For these reasons, the best way to compare phosphorus levels is to use the measure of actual phosphorus content in milligrams per 100 kilocalories. This equalizes the high-calorie and low-calorie foods. (Note, a kilocalorie or kcal is the unit that most of us layfolk refer to simply as "calorie".) Some dog food companies use the figure of phosphorus in grams per 1000kcals, but that is easy to convert into mg/100kcal.

While phosphorus in mg per 100kcal makes the comparison between foods simple, it's not a common measure that most consumers request, so it's not listed on dog food bags and many companies don't even have that information available. It can be calculated from other figures that are reasonably easy to get: the dry matter basis phosphorus percentage and the calories per kilogram. For those brands that do not make the 'dry matter basis' figures available to consumers, you can calculate that information from the phosphorus percentage as fed, the calories per kilo, and the moisture content. Some companies will provide you with the actual moisture content as found in laboratory analysis - otherwise a maximum moisture content figure is usually given on the bag or can. The maximum moisture listed is going to be slightly higher than the actual moisture content of the food, but it's not that far off.

I compiled the figures for phosphorus as well as some other figures for general nutrition for various dog foods. If you want to know why some brands are included and others not, one of the main criteria were how easy it was to obtain the figures. For example, Nestle/Purina customer support was excellent and easily available from a toll-free phone number. They had all the figures I wanted immediately available. Similarly, Natura, the company that makes California Natural and some other lines of food emailed me a comprehensive spreadsheet for their foods.

By contrast, some of the brands had customer support folks seemed peevish that I wanted so much information or simply did not have these figures available. I emailed a few of the smaller brands, when the front-line support techs could not supply the figure of phosphorus per 100kcals, but I did not receive answers, even from Canidae, a company that has an staff nutritionist. In a few cases, such as that of "Sensible Choice" the information on the manufacturer's website differed from that given by the support staff, and the phosphorus amount per 100g were not available at all.

The following chart has the phosphorus content in mg/100kcal for those brands that provided that figure. The dry matter basis phosphorus percentage is also included for comparison, as well as figures for DMB protein, fat, and the caloric content, which is the Metabolizable Energy in kcals per gram, as measured in dry matter basis.

The dry matter basis figures were provided by the manufacturers in all cases except for that of Pedigree - they didn't have DMB figures available, so I calculated that using the maximum moisture listed on the bag.

