
Hi Helen,
Yes, I agree it is confusing ... very. My advice is only relevant is you are supplementing a complete food with a significant amount of meat.
I feed my dogs a mix of complete food and home-cooked food. The home cooked food is whatever the people in the house had for their evening meal or an alternative; always and mostly a protein of some kind (red meat, chicken, fish and occassionally egg) along with a bit of vegetable and potato or rice.
For example, (you can find very detailed nutrional data on a site www.nutriondata.com) one cup of baked, skinless chicken breast has 21 mg of calcium and 319.0 mg. That is way off the ratio of 1:1 to 2:1 calcium:phosphorous ration which is required for dogs - so you can see that if you fed large amounts of chicken you would need to add more calcium to balance the relatively larger amounts of phosphorous.
I did a lot of research on this a while back and below is a quote from some site, which I do not recall, but it sums up the advice:
"Adult dogs need around 800 to 1,000 mg of calcium per pound of food fed. They also require the calcium to be supplied in a proper proportion to phosphorus.The ideal calcium:phosphorus ratio in the canine diet is between 1:1 and 2:1. Meat contains a lot of phosphorus, so the more meat a diet contains, the more calcium will be required to reach the correct calcium:phosphorus ratio. Adding 800 to 1,000 mg of calcium will provide the correct calcium:phosphorus ratio even for a high-meat diet, unless you use a calcium supplement that also contains phosphorus. In that case, moderately higher amounts of calcium may be needed to balance out the additional phosphorus contained in the supplement."
So - to make sure the home cooked food I give my dogs is nutrionally balanced I give the a doggie vitamin (which is probably not necessary) and a few times a week I give them some extra calcium. I just buy chewable tablets from Holland and Barrett - but any kind will do - you look for calcium-only tablets of calcium carbonate, chelated calcium, calcium gluconate or calcium lactate. If your family eat a lot of eggs you can also dry the shells and grind them to a powder, one whole eggshell is about 1,800 milligrams of calcium carbonate.
If the Beaphar supplement is on the low side for phosphorous it's better than nothing for dogs fed a mostly meat-based diet. However, I don't know what they mean by a "mostly meat based diet". I assume they do not mean dogs fed raw meaty bones, but your guess is as good as mine.