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Ingredient file // Vitamin or mineral

Iron Sulfate

An absorbable iron source for measured gaps

Iron sulfate is a mineral salt added when a recipe needs more iron than its other ingredients supply. Dogs absorb iron from ferrous sulfate, but adding it to a diet that already has enough iron has not shown a blood benefit.

Role in the food Supporting nutrient
What it is
A concentrated iron salt used in small amounts to adjust the iron content of dog food.
Made from
Iron or iron oxide and sulfuric acid
Main job
Adds dietary iron
Typical amount
Not published
Watch for
Separate iron supplements within a dog's reach
Not the same as
Iron oxide

Straight answer

Is Iron Sulfate safe for dogs?

Read it as a small mineral adjustment

Look for iron sulfate among the mineral and vitamin additions, below the main meat, starch and fat. Its position fits a trace mineral's job, but the list cannot tell you the food's iron level. Check the nutritional adequacy statement for your dog's life stage and keep separate iron supplements out of reach.

Why it is in the food
Adds dietary iron

Our read // In our catalog

In 1 of every 87 foods we track

Share of foods that list it

1%

37 of the 3,204 foods with an ingredient list on file, from 12 brands. 18 dry dog food, 17 wet dog food, 2 dog food topper.

Each square is 1% of the catalog

Where it sits on the label

Median position 18. In the top five of 0 foods, so it is usually a minor ingredient.

Top five List position, heaviest first

Above the salt

28%

Usually listed after the salt, which caps it at roughly 1% of the recipe in 72% of foods.

Price per lb

Foods with it $2.42
All foods $3.25

Median of the cheapest bag price across 14 priced foods, 26% below the catalog. The price is the food's, not the ingredient's.

Who leans on it

19%

of the foods that list it are from Evanger's. 12 brands use it in total.

What it is

How it is made

Steel processors use acid to remove surface oxides. When they use sulfuric acid, the spent liquid contains ferrous sulfate. Suppliers recover crystals from that liquid, which has historically supplied animal feed as well as fertilizer.5,6

  1. 01 // Source Steel and acid Steel with surface oxides enters a sulfuric acid bath during cleaning.
  2. 02 // Process Iron dissolves Surface oxides and some underlying iron react with the acid, forming dissolved ferrous sulfate.
  3. 03 // Process Crystals recovered The spent liquid is filtered, and ferrous sulfate is crystallized from it.
  4. 04 // Process Crystals dried Drying moist crystals produces forms with different water content and different iron concentrations.
  5. 05 // Output Ferrous sulfate The dried salt reaches feed makers as a concentrated mineral ingredient.

What is in it

Composition, dry matter

33

% iron

The reference value for dry ferrous sulfate monohydrate. Commercial material contains less, so its hydrate form matters when a recipe is measured.

Iron 330,000 mg/kg3
Sulfur 189 g/kg3
Ash 100%3
Crude protein 0%3

These are reference values for monohydrate, not a guaranteed batch analysis. Commercial dried monohydrate contains 29 to 31% iron; dried heptahydrate contains 19.5 to 20.5%.3,6

Why it is in the bag

A small iron top-up, not filler

  1. Main nutrition
  2. Supporting nutrient
  3. Does a job
  4. Mostly filler

Makers add ferrous sulfate so the finished food meets its iron target. The dry salt is about 33% iron, so a tiny weight does the job, and since labels rank ingredients by weight it often sits low on the list. It is not filler. In a 22-dog trial, a base diet with 115 mg/kg natural iron showed no measurable blood difference with or without 80 mg/kg added.2,3,7

  1. 01

    Closes iron gaps

    Meat and plant ingredients contribute iron. Formulators add ferrous sulfate when those ingredients do not supply enough for the finished food's iron target.2,4

  2. 02

    Fits small additions

    Dry monohydrate has a high iron concentration, so a recipe can adjust its iron content without adding much ingredient weight.3

  3. 03

    Uses industrial supply

    Steel processing produces ferrous sulfate as a co-product at industrial scale. Animal feed has historically been a primary use for the recovered salt.5

How much A dog feeding trial tested added ferrous sulfate at 80 mg of iron per kg of dry diet, layered on top of an already iron-adequate base diet.2

Our read // The claims

What the evidence supports

Strong: controlled studies in dogs agree. Some: small or mixed dog data. Thin: mechanism or lab work only. None: nothing, or the evidence points the other way.