Food	phosphorus mg per 100kcal	% phos. minimum DMB	% protein DMB	% fat DMB	Metabolizable Energy kcal/gram	AAFCO "Life Stage" Designation
K/D (Hills Veterinary Diet)	55	.24	14.9	19		Maintenance
Diamond Low-Fat/Senior	140	.50	18.4	9.3		Maintenance
Science Diet Senior	144	.58	19.5	15.4		Maintenance
Science Diet Maintenance Chicken and Rice	148	.60	23.3	14.8		Maintenance
Science Diet Maintenance Beef	154	.62	23.3	14.8		Maintenance
Science Diet Maintenance Original	159	.64	24.7	15.8		Maintenance
Science Diet Adult Large Breed Maintenance	165	.66	23.86	14.43		Maintenance
Science Diet Adult Light	170	.56	24.4	8.9		Maintenance
Science Diet Maintenance Lamb Meal and Rice	184	.74	22.8	15.9	4.01
Innova Senior	186	.72	19.89	8.84	3.49	Maintence
Eukanuba Adult Maintenance (and Adult Small Bite)	196	.92	26.2	16.9	4.33	All Life Stages
Pro Plan Adult Lamb and Rice	197	.89	28.99	19.44	4.59	Maintenance
Eukanuba Adult Large Breed	202	.85	25.19	14.41	3.92	Maintenance
Pro Plan Performance	202	.97	34.48	23.56	4.82	All Life Stages
Purina ONE Chicken and Rice	205	.95	31.85	19.25	4.62	All Life Stages
Eukanuba Adult Premium Performance	207	1.00	31.4	21.2	4.45	All Life Stages
Iams Large Breed Adult Maintenance	208	.91	24.31	14.07	4.03	All Life Stages
Diamond Premium Adult Maintenance	210	.90	29.4	20.2		All Life Stages
Iams Active Maturity (Senior)	213	.90	25.31	11	3.89
Purina ONE Beef and Rice	216	.98	29.96	19.9	4.54	All Life Stages
Eukanuba Senior Maintenance	218	.95	26.98	11.78	3.99	Maintenance
Eukanuba Senior Large Breed	221	.87	26.98	11.78	3.93	Maintenance
Pro Plan Adult Chicken and Rice	221	1.01	28.52	20.38	4.56	Maintenance
Iams Puppy	224	1.04	32.07	19.87	4..29
Nutro Natural Choice Senior	227	.88 [max. 1.1]	23.23	12.7	3.88	Maintenance
Nutro Natural Choice Large Breed Weight Management	228	.85 [max. 1.4]	21.25	9.94	3.74	Maintenance
Pro Plan Reduced Calorie	228	.91	28.26	9.43	3.98	Maintenance
Science Diet Large Breed Puppy	229	.84	30	10.7	3.41
Pedigree Mealtime with Lamb and Rice	230		25.00	13.63		All Life Stages
Pro Plan Adult Beef and Rice	230	1.01	30.44	18.78	4.51	Maintenance
Pro Plan Senior	233	.95	31.23	14.77	4.08	Maintenance
Purina ONE Lamb and Rice	235	1.09	30.49	20.15	4.66	All Life Stages
Nutro Natural Choice Large Breed Puppy	235	.94	31.8	15.94		Growth and Maintenance
Innova Dog	239	1.10	26.52	15.47	4.17	All Life Stages
Pro Plan Puppy Chicken and Rice	239	1.11	31.62	21.23		All Life Stages
Purina Dog Chow	240	.90	23.38	12.97	4.00	All Life Stages
Nutro Max Weight Control Formula	241	.91	18.80	10.69	3.78	Maintenance
Pro Plan Puppy Lamb and Rice	243	1.11	31.26	21.63		All Life Stages
Pro Plan Adult Turkey and Barley	245	1.05	27.92	18.34	4.28	Maintenance
Purina ONE Reduced Calorie	246	.95	28.63	9.61	3.87	Maintenance
Pro Plan Puppy Beef and Rice	247	1.11	31.21	20.60		All Life Stages
Iams Chunks (same as Mini-Chunks)	249	1.10	27.41	16	4.06
Diamond Maintenance	250	1.00	23.9	13.7		All Life Stages
Diamond Professional Formula	250	1.10	34.1	23.4		All Life Stages
Diamond Puppy	250	1.10	35.3	23.4		All Life Stages
Purina Dog Chow Little Bites	250	.95	22.37	12.27	3.77	All Life Stages
California Natural Lamb Meal & Rice	252	1.12	24.07	12.49	3.99	All Life Stages
Nutro Natural Choice Large Breed Adult	255	.70 [max 1.40]	30.2	14.98	3.97	Maintenance
Nutro Natural Choice Large Breed Senior	255	[max 1.0]	25.38	14.3	3.93	All Life Stages
Pedigree Puppy	260	1.02	30.86	11.36
Purina Fit and Trim	260	.83	28.38	6.49	3.10	Maintenance
Purina Hi-Pro	260	1.15	29.54	17.62	4.26	All Life Stages
Purina Puppy Chow Large Breed	260	1.02	30.19	13.93		Growth and Maintenance
Nature's Recipe Allergy - Vegetarian	266	.98	20.73	9.70	3.69	Maintenance
Purina Dog Chow Senior 7 Plus	270	.99	27.83	11.28	3.63	Maintenance
Purina Puppy Chow	270	1.08	29.95	15.55		Growth and Maintenance
Purina ONE Large Breed Puppy Formula	273	1.08	34.47	11.67	3.97	Growth and Maintenance
Nutro Natural Choice High Energy	277	1.20	34.48	22.64	4.53	All Life Stages
Diamond Lamb and Rice Puppy	280	1.10	30.3	16.5		All Life Stages
California Natural Reduced Calorie	286	1.10	19.69	8.84	3.49
Purina ONE Puppy Formula	287	1.33	31.12	20.66	4.64	All Life Stages
Nature's Recipe Easy to Digest Chicken Oat & Barley	288	1.17	28.24	17.18	4.05
Science Diet Puppy	297	1.22	29.4	19.4
Nature's Recipe Senior Lamb Meal & Rice	298	.89	17.05	9.14	2.97
Innova Puppy	300	1.55	28.73	13.26	4.00	All Life Stages
Purina Beneful	300	1.20	28.89	13.95	3.97	All Life Stages
Diamond Lamb Meal and Rice Adult	310	1.20	26.2	15.7		Growth and Maintenance
Come and Get It	313	1.17	24.2	13.30	3.43
Nutro Max Puppy	315	1.31	31.41	19.23	4.15	All Life Stages
Nutro Max Adult	325	1.31	29.77	18.05	4.02	All Life Stages
Nutro Max Mini Chunk	325	1.31	29.77	18.05	4.02	All Life Stages
Nutro Max Natural	325	1.31	29.77	18.05	4.02	All Life Stages
Nutro Natural Choice Chicken Meal and Rice	339	1.31	24.28	14.54		All Life Stages
Nature's Recipe Joint & Hip Formula	344	1.29	23.37	13.37	3.75
Nutro Natural Choice Lite	355	1.21	17.17	7.09	3.40	Maintenance
Alpo Lamb Meal Rice and Barley	357	1.21	23.68	15.1	3.59	All Life Stages
Alpo Puppy	361	1.21	31.7	13.6	3.64	Growth
Nature's Recipe Adult Lamb Meal & Rice	364	1.38	23.55	13.65	3.78
Pedigree Large Crunchy Bites (also Small Crunchy Bites)	370		23.86	9.09
Alpo Beef and Chicken	372	1.24	22.47	12.12	3.35	All Life Stages
Nutro Natural Choice Dental Care Adult	396	1.46	23.27	14.3	3.70	All Life Stages
Nutro Natural Choice Puppy	403	1.40	29.49	14.31	3.78	All Life Stages
Nutro Natural Choice Lamb Meal and Rice	406	1.53	24.47	14.39		All Life Stages
Pedigree Meaty Chunks with Rice and Vegetables	420	1.59	23.86	9.09
Nature's Recipe Easy to Digest Lamb, Rice & Barley	423	1.56	25.37	11.93	3.69
Nutro Premium Nutrition Dog Food	425	1.58	29.97	14.41		All Life Stages
Nature's Recipe Venison Meal and Rice	429	1.6	25.08	12.82	3.72
Nature's Recipe Puppy	470	1.80	25.86	28.26
Nature's Recipe Puppy Lamb Meal & Rice	470	1.8	28.26	16.73	3.84

