I buy a huge bag of seaweed powder/granules from Ascotts Smallholding. It is quite expensive, but lasts forever. I alsoadd a bit into the concentrate for the sheep. I am sure you can get smaller packs for horses, but it would work out more expensive in the long run. As long as you keep the seaweed dry, I don't think it will go off.
Once my female is coming up to six weeks prior to kidding, I start to feed three times a day, just to balance the increase out.
The BT type girl was on the following:
6 weeks to kidding - 1pound conc + sugarbeet (1 scoop, not measured)
5 weeks to kidding - the same but three meals
4 weeks to kidding - 600 g conc + shreds
3 weeks to kidding - 750 g conc
2 weeks to kidding - 1 kg conc
1 weeks to kidding - 1.2 - 1.5 kgs, but she wouldn't finish it all.
Lots of veg, anything they like at this stage, so they keep eating. the problem is that the developing kid(s) will take up a lot of space, stomach a lot smaller and the goat cannot eat large amounts in a single meal anymore - lots of food in smaller portions and often. the other danger is pregnancy toxaemia, which is when the nutrients required by the kid(s) are higher than the goat can take in in feed and these are therefore taken from her tissues (ketosis results) - sweet, acetone smelling breath and possibly also urine, goat becomes lethargic and very quickly deteriorates. If that occurs (it is quite rare, and with stepped up feeding and observing the goat during feeding it is also quickly noticed) a quick drench with glucose (I have a bottle from the vet ready - will check the tradename tomorrow - its too late now) before the vet is called can help enormously. Both of mine were totally fine last year - but I was worried for weeks before the kidding, and yes I had a set of scales in the goatshed to measure out their feed. I made a plan up for the last six weeks, and inctreased by about 20 to 30 gs per day over the two meals. In the end I left the sugarbeet shreds out, as it was quite warm by then and I thought the mix was higher protein, so better to eat that.
But I guess quite a few weeks until you get to that stage - and by then we will all be getting near to kidding.... I can't wait! First one due beg of March!