Understanding the Differences Between Meat Chickens and Laying Hens

Gadzama, I. U.ᵃ,* and Ray, Sᵇ

ᵃDepartment of Primary Industries and Regional Development, WA 6743 Australia

ᵇOlam Orchards Australia Pty Ltd, Mildura, VIC 3549 Australia

*Corresponding author: [email protected]

Introduction

The modern chicken (Gallus gallus domesticus) has been bred over the years to produce either eggs or meat for human consumption (Eda, 2021). Modern breeding focuses on productivity, with some chickens (layers) being great at laying eggs and others (broilers) being good for meat production (Korver, 2023). Meat chickens and laying hens are all domesticated birds but are bred for different purposes. This means they look and behave differently (ACMF, 2013). Even among meat chickens, there are two types: fast-growing and slow-growing (Figure 1A). Fast-growing meat chickens, such as Ross or Cobb breeds(Figure 1B), are commonly used in Australian free-range commercial farms. In contrast, some European free-range systems use slow-growing breeds due to legislation requiring meat chickens to reach at least 81 days before slaughter (European Commission, 2008). Slow-growing chickens are more active and explore the range area better than fast-growing chickens (Bokkers and Koene, 2003; Zhou et al., 2024). Studies have shown that slow-growing chickens spend more time outside foraging compared to fast-growing strains, which is attributed to genetic differences (Fanatico et al., 2005; Zhou et al., 2024). Fast-growing meat chickens reach slaughter weight at 5 to 6 weeks of age, while slow-growing chickens reach market weight at 12 weeks before they reach sexual maturity (Dixon, 2020).

Figure 1 (A) Slow-growing meat chickens; (B) Fast-growing meat chicken

Adapted from https://www.chickencheck.in/faq/difference-faster-slower-growing-chicken/

Housing Systems for Meat and Layer Chickens

Meat chickens are kept in large barns on deep litter, such as wood shavings, straw, or rice hulls, rather than in cages like conventional laying hens. Layer chickens are primarily raised in cage systems with limited space. These systems can be high-rise (HR), which make up 65-70% of cage systems, or manure-belt (MB), which account for 25-30% (Xin et al., 2010). Alternative cage-free housing systems are also becoming more popular. In HR facilities, manure is stored in the lower level of the house for a year and removed as solid manure in the fall for use on cropland. In MB houses, manure is removed daily to weekly via the manure belt and can be stored on-site, in separate storage, or at a composting facility (Xin et al., 2010). 

Common Bedding Materials for Chickens

Bedding for broiler housing varies by location but commonly includes:

• Sawdust
• wood shavings
• rice, wheat or rye hulls
• chopped straw
• corn stalks
• peanut shells
• paper products
• sand

What is a Litter?

Bedding materials are referred to as litter when mixed with faeces (Figure 2). Most of the litter is reused over multiple flocks. However, caked litter, which has a wet and hardened surface layer usually found along feed and water lines, is removed between each flock.

Figure 2. Broiler chicks in floor pens with fresh bedding (left) and reused litter (right)

Adapted from Oladeinde (2022)

Fresh Litter vs. Reused Litter

Poultry litter, a mix of bedding materials and bird excreta, plays a crucial role in broiler chicken farming. Reusing poultry litter can boost the birds’ immune systems and help prevent the spread of antibiotic resistance between bacteria (Figure 2; Oladeinde, 2022). However, reused litter creates a more complex environment, significantly impacting flock growth and health (Cressman et al., 2010). Reused litter contains more intestinal microbes than fresh litter, which has more environmental bacteria (Cressman et al., 2010).

Fresh litter tends to have more Lactobacillus spp., while reused litter has more Clostridiales bacteria, impacting the small intestine (ileal) microbiota more than the large intestine (cecal) microbiota (Cressman et al., 2010). The influence of fresh litter decreases as broilers grow, whereas reused litter continues to affect the microbiota throughout the rearing period (Cressman et al., 2010). Clumps and caked, wet litter can lead to footpad damage and footpad dermatitis (Tabler et al., 2021). Cressman et al. (2010) examined the effects of fresh pine shavings versus reused litter on the intestinal microbiota of broiler chickens over 6 weeks, showing that fresh litter had more environmental bacteria, while reused litter contained more bacteria from the chickens’ intestines. Fresh-litter chicks had more Lactobacillus spp. in their intestines, whereas reused-litter chicks had more bacteria from the Clostridiales group. The type of litter used can significantly affect the gut health of broiler chickens, with fresh litter having a different impact compared to reused litter. The type of litter had a greater impact on the ileal (small intestine) microbiota than on the cecal (large intestine) microbiota. The influence of fresh litter on the ileal microbiota decreased as the broilers grew, while the reused litter continued to affect the microbiota throughout the rearing period.

