By Hans Stein
Research being carried out at the University of Illinois and funded by AB Vista will significantly improve the accuracy of calcium (Ca) provision in growing pigs by generating much-needed standardised or true total tract digestibility (STTD or TTTD) values for Ca across a range of common feed ingredients.
"The aim is to achieve the same level of precision for Ca when formulating diets as is possible for phosphorus (P)," states Dr Carrie Walk, AB Vista's Senior Research Manager. "We formulate using digestibility values for the majority of the important – and expensive – nutrients in the diet, such as P and amino acids, but that data is currently not available for Ca in growing pigs."
The study will determine digestibility values both with and without the addition of a phytase, since any reduction in phytate-Ca binding through phytase use will increase Ca availability, leading to potential oversupply. "Although considered a relatively inexpensive nutrient, the implications of Ca oversupply are significant," Dr Walk adds. "Even marginally high levels of dietary Ca have been shown to increase gastric pH and reduce the digestibility of two of the most expensive nutrients, protein and P."
The initial phase of the project, which is being led by the University's Professor Hans Stein, used canola meal as the primary source of Ca. The trials generated Ca endogenous loss values of 0.160 g/kg dry matter intake (DMI) and 0.189 g/kg DMI for untreated and phytase-treated diets, respectively, and corresponding average Ca TTTD values for canola meal of 46.6% and 70.3%.
"Unless these endogenous losses are taken into account by using TTTD values during diet formulation, Ca digestibility will be underestimated and subsequently oversupplied," states Professor Stein. "The research has also demonstrated that TTTD values for Ca are not affected by the Ca level in the diet, indicating that the resulting figures would be additive in diet formulation calculations. The long term goal is to establish the requirement for digestible Ca for all groups of pigs," explains Caroline Gonzalez-Vega, a PhD candidate in Dr Stein's laboratory who has conducted much of the work on Ca digestibility. "By doing so, we will be able to formulate diets in the future based on the requirement for both digestible phosphorus and digestible calcium."
The next phase of the research is to establish Ca TTTD values for a wide range of commonly used plant- and animal-based feed ingredients.