Modification of a limestone solubility method and potential to correlate with in vivo limestone calcium digestibility

Abstract

Work was done to modify a limestone solubility assay to improve predictions of in vivo apparent ileal digestibility of Ca (AID Ca) in broilers and impacts on AID P. Limestones (LIME) were obtained from 3 commercial sources. LIME-1 (0.633 mm mean diameter, GMD); LIME-2 (ground sub-sample of LIME-1, GMD = 0.063 mm); LIME-3 (GMD = 0.326 mm), and LIME-4 (GMD = 0.831 mm). Solubility was determined at 5, 15, and 30 min of incubation using either a 0.2 N HCl (S1) or a pH 3 HCl (pH = 0.26) solution buffered with 3 M glycine (S2) to mimic gizzard and proventriculus pH. An AID trial was conducted with 320 Ross 708 male broilers. Treatments (Trt) were no added LIME, or added LIME-1, 2, 3, and 4 to achieve 0.67% Ca, to a basal diet (no added inorganic P, 0.07% Ca) with or without 1,000 U phytase/kg (36 h, 23 to 24 D of age, n = 8, 4 birds/n). Distal ileal digesta was collected from all birds and pooled by pen. Irrespective of interaction, LIME solubilized quicker and more completely with S1 vs. S2 at all time points (P < 0.05). LIME-2 solubilized the quickest, while LIME-3 had the lowest solubility through all incubation times (P < 0.05). The AID Ca was 66.30, 47.46, 19.93, and 66.33% for LIME-1, 2, 3, and 4, respectively (0 U/kg, P < 0.05). Phytase inclusion increased AID Ca by 15% on average (P < 0.05). The AID P dig was highest in no LIME added diet (74.91%) and adding LIME reduced (P < 0.05) AID P to 23.14, 12.78, 65.47, and 37.40%, for LIME-1, 2, 3, and 4, respectively in the absence of phytase. Regression showed that GMD, 15- and 30-min solubility were critical for AID Ca (R2 between 0.978 and 0.988). In conclusion, the solubility dynamics including speed and extend of solubilization, rather than a single timepoint, yield better predictions for in vivo Ca digestibility of LIME.

Effects of calcium level and source, acidification, and phytase on phytate degradation and the microbiota in the digestive tract of broiler chickens

“…Overall, it seems that one major factor of P utilization affected by Ca sources and levels is the solubility of Ca from differing sources that depends, inter alia, on pH and microbiota. This supports conclusions reached by Kim et al [21] based on a comparison of CaCO 3 sources.…”

“…This is supported by the crop pH of 5.2 for Ca-formate and 5.5 for CaCO 3 , both being above the pH critical for complex formation [9]. As acidi cation can increase Ca solubility, CaCO 3 +formic acid probably had higher Ca solubility than CaCO 3 alone as a consequence of formic acid lowering the pH [21]. Formic acid supplementation would then make more Ca available for Ca-InsP 6 complex formation and thus reduce InsP 6 disappearance.…”

“…This amount was met at the high Ca level without phytase supplementation for CaCO 3 and CaCO 3 +formic acid, but for Ca-formate only when phytase was supplemented. Particle size [25,30] and Ca solubility [21] of Ca sources were shown to be a determinant of Ca utilization. Possibly, the considerably higher mean particle size of Ca-formate compared to CaCO 3 was more limiting for Ca utilization than the higher solubility of Ca-formate.…”

Coarse limestone does not alleviate the negative effect of a low Ca/P ratio diet on characteristics of tibia strength and growth performance in broilers

“…These results agree with our finding, indicating that particle size of limestone probably had an impact on P digestion, whereas it had less impact on Ca digestion. In an in vitro study to mimic the Ca solubilization in the GIT ( Kim et al., 2019 ), fine limestone initially released more Ca than coarse limestone; however, the same amount of Ca was released after 20 min (particle size < 75 and 402 μm for the fine and course limestone, respectively). This in vitro solubility finding is in line with the observed Ca digestibility in the present study, that is the Ca digestibility was higher for the fine limestone in the jejunum, and this difference disappeared in the ileum for the low Ca/P ratios but retained for the high Ca/P ratios.…”

Effects of calcium level and source, formic acid, and phytase on phytate degradation and the microbiota in the digestive tract of broiler chickens

“…This is supported by the crop pH of 5.2 for Ca-formate and 5.5 for CaCO 3 , both being above the pH critical for complex formation [ 9 ]. As acidification can increase Ca solubility, CaCO 3 + formic acid probably had higher Ca solubility than CaCO 3 alone as a consequence of formic acid lowering the pH [ 24 ]. Formic acid supplementation would then make more Ca available for Ca-InsP 6 complex formation and thus reduce InsP 6 disappearance.…”