Water Activity in Litter and Its Impact on Chicken Health

Litter moisture content is important for assessing litter quality, but water activity (Aw) is even more crucial. Water activity measures the available water in the litter, which affects microbial growth (Dunlop et al., 2016). Maintaining litter below a critical Aw value can reduce the growth of pathogens like Salmonella and E. coli (Tabler et al., 2021).

Growth Rates of Meat Chickens vs. Laying Hens

Meat chickens gain weight much faster than laying hens (Ohta et al., 2004). Although both are descendants of the red jungle fowl, they have been bred for different purposes and have different digestive efficiencies (Jackson & Diamond, 1996; Nguyen‐Phuc & Berres, 2018; Eda, 2021). Meat chickens are selected for fast growth and efficient feed conversion, with about 3 kg of feed producing 2 kg muscle in just 5 weeks (Zuidhof et al., 2014).

Meat chickens consume more feed than layers, and their feed is usually in pelleted form to ensure they get all the necessary nutrients quickly. In contrast, laying hens are small female chickens that consume a small amount of mash feed and produce eggs. Mash feed is given to layers to increase their feeding time and reduce weight gain, as overweight hens produce fewer eggs (Ohta et al., 2004). Although there is no difference in egg weight between meat chickens and laying hens (Ohta et al., 2004), layers are too small to be used for meat production.

Effects of Age and Rearing Systems on Meat Quality

Broiler meat is more tender than laying hens (Figure 3; Fairchild, 2005). Layers are allowed to reach sexual maturity, producing hormones that make their meat tougher. They can live up to 96 weeks before being culled, making their meat stronger and tougher (ACMF, 2013). Meat chickens, on the other hand, grow quickly and have a smaller environmental footprint than other meat types (de Vries and de Boer, 2010). This efficiency has led to a significant increase in meat chicken production, with over 86 million tonnes produced worldwide in 2010 (FAOSTAT, 2012). The study by Semwogerere et al. (2018) looked at the carcass characteristics and meat quality of spent layers (Lohmann Brown-Elite) raised in conventional battery cages and free-range systems. The study showed that caged hens (aged 40 weeks) had heavier warm and cold carcasses, thighs, wings, and feet. They also had higher percentages of breast meat, drumsticks, and breast bones and experienced more breast thaw and cooking loss, as well as thigh cooking loss.

In contrast, the free-range hens (aged 53 weeks) had heavier gizzards and bones but a lower percentage of breast meat. Their meat was redder and had higher skin redness, breast and thigh shear force values (indicating tougher meat), breast moisture, and thigh ash content. They also had lower thigh thaw loss and breast ash content.

 Figure 3. Fast-growing broiler meat and Slow-growing broiler meat  

 Source: https://chicken.org.au/ and  https://umitochi.com.au/product/aurum-poultry-co-slow-grown-cockerel-maryland/

Genetic Influence on Chicken Behavior and Health

Research shows that meat chickens and laying hens have different physical and behavioral needs (Rault et al., 2016). For example, fast-growing meat chickens prefer to stay near feeders rather than forage outside, unlike laying hens. This behavior is due to genetic differences, as broilers are bred for rapid growth and efficient feed conversion (Gadzama, 2024a), while layers are bred for egg production (Rault et al., 2016). Broilers tend to sit and eat more, gaining weight faster, but are not good at foraging and often face heart challenges (Jacobs et al., 2023).

Studies have found that meat chickens have lower-ranging behavior compared to laying hens (Larsen et al., 2018). This is because of differences in their genetics, age, breed, and how long they have access to outdoor ranges. Allowing meat chickens to go outside can help them explore more and be more active, which is good for their welfare (Gadzama, 2024b). However, getting meat chickens to spend time outdoors can be difficult for farmers (van de Weerd et al., 2009). More research is needed to find the best ways to encourage fast-growing meat chickens to use outdoor ranges. 

Conclusion

In conclusion, modern chickens are bred for either egg production (layers) or meat production (broilers), with fast-growing strains like Ross or Cobb commonly used in Australia and slow-growing strains used in Europe due to legislation. Slow-growing chickens are more active and forage more, reaching market weight at 12 weeks, while fast-growing chickens reach slaughter weight at 5 to 6 weeks. Good litter management is essential for producing healthy broilers and ensuring proper welfare conditions, especially in NAE (No Antibiotics Ever) programs. While reusing litter for multiple flocks is common, it poses risks such as increased moisture and ammonia levels. Effective litter management practices are crucial for creating good litter conditions and promoting animal welfare.

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