Before the invention of the current adavantage and frontline, my friends had a dog who was allergic to flea bites, they tried everything, including garlic and yeast tabs and found them completely ineffective, dont want to be a wet rag on your findings, everyone is different and experinces things differently, just a "Heads up". You might also research vitamin overdose issues, since you are giving your larger dog such high doses - vitamin over dose especially over long periods of time can be harmful to you (if you take them) and your pet.

I know there are some here who will not agree with me, however.

I have four large dogs. In my 18 years of having them, I have never had a flea problem. This goes for city and country living. I attribute it to two things.

First, their diet. Two of them are on hypo allergic food, the other is on a very high quality one with no fillers etc. I've read lots that diet makes a huge difference when dealing with fleas.

Second. I keep them clean. During the warm months, they get a bath about every 4 weeks, either by me or the groomer, depending on how dirty they get. I vacuum at least twice a week, and keep their bedding etc. clean by washing it at least once a week.

My theory is not going to work for everyone. I use it because of horrible lower G.I. my dogs have experienced I've encountered with pills, collars and ointment.

If your dog has an allergic reaction to fleas, other things will probably have to be done. But I do think what I'm doing helps lots as far as being preventive.

SG

Luckily they are young and healthy with no known allergies. Hopefully I can keep them that way. I have done some research on the vitamin requirement for them and the Flea - D does not seem to contain over the daily required amounts for their ages and weights.Here is a list of the ingredients-
Supplement Facts
Serving Size N/A
Servings Per Container 180 Wafers

Amount Per Serving: % Daily Value

Potassium 50 Mg: N/A*
Phosphorus 45 Mg: N/A*
Calcium 15 Mg: N/A*
Vitamin C 15 Mg: N/A*
Sodium 3 Mg: N/A*
Vitamin B-3 2 Mg: N/A*
Vitamin B-2 2 Mg: N/A*
Vitamin B-1 2 Mg: N/A*
Iron 1 Mg: N/A*

* Daily value not established

Other Ingredients:
Brewers yeast, primary grown yeast, garlic powder, vegetable oil, and natural chicken flavoring.

Does Not Contain:
Sugar, artificial flavorings, color, or preservatives.

Yeast may not be a chemical however, Yeast in itself is not a natural food ingredient for dogs at all, it's a fungus which can add gas, change the calcium phosphorus levels as yeast has a high phosphorus content, it also changes urinary and digestive systems which can lead to an overgrowth of yeast in the system. What it does have is certain minerals and Vitamin B complex which could be obtained with more species appropriate foods such as fish, bones, meat, veggies, etc.

Brewers yeast and garlic are NOT safe for dogs or cats. Garlic causes anemia. Both are on the SPCA's toxic food list for pets.

People just love to argue with this however, saying that a little is okay or that their dog has always done fine with those foods, but knowing what veterinarian's findings are on these foods, I would never take the chance and give them to my dog. I hope you feel the same way.

Here is a link that might be useful: Garlic

I made a mistake, brewer's yeast is not on the SPCA's site but it does cause bloat which can lead to death.