This literature review volume, focusing on egg-laying hen dietary supplementation, builds on the previous two sections:
Volume I - an informative overview and introduction to the potential of dietary interventions, and
Volume II - a summary of the dietary guidelines set forth by the National Research Council (NRC) and the role key nutrients play in hen bone health.
Dedicated sections are also added on the effects of hen body weight and feed intake rates on the required nutrient levels. The review provides an overview of the nutritional requirements of calcium, phosphorus and vitamin D3, nutrients key for optimal hen bone health. This volume also explores other nutrients and additives for their potential in helping hens develop stronger bones, ideally ones less prone to fractures. These include boron, copper, essential oils, magnesium, probiotics, selenium and vitamin D3 metabolites. Overall, this work is another step in the search for cost-effective dietary interventions to mitigate high keel bone damage (KBD) and fracture (KBF) risk in egg-laying hens.
All in all, this literature review volume is aimed at providing more insights into how nutritional interventions may fulfill the nutritional needs of egg-laying hens. Bone and eggshell properties are reported as proxies because fracture incidence reduction was typically not studied. Most of the research was also done with hens kept in cages, further complicating the direct transference of the data collected. In general, the fact that the 9th edition of NRC’s dietary guidelines is significantly outdated was confidently confirmed, suggesting that the recommendations by established breeders are a much better fit with the most recent research.
More specifically, monitoring hen body weight and ensuring the individuals in the flock attain good body scores could be an initial approach towards controlling the risk of fracture. When it comes to dietary formulation, however, it is critical to adapt the provided feed nutrient levels to the specifics of the particular flock, namely - the hens’ feed intake rates, which change as they age. Recommended calcium, phosphorus and vitamin D3 levels were provided. Despite scarce literature, out of the explored additional feed additives, supplementation with boron, copper, probiotics and, most notably, vitamin D3 metabolites showed the highest potential for improving hen bone strength. An overview of all studied additives can be found in the appendix.
The findings can help inform and direct egg producers and feed industry stakeholders towards helpful resources for ensuring that optimal diets are provided to the hens. It also shall serve as a starting point to develop dedicated case studies on welfare-oriented hen nutrition and questioning current practices.