The usual lambing and prelambing one is the blue top, no 6, 20% calcium with magnesium, for sheep. I'm told it's the same as no 5 (red top, 40% for cattle) except half as strong. However, when I check the data sheet, I find that the magnesium is the same in each, it's only the calcium and the boric acid which is double in the red top, plus the blue top also contains glucose while the red top does not. So it's not exactly the same thing to give a sheep half of the 40%.
No 2 is the green top, for straight hypocalcaemia in cattle. No magnesium.
So for the OP, ideally you'd get 20% No 6 (blue top) but if pushed you could use 40% No 5 (red top) at half the dose rate.