Data sheets: Calcium carbonate

Introduction

Calcium carbonate (CaCO₃) is the most commonly used source of Ca in swine feed. It is generally obtained from very pure deposits (>95% CaCO3) of limestone, with a Ca content ranging from 36-38%, which contains smaller amounts of impurities or traces of other minerals. However, CaCO₃ can also be found from chemical synthesis (obtained by precipitation as a by-product of the chemical industry), which is less common in swine feed.

In nature, the most abundant calcium source on the earth's surface is found in the sediment layers formed by limestone rocks that originated millions of years ago. These limestone rocks are mostly made up of calcium carbonate (CaCO₃), a whitish-colored mineral with a granular appearance which, after processing (extraction, selection, separation of impurities, coarse crushing, and grinding) and classification by particle size (by means of a sifting system), is used as a source of Ca. For swine feeding, fine fractions (<1.4 mm (~90%), <1.0 mm (~8-9%), and <0.5 mm (<1%)) are usually used.

Ca can easily interact with several minerals present in the deposits, such as phosphorus, sulfur, zinc, copper, magnesium, iodine, manganese, and cobalt. The ionic nature of these elements promotes the formation of insoluble complexes that precipitate and impede their intestinal absorption and availability. Hence, despite being one of the lowest cost ingredients in swine formulas, one must not lose sight of the need to use a quality source and have a well-analyzed chemical composition, so quality and standardization (or minimizing variability between batches) is very important.

Apart from Ca content and traces of other elements, it is also essential to control moisture to avoid management problems in the feed mill. It is also important to determine the solubility in HCl (0.2N), as an indirect measure of Ca digestibility, since this can vary between batches and origins (quarries). Finally, it is important to mention that, as it is a product extracted from geological deposits, it is necessary to ensure that other toxic compounds, such as heavy metals or dioxins, which may have accumulated in the deposits over time, are not also present.

Ca is necessary and important for the proper development of pigs, but it is necessary to be precise in the levels of inclusion, since its competition with P can generate problems at the intestinal absorption level due to an imbalance in the Ca:P ratio. Additionally, carbonate has a high buffering capacity that can hinder proper acidification in the stomach and compromise the digestibility of the protein and the acid-base balance, altering the electrolyte balance, especially in piglets at weaning. It is important to point out that since it is a low cost ingredient, it is often used as a support or diluent for most additives and micro-ingredients or supplements, so if these characteristics are not taken into account, specially in early stages, it can work against the efforts made when formulating.

Comparative study of nutritional values

The systems used in the comparison are: FEDNA (Spain), CVB (the Netherlands), INRA (France), NRC (United States), and Brasil (Brazil).

¹For the INRA and NRC evaluation systems the range of values (minimum and maximum) is presented resulting from the integration of the different classifications that these evaluation systems consider basically based on the Ca content, which differs mainly according to the geological origin or characteristics of the deposits extracted.

²For the CVB and INRA evaluation systems, only the calcium value is presented without considering the possible traces of other residual minerals.

Despite the importance of Ca in swine diets, with calcium carbonate being the main source, Ca content or richness is the only common parameter considered by all the evaluation systems studied (FEDNA, CVB, INRA, NRC, and BRASIL). The Ca content considered by most of the systems is very similar, with an average value of 38.2% Ca, if the lowest values considered by INRA and NRC are not taken into account. These two systems present lower quality extremes with lower values (35 and 35.8%, respectively). Unlike the rest of the ingredients (with the exception of salt), these differences are basically explained by the geological origin and characteristics of the extraction site, since, being a low-cost ingredient, consumption is regional and there is no export, so each valuation system adheres to what is available in its area.

It is observed that FEDNA and NRC are the only evaluation systems studied that characterize the content of minerals and metals (P, Na, Cl, K, Mg, S, Fe, Cu and Mn) (although this is not usual), which appear as impurities from the extraction process; having them classified is of interest because of the implications and interactions that they may represent. The contents on minerals found at a lower frequency are very similar between both evaluation systems except for the Mg content, for which NRC presents much higher values than FEDNA or BRASIL (between 5 and 7 times more), independently of the quality of CaCO₃ presented. This can be explained by the fact that the deposits extracted in the USA may come from sources that are more dolomitic, with a higher Mg content.

Lastly, in terms of Ca utilization and availability, as shown in the table, FEDNA is the only system that presents values for total apparent, standardized, and true digestibility.

Finally, it is important to consider that, given the importance of Ca and the implications associated with the source used, CaCO₃ is, for the moment, not very well described and taken into consideration by most valuation systems. One reason for this is the difficulty of generalizing and standardizing values, due to the changing and evolving nature associated with extraction from a regional deposit with regional consumption and at a low cost, which makes it difficult to justify additional transport and characterization costs beyond legal compliance (quality and toxicity).

