The influence of multifunctional platforms and heat stress on broiler chicken bone health and lameness

The skeletal health of broiler chickens is a key concern due to their rapid growth rates, which often lead to leg weakness, impacting both animal welfare and production efficiency. Heat stress further compromises bone development by disrupting bone metabolism. Environmental enrichment may increase broiler activity and thereby improve skeletal health. In this study, we evaluated the effects of a multifunctional platform (providing local cooling, shelter, and manure separation) on leg bone development under thermoneutral and heat stress conditions. Three production cycles were conducted using 560 male Ross 308 broilers, evenly assigned to four pens and reared for 43 days. The stable was divided into a thermoneutral and heat-stressed compartment, each containing an enriched and barren pen. Heat stress (32°C for 6 h/day) was applied from day 29 to 40, excluding weekends (days 34-35). Gait scoring was performed on day 40. On day 43, birds were euthanized for bone morphometric, mechanical, and histological analyses. Enrichment and temperature interactions affected femur (p = 0.022) and metatarsus (p = 0.011). Under heat stress, broilers in barren environments had longer bones than those in enriched or thermoneutral conditions (p < 0.05). Broilers under thermoneutral conditions with platform access demonstrated better gait scores (p = 0.003). Furthermore, gait scores showed moderate positive correlations with metatarsus width (R = 0.46), tibiotarsus width (R = 0.45), and femur width (R = 0.45). Regression analysis indicated that higher gait scores were associated with longer and wider bones (p < 0.001). Bone mechanical testing showed interactions for maximum force (p = 0.005) and breaking force (p < 0.001), both higher in broilers under thermoneutral conditions with platform access. Histological analysis revealed an expanded proliferation zone of the growth cartilage in heat-stressed broilers with platform access (p < 0.001). Overall, platforms improved gait and bone strength primarily under thermoneutral conditions, while these benefits were not evident under heat stress. This highlights that platforms alone are insufficient to mitigate heat stress-induced skeletal challenges, indicating the need for complementary strategies to protect broiler leg health in warmer environments.