It is important that the digestibility of Ca in Ca sources is known to formulate diets based on values for digestible Ca rather than total Ca. Only a small amount of the Ca required by pigs is provided by plant-based ingredients and supplementation of Ca from Ca phosphates and Ca carbonate, is usually required to meet the requirement by pigs. In addition, use of microbial phytase increases Ca digestibility in Ca carbonate, which is one of the major sources of Ca in pig diets.

Differences in Ca digestibility in 4 sources of Ca carbonate produced in the United States have been observed, but it is unknown if there are differences in the ATTD of Ca in calcium carbonate sources produced outside the United States. Therefore, the objective of this experiment was to test the hypothesis that there are differences in the apparent total tract digestibility (ATTD) and standardized total tract digestibility (STTD) of Ca and in the response to microbial phytase among 20 sources of Ca carbonate obtained from different parts of the world.

Experimental design

A total of 40 diets were formulated based on corn, potato protein concentrate, and Ca carbonate. Twenty sources of Ca carbonate were obtained from different regions of the world, including the United States (n = 4), Europe (n = 7), Asia (n = 6), and South Africa (n = 3). Each source of Ca carbonate was used in two diets, one diet without microbial phytase and one diet that contained 1,000 phytase units/kg of diet (FYT; HiPhos, DSM, Kaiseraugst, Switzerland). Crystalline amino acids, vitamins, and minerals were included in all diets to meet requirements for 11 to 25 kg pigs (NRC, 2012).

A total of 320 barrows (body weight: 17.47 kg; SD = 1.28) were allotted to the 40 diets. Pigs were housed individually in metabolism crates and fecal samples were quantitatively collected using the marker to marker procedure. Daily feed allotments were divided into two equal meals that were provided at 0800 and 1600 h, and pigs were provided feed in the amount of 3.0 times the maintenance requirement for metabolizable energy. Pigs had free access to water throughout the experiment.

The ATTD of Ca in experimental diets were calculated based on intake and fecal output of Ca. The STTD of Ca in each experimental diet was determined by correcting the ATTD of Ca for an average basal endogenous loss of Ca (i.e., 433 mg/kg dry matter intake) obtained by Lee and Stein (2023). Digestible Ca in source was calculated by multiplying the concentration of Ca in source by the STTD of Ca and diving by 100.

The initial statistical model included Ca carbonate source, phytase, and the Ca-source × phytase interaction as fixed effects; however, no interactions between Ca source and phytase were observed. Therefore, the final statistical model included only Ca source and phytase as fixed effects. A second analysis was performed to compare digestibility of Ca carbonate obtained from different regions of the world (i.e., Europe, Asia, United States, and South Africa). In this model region, phytase, and the region × phytase interaction were fixed effects. However, no interactions between region and phytase were observed and therefore, the final statistical model included only region and phytase as fixed effects. Means were calculated, and least significant differences were used to separate the means. Statistical significance and tendency were considered at P < 0.05 and 0.05 ≤ P < 0.10, respectively.

Results

Concentrations of Ca in the 20 sources of Ca carbonate ranged from 32.1 to 40.9% and the average Ca concentration in Ca carbonate sources was 37.5% (Table 1).

Differences in the ATTD and STTD of Ca were observed among pigs fed diets containing different sources of Ca carbonate (P < 0.001; Table 2). Pigs fed diets containing 1,000 FYT had greater (P < 0.001) ATTD and STTD of Ca compared with pigs fed diets containing no phytase. The ATTD and STTD of Ca in Ca carbonate from the United States was less (P < 0.001) than in Ca carbonate from Europe, Asia, or South Africa.

In conclusion, differences in ATTD and STTD of Ca were observed among Ca carbonate obtained from four regions of the world, and inclusion of microbial phytase increased the ATTD and STTD of Ca in Ca carbonate regardless of the region where the Ca carbonate was produced.

Key points

• The average concentration of Ca in 20 sources of Ca carbonate was 37.5% and the CV was 5.11%.
• There were no interactions between Ca carbonate source and phytase or region and phytase, which means that the use of phytase increases the STTD of Ca and digestible Ca in Ca carbonate regardless of sources or region.
• The STTD of Ca in 20 sources of Ca carbonate from Asia, Europe, South Africa, and the United States ranged from 65 to 81% without phytase and 77 to 90% with phytase.
• The standardized total tract digestible Ca in 20 sources of Ca carbonate from Asia, Europe, South Africa, and the United States ranged from 24 to 33% without phytase and 28 to 36% with phytase.
• The STTD of Ca and digestible Ca in sources procured from the United States were lower than in sources from Asia, Europe, and South Africa.

Table 1. Analyzed Ca in 20 sources of Ca carbonate, as-is basis

Table 2. ATTD and STTD of Ca and digestible Ca in 20 different sources of Ca carbonate