Rundle, Carly M., Barthold Hillen, Yueming Dersjant-Li, Anne-Marie Debicki-Garnier, Hans H Stein. 2020. The effect of increasing phytase dose to 1000 FTU/kg on phosphorous and calcium digestibility in pigs fed diets without inorganic P. J. Anim. Sci. 98(Suppl. 4): 100-101. doi.org/10.1093/jas/skaa278.184. (Abstr.). Link to abstract.

Lee, Su A, Mike R. Bedford, Hans H. Stein. 2020. Dietary calcium decreases digestibility of phosphorus in late gestating sows, but blood biomarkers may be used to predict bone formation and resorption. J. Anim. Sci. 98(Suppl. 3): 105. doi.org/10.1093/jas/skaa054.179.(Abstr.). Link to abstract.

Lee, Su A.,  L. Vanessa Lagos, Mike R. Bedford, and Hans H. Stein. 2020. Increasing calcium from deficient to adequate concentration in diets for gestating sows decreases digestibility of phosphorus and reduces serum concentration of a bone resorption biomarker. Journal of Animal Science, 2020,  Vol. 98: No. 3:1-8.

Lee, Su A, L. Vanessa Lagos, Carrie L. Walk, and Hans H. Stein. 2019. 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. J. Anim. Sci. 2019.97:3440–3450.

Lee, S., C. Walk, and H. Stein. 2018. Sows in mid-gestation have reduced digestibility and retention of calcium and phosphorus compared with growing pigs. 14th International Symposium on Digestive Physiology of Pigs. Adv. Anim. Biosci. Volume 9, Issue S2, 9:S193-194. (Abstr.). Link to abstract

Lee, S. A., L. V. Lagos, and H. H. Stein. 2019. Digestible calcium and digestible phosphorus in swine diets. In Proc. London Swine Conference, London, ON, Canada. March 26-27, 2019. Pages 63-72. Link full text(.pdf)

Requirements for P for growing pigs are expressed as the requirement for standardized total tract digestible (STTD) P, whereas requirements for Ca are usually expressed as requirements for total Ca. It is, however, recognized that diets for pigs are most accurately formulated based on a STTD Ca:STTD P ratio, and recent work has generated values for STTD of Ca in most Ca containing feed ingredients, which makes it possible to formulate diets based on STTD Ca.

Recent data from the University of Illinois have indicated that if STTD P is at the requirement, a ratio between STTD Ca and STTD P that is less than 1.35:1, 1.25:1, and 1.10:1 maximizes growth performance of pigs from 25 to 50 kg, 50 to 85 kg, and 100 to 130 kg, respectively. However, the STTD Ca:STTD P ratio needed to maximize bone ash is greater than the ratio needed to maximize growth performance. An attempt to estimate the requirement for STTD Ca by pigs from 11 to 25 kg was also made, but due to a reduction in ADG and G:F as dietary Ca increased, an optimal STTD Ca:STTD P ratio could not be estimated.

Calcium may be absorbed by transcellular or paracellular transport. Transcellular transport is the primary route if dietary Ca is low, but if dietary Ca is adequate or high, Ca is mainly absorbed using the paracellular route via the tight junctions. However, there are limited data demonstrating effects of dietary Ca concentration on abundance of genes related to transcellular and paracellular transport of Ca in the small intestine of pigs.

Therefore, the objectives of this experiment were to test the hypotheses that a STTD Ca:STTD P ratio less than 1.40:1 maximizes growth performance of pigs from 11 to 25 kg and that increasing dietary Ca downregulates abundance of genes related to transcellular absorption of Ca and tight junction proteins in the small intestine.

Standardized total tract digestibility (STTD) of Ca has been determined for most Ca containing ingredients fed to growing pigs, but the basal endogenous loss of Ca is greater and the STTD of Ca in sows in mid-gestation are less than in growing pigs. As a consequence, if diets for gestating sows are formulated using STTD values determined in growing pigs, the provisions of digestible Ca may be less than anticipated.

The efficacy of phytase to release Ca and P is believed to be influenced by the physiological state of pigs with phytase fed to sows in mid-gestation releasing less Ca and P compared with growing pigs or sows in late-gestation. However, it is not known if values for STTD of Ca or retention of Ca and P that are measured in one period of gestation are representative of the entire gestation period.

Therefore, an experiment was conducted to test the hypothesis that the STTD of Ca from calcium carbonate and the response to microbial phytase on STTD of Ca and apparent total tract digestibility (ATTD) of P in corn-based diets fed to gestating sows are constant throughout the gestating period for sows. The second objective was to test the hypothesis that retention of Ca and P does not change during gestation.

Merriman, L. A., C. L. Walk, M. R. Murphy, C. M. Parsons, and H. H. Stein. 2017. Inclusion of excess dietary calcium in diets for 100- to 130-kg growing pigs reduces feed intake and daily gain if dietary phosphorus is at or below the requirement. J. Anim. Sci. 95:5439-5446. Link to abstract