Calcium Nutrition of Broilers: Current Perspectives and Challenges
Aaron Cowieson - The benefits of using standardized digestibility is exactly as you say, but I was of the impression that using Ileal instead of total tract digestibility was more a matter of convenience. We already collect illegal samples for SID of amino acids, and using those same samples for mineral analysis as well is simply easier than collecting a separate excreta sample. Particularly when the birds are being raised in floor pens where collection of excreta without contamination from the litter is more difficult. After all, on the swine side of things, the NRC in 2012 moved to Standardized Total Tract Digestibility for P and Ca. Collecting individual fecal samples is much easier for swine than for poultry, and as such using Ileal samples (which are usually only collected in the case of cannulated pigs) is no longer the more convenient option.
Gene Pesti, as evidenced by several research works (Zhand & Adeola, 2017; 2018; Fang et al., 2007 – poultry and pigs) and pointed by Aaron Cowieson, SID Ca/P is more additive in complex mixtures. Some nutrient recommendations have already started using SID P (NRC, 2012) in feed formulations as pointed by Joshua Jendza. Therefore, a concurrent use of SID Ca is necessary because of the interrelationship between Ca and P in the absorption and post-absorptive utilisation of these minerals. Excess P excretion and environmental pollution are reduced by the use of SID P which is a major benefit. In case of pigs, I like to point out that the Ca digestibility measured at both ileal- and total tract- level in pigs was similar as indicated by Zhang et al. (2016). Ca absorption is mostly completed in the jejunum irrespective of dietary Ca concentrations (Mutucumarana et al., 2014), but may be in the upper ileum sometimes (Hurwitz and Bar, 1970)? So, there is no possibility of mineral absorption in the second half of the ileum, I think. I don’t have direct practical experience with studies related to biological responses. But I do have a question regarding ‘highly available mineral source’. Because the availability of limestone was assumed to be 100% earlier. But this is not the case based on the recent digestibility studies.
Alvaro Dubois – Ca digestibility/excretion can be affected by several factors and therefore it is a complex subject, I think. As you said, dietary Ca concentration could be one of the factors. Dietary P, phytate, basal diet type, age & class of birds are some other factors which may influence Ca digestibility. I think, the digestibility/excretion trend of Ca cannot be compared directly with that of P.
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