  1. Brands say

    Dogs absorb iron from iron sulfate

    Evidence

    1. Strong
    2. Some
    3. Thin
    4. None

    An adult dog isotope study measured absorption using ferrous sulfate as its comparison source at iron-equivalent doses of 1.5 and 15 mg. That shows uptake, but does not show a blood benefit from adding it to an iron-adequate kibble.1,2

  2. Brands say

    Chelated iron is always better absorbed

    Outruns the evidence

    Evidence

    1. Strong
    2. Some
    3. Thin
    4. None

    A cultured human intestinal cell study moved more glycine-bound iron than ferrous sulfate across its cell layer. It did not feed dogs or measure absorption from complete dog food, so it cannot justify an always-better claim.9

  3. Brands say

    Added iron improves healthy dogs' blood

    Outruns the evidence

    Evidence

    1. Strong
    2. Some
    3. Thin
    4. None

    In a 22-dog trial lasting 26 weeks, blood measures did not differ between an iron-adequate diet with and without added ferrous sulfate. The trial did not measure uptake of the added iron; it found no added blood benefit in that recipe.2

  4. Critics say

    Iron sulfate in kibble is poisonous

    Outruns the evidence

    Evidence

    1. Strong
    2. Some
    3. Thin
    4. None

    Dogs in the feeding trial had normal blood measures with 80 mg/kg added iron. Pet Poison Helpline describes poisoning after pets swallow concentrated iron products. A measured addition to food is a different exposure.2,8

  5. Critics say

    Iron sulfate is just cheap filler

    Outruns the evidence

    Evidence

    1. Strong
    2. Some
    3. Thin
    4. None

    The dry monohydrate reference is 33% iron and has no crude protein. Its job is to adjust a trace mineral, not bulk up the food or raise its protein figure.3

Straight answers

What owners ask

  1. Q01

    Is it just filler?

    No

    It supplies iron in a small addition. The dry monohydrate reference is about 33% iron, with no crude protein. It adjusts the mineral content rather than bulking up the recipe.3

  2. Q02

    Why is it near the end?

    Small addition

    Iron is a trace mineral, so an added iron salt belongs below the main food ingredients. Labels rank ingredients by weight but do not disclose how much iron the finished food contains.4,7

  3. Q03

    Does my dog need extra iron?

    Not routinely

    A 22-dog trial found no blood advantage from added ferrous sulfate when the base diet already supplied enough iron. The relevant question is whether the complete food meets your dog's nutritional needs, not whether its ingredient list names an iron salt.2,7

Who uses it

Brands, best sellers and the company it keeps

Top brands, by foods that list it

  1. Evanger's 7 / 30
  2. Zignature 7 / 46
  3. Nulo 7 / 117
  4. Abound 4 / 20
  5. Ol' Roy 3 / 6
  6. Canidae 3 / 35
  7. Pure Balance 1 / 17
  8. Kismet 1 / 3
  9. Halo 1 / 41
  10. Cesar 1 / 45

Foods that list it / all the brand's recipes we track.

Plus 2 more brands.

Usually listed with, share of the foods that list it

  1. Mixed Tocopherols 49%
  2. Chicken Fat 43%
  3. Peas 35%
  4. Lamb 35%
  5. Brown Rice 32%
  6. Chicken 30%
  7. Zinc Sulfate 27%
  8. Guar Gum 27%
  9. Flaxseed 24%
  10. Natural Flavor 24%
  11. Thiamine Mononitrate 24%
  12. Minerals 24%

On the shelf

Foods that list Iron Sulfate

37 foods in our catalog list it, highest on the label first.

