ISSUE FOCUS 58 FEED & ADDITIVE MAGAZINE February 2026 USING BLOOD BIOMARKERS TO ADJUST FEED FORMULATIONS Even though Ca levels are hormonally regulated, blood Ca and P does respond to dietary inputs. Parathyroid hormone, calcitonin and vitamin D will regulate blood Ca levels to some extent, but not completely. Figure 6 shows a statistically significant association between dietary Ca and plasma Ca. This has also been shown for P (Figure 7). Interestingly, whilst dietary P has an influence on blood P, diet Ca is capable of influencing both Ca and P. Specifically, over-feeding dietary Ca has a supressing effect on blood P and vice versa. Whilst dietary Ca and P do have some influence on blood Ca and P, blood pH and acid/base balance may be more important in order to optimise blood Ca and P concentrations. For example, the proportion of total blood Ca that is metabolically active and can contribute to skeletal mineralisation is normally around 47-48% in broilers. However, this can drop by 2-4% for every 0.1 unit increase in blood pH. These interactions highlight the importance of monitoring biomarkers beyond blood Ca and P when attempting to optimise the nutrition and health status of the bird. A common disturbance to optimal blood pH in commercial broilers is high chloride intake. Chlorine based sanitizers and water treatments are not unusual, plus sources of chloride are used in the feed. These can all, inadvertently, push blood pH down which might have negative implications, not only for Ca and P, but for renal health, litter quality and growth rate. Nutritionists need to understand the balance between cations and anions, and use them as levers within the least-cost formulation strategy to produce desirable outcomes. 15.0 14.0 13.0 12.0 11.0 10.0 9.0 13.5 Total calcium in feed, % Venous plasma calcium, mmol/L 12.9 1.67 1.39 1.20 1.11 1.01 0.84 0.80 0.60 13.7 11.7 13.0 12.1 12.0 11.9 Figure 6. Relationship between dietary calcium and blood calcium in broilers (Source: Walk et al., 2022) 6.0 5.0 4.0 3.0 2.0 1.0 0.0 4.6 Total phosphorus in the diet, % Venous plasma phosphorus, mmol/L 0.50% 0.65% 5.4 Figure 7. Relationship between dietary phosphorus and blood phosphorus in broilers (Source: Walk et al., 2022)
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