Calcium has a profound affect on phosphorous digestibility, explained Dr. Roselina Angel, professor in the Department of Animal and Avian Sciences at the University of Maryland during a webinar, How calcium and phosphorus optimize broiler performance, presented by WATT Global Media on November 29. “Most people do not pay enough attention to limestone, their primary source of calcium in monogastric diets; limestone is the primary culprit because it becomes very soluble very quickly,” Angel said.

Angel went on to explain that calcium has its profound negative effects on phosphorous digestibility mainly through interactions with phytic acid. However, this is not always the only negative effect; phytic acid and calcium interactions are saturable, though depending on phytic acid concentrations and soluble calcium concentrations. “Phytate concentration matters,” said Angel. Phytate concentration levels vary depending on where you are in the world and how much phytase is in your diet.

"Effect of calcium on phytase efficacy differs between phytase sources." – Yueming Dersjant-Li

“The impact of calcium particle size differs among phytases,” said Dr. Yueming Dersjant-Li, senior scientist with the Global Innovation group within the Danisco Animal Nutrition team, which is a part of Dupont Industrial Biosciences. Li added that fast-acting phytase reduces calcium phytase complex more efficiently and increases more soluble calcium than phosphorous.

According to Li, a study showed that when using fast-acting phytase, soluble calcium compared to phosphorous released at a rate of 1.27 grams of calcium to 1 gram of phosphorous after 30 minutes. “Not using calcium contribution, or using low calcium contribution values, can cause a calcium phosphorous imbalance to the birds,” Li noted.

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The source of phytase matters as well. “From literature we know it is important, but we have not quantified, and we are in the process of trying to do that,” Angel explained. Li agreed, “Effect of calcium on phytase efficacy differs between phytase sources,” she said.

Limestone in broiler feed management

Limestone is one of the main feed tools that producers can change. “I hope producers look at their limestone particle size and solubility, because you can do a lot with your cheapest ingredient to actually achieve better phosphorous digestibility,” Angel said. This should allow producers to get a lot more out of their phytase. By maximizing phytase use, producers are ultimately getting the most they can out of their limestone by increasing phosphorus digestibility.

“The optimal calcium matrix is related to dietary calcium level, limestone particle size and solubility, and calcium phosphorous ratio,” Li concluded.