Evanger’s Super Premium Heritage Classic Chicken & Rice Dog Food TopperEvanger'sEvanger’s Super Premium Heritage Classic Chicken & Rice Dog Food TopperTopper // No. 6 on the labelKismet Shakers Daily Multivitamin Formula Freeze-Dried Chicken Recipe Dog Food TopperKismetKismet Shakers Daily Multivitamin Formula Freeze-Dried Chicken Recipe Dog Food TopperTopper // No. 7 on the labelEvanger’s Heritage Classic Lamb & Rice Dinner Wet Dog FoodEvanger'sEvanger’s Heritage Classic Lamb & Rice Dinner Wet Dog FoodWet // No. 7 on the labelZignature Essence LIR Landfowl Recipe Food Can Grain-Free Wet Dog FoodZignatureZignature Essence LIR Landfowl Recipe Food Can Grain-Free Wet Dog FoodWet // No. 7 on the labelZignature Essence LIR Ranch Recipe Food Can Grain-Free Wet Dog FoodZignatureZignature Essence LIR Ranch Recipe Food Can Grain-Free Wet Dog FoodWet // No. 7 on the labelZignature Original Food Turkey Formula Grain-Free Wet Dog FoodZignatureZignature Original Food Turkey Formula Grain-Free Wet Dog FoodWet // No. 8 on the labelZignature Original Food Kangaroo Formula Grain-Free Wet Dog FoodZignatureZignature Original Food Kangaroo Formula Grain-Free Wet Dog FoodWet // No. 9 on the labelOl’ Roy High Protein with Red Meat for Adult Dogs Dry Dog FoodOl' RoyOl’ Roy High Protein with Red Meat for Adult Dogs Dry Dog FoodDry // No. 13 on the labelOl’ Roy Complete Nutrition Small Bites Complete Nutrition Chicken and Rice Flavor Dry Dog FoodOl' RoyOl’ Roy Complete Nutrition Small Bites Complete Nutrition Chicken and Rice Flavor Dry Dog FoodDry // No. 14 on the labelHalo Holistic Vegan Plant-Based with Kelp Recipe Adult Dry Dog FoodHaloHalo Holistic Vegan Plant-Based with Kelp Recipe Adult Dry Dog FoodDry // No. 15 on the labelOl’ Roy Puppy Complete Chicken and Oatmeal Flavor Dry Dog FoodOl' RoyOl’ Roy Puppy Complete Chicken and Oatmeal Flavor Dry Dog FoodDry // No. 15 on the labelCanidae Pure, Lamb, Turkey & Chicken Grain Free Recipe Wet Dog FoodCanidaeCanidae Pure, Lamb, Turkey & Chicken Grain Free Recipe Wet Dog FoodWet // No. 16 on the label
Show 25 more
Evanger’s Heritage Classic Senior & Weight Management Wet Dog FoodEvanger'sEvanger’s Heritage Classic Senior & Weight Management Wet Dog FoodWet // No. 8 on the labelZignature Original Food Lamb Formula Grain-Free Wet Dog FoodZignatureZignature Original Food Lamb Formula Grain-Free Wet Dog FoodWet // No. 9 on the labelZignature Original Food Puppy Formula Grain-Free Wet Dog FoodZignatureZignature Original Food Puppy Formula Grain-Free Wet Dog FoodWet // No. 9 on the labelZignature Original Food Zssential Formula Grain-Free Wet Dog FoodZignatureZignature Original Food Zssential Formula Grain-Free Wet Dog FoodWet // No. 11 on the labelCanidae All Life Stages, Multi-Protein Chicken, Lamb and Fish Wet Dog FoodCanidaeCanidae All Life Stages, Multi-Protein Chicken, Lamb and Fish Wet Dog FoodWet // No. 17 on the labelCanidae All Life Stages, Lamb & Rice Recipe Wet Dog FoodCanidaeCanidae All Life Stages, Lamb & Rice Recipe Wet Dog FoodWet // No. 17 on the labelAuthority Everyday Health Large Breed Puppy Dry Dog FoodAuthorityAuthority Everyday Health Large Breed Puppy Dry Dog FoodDry // No. 18 on the labelEvanger’s Grain Free Duck & Sweet Potato Dinner Wet Dog FoodEvanger'sEvanger’s Grain Free Duck & Sweet Potato Dinner Wet Dog FoodWet // No. 19 on the labelEvanger’s Organic Turkey with Potato & Carrots Dinner for Dogs Grain-Free Wet Dog FoodEvanger'sEvanger’s Organic Turkey with Potato & Carrots Dinner for Dogs Grain-Free Wet Dog FoodWet // No. 20 on the labelEvanger’s Super Premium Lamb & Rice Dinner Wet Dog FoodEvanger'sEvanger’s Super Premium Lamb & Rice Dinner Wet Dog FoodWet // No. 21 on the labelEvanger’s Super Premium Beef Dinner for Dogs Grain-Free Wet Dog FoodEvanger'sEvanger’s Super Premium Beef Dinner for Dogs Grain-Free Wet Dog FoodWet // No. 21 on the labelNulo Culinary Harvest Puppy Chicken & Whitefish Recipe Dry Dog FoodNuloNulo Culinary Harvest Puppy Chicken & Whitefish Recipe Dry Dog FoodDry // No. 23 on the labelNulo Culinary Harvest Chicken & Whitefish Recipe Dry Dog FoodNuloNulo Culinary Harvest Chicken & Whitefish Recipe Dry Dog FoodDry // No. 23 on the labelCesar Puppy Filets in Gravy Puppy Food, Chicken Recipe Wet Dog FoodCesarCesar Puppy Filets in Gravy Puppy Food, Chicken Recipe Wet Dog FoodWet // No. 24 on the labelNulo Culinary Harvest Turkey & Herring Recipe Dry Dog FoodNuloNulo Culinary Harvest Turkey & Herring Recipe Dry Dog FoodDry // No. 24 on the labelI and Love and You Naked Essentials Grain-Free with Lamb + Bison Dry Dog FoodI and Love and YouI and Love and You Naked Essentials Grain-Free with Lamb + Bison Dry Dog FoodDry // No. 24 on the labelPure Balance Pro+ Sensitive Skin & Stomach, Salmon & Rice Recipe Dry Dog FoodPure BalancePure Balance Pro+ Sensitive Skin & Stomach, Salmon & Rice Recipe Dry Dog FoodDry // No. 25 on the labelNulo Culinary Harvest Beef, Pork & Lamb Recipe Dry Dog FoodNuloNulo Culinary Harvest Beef, Pork & Lamb Recipe Dry Dog FoodDry // No. 25 on the labelNulo Culinary Harvest Small Breed Beef, Pork & Lamb Recipe Dry Dog FoodNuloNulo Culinary Harvest Small Breed Beef, Pork & Lamb Recipe Dry Dog FoodDry // No. 25 on the labelAbound All Life Stages Superfood Blend Salmon, Egg & Pumpkin Dry Dog FoodAboundAbound All Life Stages Superfood Blend Salmon, Egg & Pumpkin Dry Dog FoodDry // No. 26 on the labelAbound Adult Lamb & Brown Rice with Avocado Dry Dog FoodAboundAbound Adult Lamb & Brown Rice with Avocado Dry Dog FoodDry // No. 27 on the labelAbound All Life Stages Chicken & Brown Rice Dry Dog FoodAboundAbound All Life Stages Chicken & Brown Rice Dry Dog FoodDry // No. 28 on the labelAbound Grain Free All Life Stages Salmon & Sweet Potato Dry Dog FoodAboundAbound Grain Free All Life Stages Salmon & Sweet Potato Dry Dog FoodDry // No. 28 on the labelNulo FreeStyle Turkey & Sweet Potato Recipe Grain-Free Dry Dog FoodNuloNulo FreeStyle Turkey & Sweet Potato Recipe Grain-Free Dry Dog FoodDry // No. 28 on the labelNulo FreeStyle Lamb & Chickpeas Recipe Grain-Free Dry Dog FoodNuloNulo FreeStyle Lamb & Chickpeas Recipe Grain-Free Dry Dog FoodDry // No. 28 on the label

