Selecting the right combination of ingredients and additives to obtain the right amount of phosphorus in the preparation of pet food (especially staple food) is a complex task.There has been literature on secondary sampling and phosphorus analyses of commercially available products, and both under- and over-phosphorus levels have been found to co-exist.From a nutritional control point of view, the incidence of this situation should be higher than that detected by sampling; and from a dietary point of view, the complexity and difficulty of controlling phosphorus levels arises from the nature of the phosphorus prevalent in food, the variation in concentration, the differences in bioavailability and the utilisation of phosphate additives commonly used to improve the process.
Role of phosphorus
Phosphorus has a unique utility in metabolism.It is involved in bone structure, DNA, RNA, membrane phospholipids, phosphoproteins, high-energy phosphate bonds (e.g., ATP), and acid-base balance, and plays a key role in nutrition and health.
Phosphorus deficiency can lead to abnormal bone development and a host of other health problems in puppies and kittens.It can affect yin and yang ion balance and urinary health through stone (urolith) formation; it has also been linked to chronic kidney disease in cats (renal failure), the incidence of which increases with the age of the animal, and restricting phosphorus in the diet is important to manage the condition.
Phosphorus and calcium are inextricably linked through the operation of vitamin D/parathyroid hormone, and thus the discussion of phosphorus nutrition is complicated by metabolic pathways, endocrine regulation of calcium and phosphorus absorption, circulation, and excretion.
Phosphorus in pet food
Meat meal provides the largest proportion (40-70%) of phosphorus in a pet diet based on dry food, with most coming from bone and a small amount from dried chicken tissue, and this type of phosphorus is highly bioavailable.
The contribution of carbohydrates to total phosphorus is about 20 to 35 per cent, most of which is in the form of phytate phosphorus and therefore less bioavailable.
Subsequent phosphorus is essentially derived from additive phosphorus sources, which may be added to meet minimum nutrient requirement standards or to improve processes, mostly with a stacking or dual effect.Depending on the chemical composition, there are more than 60 different phosphorus salts that can be used as food additives with different roles.They can be used as PH regulators for acidification, alkalisation or as buffers; they can act as adsorbents, coagulants and chelating agents or, conversely, as anticoagulants, emulsifiers and flow agents; and some are used as leavening agents and protein regulators.On a proportional basis, they can contribute more than 30% of the phosphorus in pet food formulations.
Common sources of phosphorus used as nutritional fortification ingredients in pet foods are monocalcium, dicalcium and tricalcium phosphate and monosodium phosphate, with sodium tripolyphosphate and sodium hexametaphosphate occasionally used.Phosphoric acid is the most commonly added ingredient from a process enhancement perspective, due to its antimicrobial properties, and is particularly commonly used in liquid food attractants; sodium pyrophosphate is also a common cat product attractant.
Difficulties in controlling phosphorus levels in pet food formulations
As phosphorus is present in most food ingredients, especially bone, it is common for phosphorus to be supplied in diets in excess of standard or organismal requirements, especially for high protein staples.Most high protein staple food ingredients contain a large proportion of melted protein (meat meal) and correspondingly high levels of bone meal.
To complicate matters further, phosphorus utilisation rates vary from one source to another.The weak acid solubility of phosphorus in cereals (as a rough indicator of utilisation) is between 40 and 60 per cent, in vegetable protein concentrates it is less than 25 per cent, in meat powders it is between 20 and 60 per cent, and in raw and cooked meats it is between 30 and 80 per cent.
As a corollary, pet foods containing these ingredients have a phosphorus utilisation rate of about 60 to 80 per cent, which is confirmed by animal experiments: postprandial fluctuating levels of blood phosphorus levels in animals are at levels consistent with this, and increased solubility of the phosphorus source results in increased absorption.The situation is further complicated by the calcium-phosphorus ratio: i.e. phosphorus absorption is high when the calcium-phosphorus ratio is low and vice versa.
This means that phosphorus control is not an easy task.The largest proportion of dietary sources of phosphorus is probably meat meal, and lowering its phosphorus content is difficult; it becomes higher in high-protein (and therefore high-ash and phosphorus) foods.
Managing dietary protein sources can help control phosphorus levels.One approach is to dilute phosphorus by using boneless frozen or spray-dried meat.Another is to partially replace animal protein with plant protein.Plant proteins are lower in phosphorus and have lower phosphorus bioavailability due to phytates.However, if a significant proportion of phosphorus is derived from plant proteins, phosphate supplementation or addition of phytase may be required to supplement the phosphorus deficiency.In addition, it may be helpful to use substitutes for food technology functional phosphates or to ensure that they are considered in the total formulation.It may also be helpful to control phosphorus levels by using substitutes for acid salt products that need to be added in the original preparation process or by ensuring that this type of phosphorus content is included in the total phosphorus calculation.
Clearly, there are ways, but they require thoughtful management and ongoing evaluation to ensure that the finished food meets the standard requirements as well as the needs of the animals themselves.
