Recent studies show that up to 97% of layer hens kept commercially can have at least one keel bone fracture. Additionally, these fractures can take up to eight weeks to heal, implying that the majority of hens suffer from these fractures for a significant portion of their lives. This issue can only be solved by using a combination of interventions to address problems in laying hen housing, nutrition, and genetics. In particular, laying hen nutrition has been extensively researched, and specific guidelines have been produced by the National Research Council: The Nutrient Requirements of Poultry among other institutions in the past. However, existing nutrition publications primarily focus on productivity and recommendations can become outdated quickly. It is also important to note that isolating the effects of one nutrient (e.g., increasing calcium to improve bone strength) without considering the full picture (e.g., cage-free vs caged housing) can lead to inaccurate results. This is especially true with respect to housing systems, which require knowledge tailored to each housing system, as well as any transitional periods.
This volume reviews The Nutrient Requirements of Poultry, including its recommendations across life phases and breeds. The last edition was published in 1994, and each publication update provides new recommendations. This volume also reviews the combined effects of housing systems and nutrition on bone health, as well as contributing factors for fracture risk across housing systems. Furthermore, recent research suggests that the internal pressure caused by egg laying may also contribute to higher incidences of fractures. As a result, solely improving housing (e.g., adding ramps) for cage-free hens may not adequately prevent fractures. However, emerging research shows caged hens may benefit from improved nutrition, yet these improvements cannot counteract the debilitating welfare issues caused by constraining their movement.
This second volume also reviews specific nutrients that support bone health: calcium, phosphorus, and vitamin D and assesses whether or not supplementation through feed fortification can improve bone health and hen welfare. However, it should be noted that amounts of each nutrient provided to hens via feed must be closely monitored for external factors (e.g., heat, age, breed, etc.) that can impact feed consumption and nutrient absorption. If levels are not monitored, hen welfare may decline (sometimes demonstrated by a rise in mortality) and production costs may rise. When properly monitored, phosphorus works in tandem with calcium to aid in eggshell formation and support bone health; however, a lack of research on phosphorus supplementation has led to its frequent over-supplementation on commercial farms. Similarly, vitamin D plays a key role in skeletal integrity, and is essential for the proper absorption and metabolism of calcium and phosphorus. Other supplemental nutrients such as phytase (an enzyme that enhances phosphorus digestibility) and omega-3 fatty acids (a group of fatty acids that slow down bone decay and promote reconstruction) may also improve bone health. Although further research is needed to determine to what extent these additives can benefit bone health, studies show lower rates of mortality with phytase supplementation and greater keel breaking strength when feeds are fortified with omega-3 fatty acids. In conclusion, feed fortification that also considers hens’ breed, housing system and other factors can provide significant benefits for hens’ bone health and welfare.