Sources

What we read

Checked October 1, 2026.

  1. 1 Absorption of monoferric phytate by dogs The Journal of Nutrition, 1979 // Journal
  2. 2 Diets containing naturally occurring iron or naturally occurring iron plus supplemental ferrous sulfate both maintain normal hematological status in adult dogs Journal of Food Nutrition and Metabolism, 2019 // Journal
  3. 3 Ferrous sulfate monohydrate INRAE-CIRAD-AFZ Feed Tables, n.d. // Database
  4. 4 AAFCO Dog Food Nutrient Profiles AAFCO, 2013 // Regulator
  5. 5 Water Treatment Chemical Supply Chain Profile: Ferrous Sulfate U.S. Environmental Protection Agency, 2022 // Government
  6. 6 Ferrous Sulfate American Water Works Association, 2006 // Industry
  7. 7 Reading Labels AAFCO, n.d. // Regulator
  8. 8 Iron Pet Poison Helpline, n.d. // Industry
  9. 9 Comparison of Absorption Characteristics of Iron Glycine Chelate and Ferrous Sulfate in Caco-2 Cells International Journal of Agriculture & Biology, 2013 // Journal
An ingredient on its own tells you very little. What matters is how much of it there is and where it sits in the list. That is why we weigh the top five rather than reacting to any single name further down. Back to the wiki

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