Towards precision feeding in laying hens: Update and validation of a mathematical model to predict daily calcium and phosphorus flows

In laying hens, precision feeding could consist in providing an optimal calcium supply (level, source, and distribution kinetics) to ensure the well-being and longevity of animals (i.e. limiting osteoporosis and bone fractures) while maintaining eggshell quality. During eggshell synthesis (occurring mostly by night), hens can mobilize calcium from bones stored in a specific structure called the medullary bone. The calcium stock is then rebuilt after oviposition. However, the animal cannot always fully compensate for a supply deficiency in calcium from feed. An intense and repeated mobilization / reconstitution of the medullary bone can thus lead to long-term and severe lesions affecting the animal’s skeleton. To better understand and predict daily calcium requirements, and minimize bone mobilization, an existing mathematical model [1] describing calcium and phosphorus fluxes in the different compartments of the animal (i.e. digestive tract, blood, bone, and egg) was implemented and adapted. The main adaptation of the existing model was to include the ability to simultaneously consider different calcium sources (i.e. meal vs. particles) with different associated solubilization rates. An experimental trial involving 288 Lohmann Tradition laying hens from 19 to 33 weeks of age was conducted. Six different dietary treatments were tested (4 pens of 12 hens/treatment). They differed according to the form of calcium carbonate (i.e. meal, two different particle sizes, or a mix of meal and particles) and to the relative amount of feed distributed in the morning and in the afternoon (30:70 or 70:30). Three sampling series at 27, 30, and 33 weeks of age were performed to measure ionic calcium and inorganic phosphorus blood concentrations over 24 hours (3 to 6 samples per hen). The model was then calibrated and subsequently validated according to these measured concentrations. In its current state, the model can be seen as a decision support system (DSS) for the precision feeding in laying hens, giving to the user an insight on what could be the best feeding strategies to maintain animal longevity, increase well-being or even reduce feed cost, at the scale of an individual hen. In the future, this model could also be implemented in a new tool, taking into account the variability among birds (e.g. oviposition time), to identify the best feeding strategies at the flock level. [1] Kebreab et al. (2009). Poultry Science, 88 (3), 680–689.