Factors affecting the digestibility of calcium in feed ingredients and requirements for digestible calcium by pigs

Eight experiments were conducted to understand factors that may affect the digestibility of Ca in diets fed to pigs and also to determine the requirement of Ca for the finishing pig. The first experiment was conducted to determine the apparent total tract digestibility (ATTD) and the standardized total tract digestibility (STTD) of Ca in feed ingredients of animal origin without and with microbial phytase. Results from Exp. 1 indicated that if no phytase was used, the ATTD and STTD of Ca in poultry byproduct meal were greater (P < 0.05) than in meat and bone meal and meat meal, but values for poultry meal were not different meat and bone meal, meat meal, and poultry byproduct meal. However, if phytase was added to the diets, no differences in ATTD or STTD of Ca among ingredients were observed (interaction P < 0.05). There was no effect of microbial phytase on ATTD or STTD of Ca in the 4 ingredients. The second and third experiments were conducted to determine if particle size of calcium carbonate influences the STTD of Ca or growth performance. Results from these 2 experiments indicated that particle size did not influence STTD of Ca or growth performance. The STTD of Ca was 74.15 ± 3.24%, 78.45 ± 2.71%, 74.13 ± 2.93%, and 76.24 ± 2.66% for diets containing Ca carbonate ground to an average particle size of 200, 500, 700, or 1125 µm. The fourth experiment was conducted to determine the effect of supplementing diets fed to growing pigs with fat sources that differ in their concentrations of saturated and unsaturated fatty acids on the ATTD of Ca. Results indicated that the ATTD of Ca was greater (P < 0.05) for pigs fed diets containing soybean oil, corn oil, palm oil, or tallow than for pigs fed a basal diet without the addition of fat or a diet containing choice white grease. The fifth experiment was conducted to determine if increasing concentrations of sodium chloride (NaCl) affect the ATTD or retention of Ca and P in diets fed to growing pigs. Results indicated that increasing dietary inclusion of NaCl above 0.4% reduced (P < 0.05) Ca intake, Ca absorbed, ATTD of Ca, and retention of Ca. The concentrations of Ca in feces and urine were greater (P < 0.05) if phytase was not included in the diet; but Ca absorption, ATTD of Ca, and retention of Ca were increased (P < 0.05) by addition of microbial phytase. The sixth experiment was conducted to determine the effect on the digestibility of Ca in calcium carbonate of including sucrose or cornstarch in diets for growing pigs. Results indicated that the ATTD of Ca was not affected by inclusion of increasing concentrations of sucrose in the diets. Likewise, no effects of sucrose inclusion were observed for feed intake, fecal output, fecal Ca concentration, Ca intake, absorbed Ca, urine Ca, or Ca retention. Sucrose inclusion tended to affect fecal calcium output (g/d; P = 0.066) and fecal output (g/d; P = 0.081) quadratically with the greatest values being calculated for diets containing 20 or 40% sucrose. The seventh experiment was conducted to test the hypothesis that precipitation of Ca from calcium carbonate in diets based on cornstarch may be different from that of diets based on corn, and to determine the influence of phytase on the digestibility of Ca in both types of diets. Results from this experiment indicated that phytate in corn decreases (P < 0.05) the ATTD of Ca, but phytase had no effect on the ATTD of Ca regardless of the concentration of fiber in the diet. The final experiment was conducted to determine the digestible Ca requirement for pigs from 100 to 130 kg. Results from the experiment support the current requirements for Ca and STTD P, and feeding Ca at levels greater than the requirements (0.46% total Ca; 0.29% STTD Ca) is detrimental to growth performance of pigs. Additional research is needed to determine the STTD Ca requirements if different concentrations of phytase are included in the diet