Eleanor Kellon, VMD
These are all nutrients involved in the maintenance and formation of bone, but like all nutrient supplements they will only have an effect if the horse is deficient and they correct the deficiency. At the higher dose and average calcium concentration it only supplies 2 grams of calcium compared to 12 g in a serving of U Balance Foundation and the 20 maintenance requirement of an adult 500 kg horse. The vitamin K1 is 5.5 mg/serving vs 40 mg in UBF; point being you can do a lot better with a high quality vitamin and mineral supplement.
More to the point, vitamin D and K deficiencies have never been found in a horse. The claim on the web site that cutting and drying hay destroys vitamin K is false. For example, dried herbs have more vitamin K than in their fresh state https://www.sciencedirect.com/science/article/abs/pii/S0889157515000381 .