Particle size is an important consideration for some feed ingredients in pig diets. Reducing the particle size of cereal grains and soybean meal in diets fed to pigs improves digestibility of energy, amino acids, and other nutrients, because feed ground to smaller particle sizes has more surface area on which digestive enzymes can work.

The particle size of inorganic calcium sources has been shown to affect calcium retention in poultry. Particle sizes of 1.00 mm or greater are recommended to optimize calcium retention and eggshell quality in laying hens, but coarse particle sizes result in reduced calcium retention in broiler chicks.  However, little is known about the effect of particle size of calcium sources fed to pigs. Therefore, an experiment was conducted to test different particle sizes of calcium carbonate and determine which size optimizes calcium digestibility and retention by growing pigs.

Forty growing barrows with an average initial body weight of 15.42 kg were fed one of five diets based on corn and potato protein isolate. One diet was calcium free, and was used to estimate basal endogenous losses of calcium. The other four diets contained supplemental calcium carbonate ground to four different particle sizes (approximately 200, 500, 750, and 1125 microns). The four experimental diets were formulated to contain identical amounts of calcium.

No significant differences were observed among the four diets for calcium retention, ATTD of calcium, or STTD of calcium (Table 1). The ATTD of calcium was 69.98%, 74.28%, 69.96%, and 72.07% for diets containing calcium carbonate with particle sizes of 200, 500, 700, and 1125 microns, respectively. The STTD of calcium was 74.15%, 78.45%, 74.13%, and 76.24% for diets containing calcium carbonate with particle sizes of 200, 500, 700, and 1125 microns, respectively. Calcium retention was 67.39%, 70.40%, 63.93%, and 67.18% for diets containing calcium carbonate with particle sizes of 200, 500, 700, and 1125 microns, respectively.

• Particle size of calcium carbonate did not affect calcium digestibility or retention of calcium by growing pigs.
• Based on the results of this study, producers do not need to be concerned with particle size of calcium supplements in growing pig diets.

Table 1. Apparent (ATTD) and standardized (STTD) total tract digestibility of calcium in diets containing four different particle sizes of calcium carbonate fed to weanling pigs

^abMeans within a row not sharing a common superscript are different (P < 0.05).

This report is based on unpublished research by Laura Merriman and Hans H. Stein.