Thanks and I will leave it there.
The problem was the acidity ratio in the feed. As they were eating more, their little stomachs reacted to the increase amount of chemicals which were in the total mix ration..Ican't remember the exact name of the toxin, but I can look it up later, so it was a form of 'food poisining'.
However, the more sturdier calves did not hvae the same reaction as after the three calves died , we just started to feed grass. The vet said this was a good thing and probably changed the others lives.
It was a frightening experience as i said these calves just literally rolled up and died.
thanks for every ones concern.