Most cattle diets aim for a calcium to phosphorus (Ca:P) ratio of about 1.5:1 to 2:1. Cattle can tolerate a wider range if phosphorus is adequate, but a ratio below 1:1, meaning more phosphorus than calcium, can cause problems. Your nutritionist or vet can set exact targets for your herd.
Why the ratio matters
Calcium and phosphorus build bones and teeth, and are also needed for milk production, muscle function and energy use. Too little of either reduces growth, fertility and milk. Too much phosphorus relative to calcium can interfere with calcium absorption and, in grain-fed steers and bulls, contributes to urinary stones (urinary calculi).
Typical targets
- Growing and finishing cattle: about 1.5:1 to 2:1. Grain-heavy diets are low in calcium, so limestone is commonly added.
- Beef cows on pasture: forage supplies most of the calcium. Phosphorus may be short on mature or weathered forage, so a mineral may be needed.
- Dry and fresh dairy cows: calcium management around calving is closely managed to prevent milk fever. Do not guess. Work with a dairy nutritionist.
Common sources
- Calcium: alfalfa and legume hays, limestone and other calcium supplements.
- Phosphorus: grains, brans, distillers grains and phosphorus mineral supplements.
- Complete mineral mixes: free-choice minerals formulated for your region and class of cattle. See cattle mineral blocks and how to make a mineral feeder.
How to get it right
- Test your hay and forage for calcium and phosphorus.
- Add up all sources: forage, grain, minerals and by-product feeds.
- Choose a mineral supplement that fixes the gap, instead of adding both minerals blindly.
- Check intake. Cattle that eat too little mineral may not get enough, and too much wastes money.
Other trace minerals matter too, but some, such as selenium and copper, are toxic if overdosed and vary by region and species. Use products made for cattle and follow the label. Sheep and goat minerals can be dangerous to cattle if they contain too much copper, or vice versa.
For pregnant animals, see choosing a supplement for pregnant cows and the pregnant cow feeding chart. This is general information, not veterinary advice.
Bottom Line
Aim for roughly 1.5:1 to 2:1 calcium to phosphorus, test your feed and use a mineral made for your cattle. For dairy cows near calving, get a nutritionist’s help.
