The welfare of broiler chickens part 1: impact of growth rate

Published: April 3, 2023

By: Alexandra Ulans, Virginia Tech; Dr. Leonie Jacobs, Virginia Tech. Reviewers: Prafulla Regmi, University of Georgia; Dr. Shawna Weimer, University of Arkansas; Dr. Marisa Erasmus, Purdue University.

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American and European companies are pledging to move to include slow-growing broiler chickens for production, which means they will use broiler chickens with less efficient growth rates in their production systems. Slow-growing strains show improved welfare outcomes compared to conventional ones.

This newsletter describes some characteristics of fast- and slow-growing broilers, along with the impacts that the differing growth rates can have on the birds’ health and behavior.

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What are fast- and slow-growing chickens?

A fast-growing broiler chicken is a type of chicken that gains weight rapidly and is typically used in commercial broiler chicken farms.

Fast-growing broilers can reach a growth rate of up to 3.5 oz (100 g) per day.

“Slow-growing” broilers have been defined as birds that require an increased number of days to grow to the same size and weight compared to conventional fast-growing strains (NCC, 2016).

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The threshold for average growth per day for strains to be considered slow-growing differs among stakeholders but a commonly mentioned threshold for average daily gain is < 50 g/day over their life span (G.A.P., 2016; Rayner et al., 2020).

Why is growth rate important?

Having a fast growth rate can cause a variety of health concerns for chickens, resulting in discomfort, pain, or even death.

These health concerns tend to mainly impact the cardiovascular and musculoskeletal systems (heart, muscles and bones) of the birds. In addition, the rapid weight gain can change their behaviors as movement becomes more strenuous when birds gain weight (Bokkers, 2004).

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Fast-growing broilers are the most common type of broiler used today, because they are cost-efficient in producing meat. However, consumer concern for animal welfare continues to grow, resulting in an increased use of slower growing breeds (Alonso et al., 2020).

Growth rate impacts health

Fast-growing broilers can be prone to a range of diseases that are associated with their growth rate and/or body weight. Here are some examples.

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By reducing the speed at which broilers grow, the incidences of these health issues decrease significantly (Wideman et al., 2013; Alves et al., 2016; Hartcher and Lum, 2020; Weimer et al., 2020).

Growth rate impacts behavior

Since fast-growing broilers gain weight quickly, their behavioral repertoire changes in comparison to other chicken strains and to when they are younger.

These broilers will spend more time sitting, feeding, and drinking rather than performing behaviors like walking, foraging (searching food), preening (plumage maintenance), dust bathing, perching, and playing (Dixon, 2020; Rayner et al., 2020).

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Due to a variety of factors, fast-growing broilers’ legs tend to become weaker. In turn, long durations of resting on poor-quality litter can result in skin lesions (Hartcher and Lum, 2020).

Slow-growing broilers show more high-energy behaviors, including standing, walking, foraging, and comfort behaviors compared to fast-growing broilers, which suggests improved health and ability to perform normal behavior (Abeyesinghe et al., 2021; Dixon, 2020; Rayner et al., 2020).

Summary: fast- vs slow-growing broilers

Fast-growing broilers have been genetically selected for very efficient growth and muscle development, but are prone to issues with their health and behavior. One way to address these is to use slower-growing strains for meat production instead. This way, chickens are able to adapt to the weight they gain, resulting in less disease and more active birds. However, these birds are less efficient and production will be more costly.

To read part two, click here.

This article was originally published on Poultry Extension Collaborative (PEC) and it is reproduced here with permission from the authors.

References

Sources and additional resources

Abeyesinghe, S. M., et al (2021). Associations between behaviour and health outcomes in conventional and slow-growing breeds of broiler chicken. Animal, 15(7). doi:10.1016/j.animal.2021.100261

Alonso, M. E., González-Montaña, J. R., & Lomillos, J. M. (2020). Consumers’ concerns and perceptions of farm animal welfare. Animals, 10(3), 385. https://doi.org/10.3390/ani10030385

Alves, M. C. F., et al (2016). Locomotion of commercial broilers and indigenous chickens. Brazilian Journal of Animal Sciences, 45, 372-379.

Berg, C. (1998). Foot-pad dermatitis in broilers and turkeys. Swedish University of Agricultural Sciences.

Bessei, W. (2006). Welfare of broilers: a review. World’s Poultry Science Journal, 62(03), 455. doi:10.1017/s0043933906001085

Bokkers, E. A. (2004). Behavioural motivations and abilities in broilers. Wageningen University and Research.

Bradshaw, R. H., et al. 2002. “A Review of the Aetiology and Pathology of Leg Weakness in Broilers in Relation to Welfare.” Avian and Poultry Biology Reviews 13: 45–103. doi:10.3184/147020602783698421

Closter, A. M., et al (2012). Genetic correlation between heart ratio and body weight as a function of ascites frequency in broilers split up into sex and health status. Poultry science, 91(3), 556-564.

Crespo, R., & Shivaprasad, H. L. (2013). Developmental, metabolic, and other noninfectious disorders. Diseases of poultry, 1233-1270.

Dinev, I., Denev, S., Vashin, I., Kanakov, D., & Rusenova, N. (2019). Pathomorphological investigations on the prevalence of contact dermatitis lesions in broiler chickens. Journal of Applied Animal Research, 47(1), 129-134.

ELANCO. (2016). The Sustainability Impacts of Slow-Growing Broiler Production in the US.

G.A.P. (2016). Our Commitment to Improving Bird Welfare with 100% Slower-Growing Chicken Breeds.

Hartcher, K. M., & Lum, H. K. (2020). Genetic selection of broilers and welfare consequences: a review. World’s Poultry Science Journal, 76(1), 154–167. doi:10.1080/00439339.2019.1680025

Kalichman, L., et al (2009). Spondylolysis and spondylolisthesis: prevalence and association with low back pain in the adult community-based population. Spine, 34(2), 199.

Kelly, W. R. (1971). Occurrence of spondylolisthesis (kinky-back) in broiler chickens in South Australia. Austral. Vet. Journal.

Makrai, L., et al. (2011). Association of Enterococcus cecorum with vertebral osteomyelitis and spondylolisthesis in broiler parent chicks. Acta Veterinaria Hungarica, 59(1), 11-21.

National Chicken Council (NCC). (2016). The sustainability impacts of slow-growing broiler production in the US.

Rayner, A. C., et al (2020). Slow-growing broilers are healthier and express more behavioural indicators of positive welfare. Scientific Reports, 10, 15151. doi:10.1038/s41598-020-72198-x

Weimer, S. L., et al (2020). Differences in performance, body conformation, and welfare of conventional and slow-growing broiler chickens raised at 2 stocking densities. Poultry Science, 99(9), 4398-4407.

Wideman, R. F., et al. (2013) Susceptibility of 4 Commercial Broiler Crosses to Lameness Attributable to Bacterial Chondronecrosis with Osteomyelitis. Poultry Science 92: 2311–2325.

Wijesurendra, D. S., et al (2017) Pathological and Microbiological Investigations into Cases of Bacterial Chondronecrosis and Osteomyelitis in Broiler Poultry. Avian Pathology 46 (6): 683–694.

Wilson, F. D., et al (2020). A Field Study of Histologic and Bacteriologic Characterization of Femoral Head Separation and Femoral Head Necrosis. Avian Diseases, 64(4), 571-581.

The welfare of broiler chickens part 1: impact of growth rate

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