Calcium and phosphorous are components of hydroxyapatite, which is the primary structural mineral in bone. Cartilage forms the organic matrix of bone which is later mineralized with hydroxyapatite.
Dr. Douglas R. Korver, professor, University of Alberta, said that broilers have immature bones at today's market ages of six weeks or less. Speaking at the WATTAgNet.com webinar, Optimizing calcium/phosphorous contribution and skeletal integrity through phytase use in broiler diets, Korver said that recent genetic improvements have resulted in faster growing strains that don't have as many of the metabolic and structural issues as broilers had in the 1990s. But, this doesn't mean today's broilers can't have skeletal issues.
Rapid growth and porous bones
The immature bones of broilers tend to be porous, according to Korver, because the bones haven't been fully mineralized. The porosity of the bones can lead to some breakage issues when the birds are processed, and it can also cause what he characterized as "black bone syndrome." When bone-in-chicken is frozen, the bone marrow expands and can be forced out of the bone through the pores in the bone where the marrow can stain the meat. The meat then looks "black" around the bone when it is cooked.
The rapid growth rate of modern broilers pushes the birds closer to the physiological limits of bone formation and this makes feeding calcium and phosphorous at the appropriate levels even more important than it has been in the past, Korver reported. Because producers are now counting on the phytate phosphorous in feed ingredients as a major source of phosphorous for broilers and layers, it is important to make sure you are adding the right amount of phytase enzyme to the diet.
Phytase enzymes break down the phytate molecules in feedstuffs and make the phosphorous available for the bird to use, but it isn't quite as simple as it sounds, according to Dr. Peter Plumstead, associate professor, University of Pretoria. He said that there are a number of phytase products on the market and they don't all have the same activity levels at different pHs. Feed has a residency time of 40 to 60 minutes in the proventriculus and gizzard of a broiler, where the pH is 2.5. Because of this, Plumstead said that you want a phytase that works rapidly at a low pH in broilers to make as much of the phytate phosphorus available to the bird.
Plumstead shared data on factors affecting the availability of phytate phosphorous with phytase addition to the diet and he said that it is important to know the phytate concentration in the feedstuffs used to formulate the diet. Korver said that new imaging technologies allow for bone development in individual birds to be tracked over time. Older measures like bone breaking strength and bone ash weights required the bird be sacrificed to take the measurements. He said that the new techniques will help provide insight on how dietary changes affect bone development.
Plumstead said that adding phytase to the diet reduces the amount of inorganic phosphorous that must be added to the diet, which saves money and it reduces the amount of phosphorous in the litter. Some producers are successfully using higher phytase concentrations in diets, and this can be good for the environment and the bottom line.