The figures in the above table were collected in March 2002 and the Natura figures were revised in April 2003 when more detailed data was provided.

The Hills Prescription Diet food k/d, designed for dogs with chronic renal failure or other kidney problems is included simply as a reference level. I am not recommending that anyone feed k/d to a dog who has not been diagnosed with renal failure.

Here are some links that might be useful:

• Guidelines for comparing pet diets, from the Ohio State Veterinary Hospital Nutrition Support Service:
  http://nss.vet.ohio-state.edu/Vdm/vetdietmanual.html
• FDA's Center for Veterinary Medicine's page on "Interpreting Pet Food Labels - Special Use Foods" http://www.fda.gov/cvm/index/consumer/labelint.htm
• Washington State University College of Veterinary Medicine has a chart: "Canine Diets to Impact Kidney and Urinary System Health at:
  http://www.vetmed.wsu.edu/Boeing/small_animal_medicine/urolith.htm
• Washington State University's page on Chronic Renal Failure:
  http://www.vetmed.wsu.edu/boeing/small_animal_medicine/crf.htm
• Article, "Feeding the Older Dog" on Speedyvet site discussing protein/phosphorus intake for older dogs:
  http://www.speedyvet.com/NIP/olddogs/default.htm

This topic and canine nutrition in general has been discussed on the VETMED mailing list, a moderated discussion list on veterinary and animal health topics.