Paws for thought
Scan the supermarket aisles and you'll see many products claiming to provide a complete diet for your cat, which is defined in the Australian pet food standard as a food that meets nutritive requirements set by the American Association of Feed Control Officials (AAFCO), the US animal feed industry body. We sent a selection of samples to a lab to see if manufacturers are meeting key nutritional claims.
Our expert testers
Testing cat food is complex and costly. We don't have the facilities at CHOICE to test cat food, so to analyse key nutrients we send samples to a lab accredited by the National Association of Testing Authorites (NATA). Our European counterparts helped advise us on the key nutrients to test, as did David Fraser, Emeritus Professor of animal science at Sydney University. They also looked over the raw data once it was returned from the lab.
After the results were examined, we spent a lot of time at CHOICE poring over and crunching the numbers to try to make meaningful comparisons with official guidelines.
How we choose what we test
The Australian pet food market is worth $1.85 billion, and wet cat food (that comes in tins and pouches) makes up the 'lion's share' of this (so to speak). So for our test we decided to focus on wet cat food varieties from major supermarket brands, as well as several samples sold at pet food retailers. We didn't focus on special cat foods only sold through vets, but we may look at this in future.
Which varieties to choose?
We can't cover the entire market, so we survey major manufacturers about current products in their range, and we select ones that are readily available on retail shelves. Our buyers then go and purchase them as a consumer would.
The lab requires a minimum amount of cat food for each sample. If we need to buy more than one sample of a particular variety to fulfill this requirement (because it only comes in small tins or pouches), we also check the packaging to make sure all samples come from the same batch.
How we test
Our lab analyses include:
- Crude protein, fat, fibre, carbohydrates and moisture using proximate analysis (a way to chemically determine the amount of common elements in food) as well as starch (not scored).
- Inorganic ash residue (minerals) which is produced after the material has been burnt at high temperatures. Higher levels suggest bone meal has been used. This is a good source of calcium and phosphorus, but it's also a cheap one.
- Taurine, an amino acid that prevents a number of health issues in cats, including blindness. Cats can't produce it themselves.
- Calcium. There is no published safe upper limit for cats available, but too much could reduce the ability for other essential minerals to be absorbed.
- Phosphorus. Another important element found in bone.
- Sodium. Encourages cats to drink water. A healthy adult cat should not have a problem with excreting high levels of salt.
- Magnesium. Small amounts are essential for general health, but too much could lead to struvite crystals in urine which could cause urethral obstruction.
- Metabolisable energy (ME). ME is the energy available to the animal from the food. It's determined using a special formula based on the proximate analysis. AAFCO guidelines assume that the cat food has an ME of 4000kcal per kg. If the energy density is more than around 4500kcal per kg, the cat will eat less of the food (as cats can largely self-regulate their energy intake) and therefore will need a higher concentration of nutrients. We've checked to see if nutrient levels of higher density foods are sufficient.
Test criteria explained
To score the cat food, we use guidelines issued by the American Association of Feed Control Officials (AAFCO). These guidelines, adopted by the Pet Food Industry Association of Australia (PFIAA), are "designed to establish practical minimum and some maximum nutrient concentrations for dog and cat foods".
Minimum guidelines are presented as a percentage of dry matter (after moisture is removed), as well as in grams per 1000kcal of ME. For more on the actual numbers, see our test of wet complete adult cat food.
AAFCO bases recommendations on a 2006 publication called Nutrient Requirements of Dogs and Cats, written by the US National Research Council (NRC). Europe's AAFCO-equivalent, the European Pet Food Industry Federation (FEDIAF), also uses the NRC as its source. There are minor differences between the US and European requirements, and while we focus on AAFCO guidelines, we also take FEDIAF recommendations into consideration.
Aspects we score and test include:
Calcium to phosphorus ratio (30% of overall score)
Not everything we test or score has an official AAFCO guideline.
A crucial part of our score is based on whether the cat food has a good balance of calcium and phosphorus (known as the Ca:P ratio).
These elements are essential for bone growth in growing kittens and should continue to be maintained at relative amounts throughout the cat's adult life. Our preferred ratios fall between 1:1 and 2:1, which echoes the European pet food industry requirement (FEDIAF). We define optimal ratios between 1.2:1 and 1.4:1.
Professor Fraser says ratios below 1:1 could, over time, cause "gradual loss of bone mineral and the possibility of bone fracture". Ratios above 2:1 could lead to a phosphorus deficiency, which could impact "not just on the maintenance of bone mineralisation but also on the function of many tissues and organs, as phosphorus has an integral function in many biochemical processes in all cells of the body".
Many samples we tested don't provide an ideal balance.
The PFIAA, along with other major manufacturers we spoke to including Coles, Safcol, Mars Petcare and Woolworths, disagree with how we have chosen to score products based on their Ca:P ratios. A ratio is not mentioned in the AAFCO publication (guidelines specify a minimum of 0.6% calcium in dry matter and 0.5% phosphorus, but there's no requirement for the relative proportion to be maintained). Manufacturers argue that so long as they meet minimum requirements of each separate mineral, then they are fulfilling the required nutritional guidelines.
PFIAA executive manager John Aird, on behalf of the industry, tells us: "AAFCO have chosen not to publish 'ideal' recommended Ca:P ratios for the cat perhaps reflecting the diverse nutritional research findings in studies exploring this topic. This may indicate that cats can adapt to a considerable range of Ca:P in their diet, providing the minimum amounts of each mineral are provided."
The good/bad points in our wet cat food test includes manufacturers' responses to our findings.
We still believe that a ratio of 1:1 to 2:1 is best.
Protein (15%) and fat (10% of overall score)
We check to see if these meet minimum guidelines.
Ash (10% of overall score)
Anything above more than around 11% of dry matter means a high percentage of bone meal is used to bulk up the food. While bone is a good source of calcium and phosphorus it's also a cheap one.
Minerals (20% of overall score)
We test calcium, phosphorus, magnesium and sodium levels to see if they meet minimum requirements. There isn't enough evidence about toxic concentrations, but some studies show that an excess of some minerals such as calcium and magnesium could have an adverse effect.
Taurine (15% of overall score)
We check to see whether the food meets minimum taurine requirements.