Recent findings

1. Standardized total tract digestibility of calcium varies among sources of calcium carbonate, but not among sources of dicalcium phosphate, but microbial phytase increases calcium digestibility in calcium carbonate

The hypothesis of the present work was that standardized total tract digestibility (STTD) of Ca and the response to microbial phytase is constant among different sources of Ca carbonate and that the STTD of Ca is constant among different sources of dicalcium phosphate (DCP) when fed to growing pigs. The observed values for STTD of Ca were higher with microbial phytase supplementation (77.3% to 85.4%) compared with diets without exogenous phytase (70.6% to 75.2%), and values for STTD of Ca differed among the 4 sources of Ca carbonate. The digestibility of Ca and P in DCP appears to be constant regardless of origin of DCP. In conclusion, use of microbial phytase reduces the basal endogenous loss of Ca and increases Ca digestibility in Ca carbonate. The STTD of Ca varies among sources of Ca carbonate, regardless of phytase inclusion, but that appears not to be the case for the STTD of Ca in different sources of DCP.

2. Effects of limestone inclusion on growth performance, intestinal microbiota, and the jejunal transcriptomic profile when fed to weaning pigs.

To better understand the possible mechanisms underlying detrimental effect of including limestone in weanling diets, the possible impact on growth performance, colonic microbiota and, jejunal gene expression was studied. The results of the study reported that high levels of limestone inclusion in weaning diets, decreases growth performance without affecting feed intake in weaned pigs. Moreover, the addition of limestone to diets for 14 d after weaning can upregulate the expression of genes related to the inflammatory response, and enlarge colonic beta-diversity with an increased Bacteroides genera.

3. Particle size of calcium carbonate does not affect apparent and standardized total tract digestibility of calcium, retention of calcium, or growth performance of growing pigs

The effect of particle size of calcium carbonate used in diets fed to growing pigs on the apparent total tract digestibility (ATTD), standardized total tract digestibility (STTD), and retention of Ca among diets containing calcium carbonate was evaluated. Moreover, the impact on growth performance of weanling pigs due to the particle size of calcium carbonate was also assessed. The result reported indicated that ADG, ADFI, and G:F were not impacted by the particle size of calcium carbonate. On the other hand, particle size of calcium carbonate did not affect ATTD of Ca, STTD of Ca, or retention of Ca; ATTD of P or retention of P. Any particle size of calcium carbonate in the range from 200 to 1,125 μm can therefore be used in diets fed to pigs.

4. Basal endogenous loss, standardized total tract digestibility of calcium in calcium carbonate, and retention of calcium in gestating sows change during gestation, but microbial phytase reduces basal endogenous loss of calcium.

The present work was performed to test the hypothesis that the standardized total tract digestibility (STTD) of Ca and the response to microbial phytase on STTD of Ca and apparent total tract digestibility (ATTD) of P in diets fed to gestating sows are constant throughout gestation and if that the retention of Ca and P does not change during gestation. Based on the reported results it was concluded that Ca retention was less negative and ATTD of P tended to increase with supplementation of microbial phytase to the Ca-free diet regardless of gestation period. The basal endogenous loss, STTD of Ca, ATTD of P, and retention of Ca and P in gestating sows change during gestation with the greatest digestibility values observed in late gestation.

5. Availability of calcium from skim milk, calcium sulfate and calcium carbonate for bone mineralization in pigs.

There is little evidence that this calcium is as available as milk calcium for making bone. The availability of calcium was studied by monitoring bone parameters in 2-month-old pigs fed restricted amounts of calcium (70% RDA) for 2.5 months. The 3 main (> or = 50% Ca intake) Ca sources were either CaCO₃ or CaSO₄ or skim milk powder (29% of the diet). The bones of the pigs fed the "milk" diet had higher (P < 0.01) ash contents, breaking strength and density (DEXA) than those of the two others groups, in which the bone values were similar. Thus, the calcium provided by a diet containing milk appears to ensure better bone mineralization than do calcium salts included in a non-milk diet. The calcium restriction may have enhanced some milk properties to stimulate calcium absorption in these young, rapidly growing pigs.

References

FEDNA: http://www.fundacionfedna.org/
FND. CVB Feed Table 2019. http://www.cvbdiervoeding.nl
INRA. Sauvant D, Perez, J, y Tran G, 2004, Tables de composition et de valeur nutritive des matières premières destinées aux animaux d'élevage.
NRC 1982. United States-Canadian Tables of Feed Composition: Nutritional Data for United States and Canadian Feeds, Third Revision.
Rostagno, H,S, 2017, Tablas Brasileñas para aves y cerdos, Composición de Alimentos y Requerimientos Nutricionales, 4° Ed.