FEED ADDITIVES ▶▶▶
Counteracting the anti-nutritional effects of calcium
Calcium and phosphorous are two vital minerals for animal development and function. However, animal feeds are often over-supplemented with calcium, which negatively affects the activity of phytase and the availability of phosphorous. This can be overcome by supplementing the right phytase.
BY DR ARNO DE KREIJ, DANISCO ANIMAL NUTRITION (IFF) C Weight of
precipitate (% total)
14 12 10 8 6 4 2 0
0 Axtra®
Phytate bound calcium
(120mins) Average value for all samples at T=0 (except buffer) 30 ▶ ALL ABOUT FEED | Volume 29, No. 7, 2021 PHY GOLD 20 40
Hybrid phytase
60 E. coli phytase 80
E. coli 2 phytase
100
Citrobacter phytase
E. coli 3 phytase
alcium and phosphorous are crucial for growth, bone formation, muscle contraction, energy metabolism, reproduction, and immunity. Deficiencies in either mineral may directly limit growth performance and
optimal bone development, ultimately leading to animal morbidity and mortality. To meet calcium and phosphorous requirements, these are supplemented in feed formulas. However, over-supplementation can result in homeostatic imbalance and improper bone development. Understanding
Figure 1 - In vitro hydrolysis of calcium-phytate complexes by different phytases after 15-, 30-, 60-, and 120-minutes incubation at pH 2.5 followed by precipitation at pH 6.5.
Buffer
the mechanisms of action of calcium and phosphorous and their interrelationship are, therefore, crucial to assessing feed formulation requirements, adjusting supplementation levels, and preventing the anti-nutritional effects of both minerals.
Calcium: the hidden anti-nutrient Calcium is usually the mineral with the highest concentration in feed formulas. It is present in high amounts to ensure mini- mum requirements, but also because calcium sources are inex- pensive and calcium excretion does not represent an environ- mental threat. However, high calcium levels can decrease the availability of other nutrients, including phosphorous (supple- mented as phytate-phosphorous). Calcium facilitates the bind- ing of phytate to proteins in the gut, including digestive pro- teases (e.g. pepsin and trypsin) aggravating the anti-nutritional effects of phytate. These protein-phytate complexes are insolu- ble and poorly accessible to both proteolytic enzymes and phytase – the enzyme that degrades phytate in the gut. Excess calcium, therefore, reduces protein availability and digestibili- ty, protein solubility, and phosphorous availability. In abun- dance, calcium also forms precipitates with fatty acids, thus re- ducing dietary energy digestibility and phytate absorption. Although calcium has low affinity for phytate, its excess leads to the formation of insoluble calcium-phytate complexes in the small intestine, which are phytase-resistant. Thus, phytate be- comes inaccessible for hydrolysis and the availability of both phytate-phosphorous and calcium is significantly reduced.
Axtra® PHY GOLD
Time (min) 120
E. coli 4 phytase
Not all calcium looks alike Limestone is the primary source of dietary calcium in broil- ers, sometimes contributing to over 50% of the total feed. Limestone is readily available on the market, has a consistent calcium concentration, contains minor concentrations of pol- lutants, and it is cheap. Nevertheless, limestone’s acid-bind- ing capacity increases the pH along the gut, which reduces phytate’s solubility and its accessibility to phytase, allowing calcium to form insoluble complexes with phytate. Moreover, the calcium in limestone may directly inhibit phytase activity by competing for the active sites of the enzyme. Calcium concentration in the gut and its potential to bind
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