of laying hen locomotion in 3D space is affected by early environmental complexity and genetic strain. Scientific Reports, https://doi.org/10.1038/s41598-023-35956-1
Ross, E., 2021. The Effect of Early Rearing Environment on Musculoskeletal Traits and Proximate Composition in Laying Hen Pullets, Master’s thesis, University of Guelph, https://atrium.lib.uoguelph.ca/xmlui/handle/10214/26363
