Calcium Nutrition of Broilers: Current Perspectives and Challenges
Published:July 7, 2023
Summary
1. Introduction Humphry Davy, a British chemist, was the first to isolate and investigate the chemistry of calcium (Ca) and to recognise it as an essential component of bone in 1808. Ever since, it has been the subject of a voluminous amount of research in both human and animal nutrition. Today, the biological significance and economic importance of Ca in animals are intuitive. Calcium is the ...
I am just curious, would someone please explain to me the logic of SID Ca or P? I understand that SID assays were developed for amino acid "digestibility" in chicks from assays with pigs. In pigs there is considerable fermentation in the handout so ileal canulas avoid that problem. It isn't practical to cannulate the end of the ileum in chicks, so half of the ileum was chosen as a substitute. For standardization purposed it was deemed acceptable to assume there is no amino acid absorption from the second half of the ileum. But with minerals there is no concern with bacteria changing them or volatilization. What is the rationalization for assuming no mineral absorption from the second half of the ileum?
There is also a fourth method that I think used to be the standard. Biological responses to graded levels of a highly available mineral source were compared to the source in question. Bone ash was most often the biological response of choice and the assays gave acceptably precise estimates of mineral availability. The precision and repeatability of the various methods should be the important criteria.
Gene Pesti the main benefit of SID systems is that they are more additive in complex mixtures. There is a lot of published work showing that considering basal endogenous loss of the focal nutrient makes LCF more precise. AID systems tend to under-estimate the nutrient concentration in the finished feed because basal endogenous loss has been considered multiple times in the estimation of the digestibility of individual ingredients. This is more problematic for nutrients that are found at high concentrations in basal endogenous flow e.g. threonine but admittedly less relevant for e.g. calcium. Still, I think moving to SID is useful in most cases and standardising the assay methodology makes sense so we can compare across labs?
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.
Dear Dr. Pesti. It's an interesting question. The rationale seems to me the same we use for energy. When measured at ileal level, we are talking about digestible energy (or total tract for swine). When measured in excreta (total tract collection), we call it metabolizable because part of it has been absorbed, metabolized and excreted via urine (mainly as N). For phosphorus (P), which is excreted in sizable amount via the kidneys (except in deficient diets), there would be a confusion between digestibility and excretion, being the later heavily influenced by the amount in the diet and requirement. For calcium, the same principle applies although, to my understanding, the proportion of intake excreted via kidneys is usually smaller than for P (at regular intakes of both Ca and P), and so digestibility (at ileal level) is more heavily influenced by the amount supplied than P. Looking for the authors' answer.
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.
Dear Laura David.
I just wanted to emphasize the importance of excretion via kidneys on the difference of measures made at ileum or total excreta collection methods. That this is different for Ca and P, I totally agree with you.
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