Grass Tetany

We just had one of the registered Angus cows go down this morning after receiving 3 inches of precip in the past week and the first warm weather of the spring to get grass growing.  I knew it was coming, just had to figure out who would be first.  This cow calved the 1st of April and is a fairly heavy milker.  We have had the high magnesium mineral out since the first of March and have had some grass hay set out in self feeders for the past month.  We caught her pretty early and got an IV in her and she was able to stand and quit shaking.  Not out of the woods yet, but one of the more positive looking ones at this point.  Kept her in and will probably just put her on hay for a week or so.

We run in common with other family members who run Gelbvieh and Simmy cross cows.  Ours are Angus and Angus x Limousin.  The Gelbvieh and Simmy cows seem to never go down with grass tetany while the Angus and Angus x Limmie crosses are the only ones affected.  Anyone have any theories why the difference between breeds on this?

Glad to hear she is up!  Hopefully she'l have a full recovery. 

We've had 2 go down this year.  One was one of our heaviest milking young cows.  The other was an old hereford.  They had access to the hi- mag mineral for some time before going to grass and have had it free choice since then too.    My theory is that for some reason these individual cows did not consume enough or they had a higher requirement.   

I use the Crystalyx tubs Hi-mag product. They overeat it and it is expensive but consumption is plenty on it. I think its actually like a 10% protein also.

She is up and acting normal again.  First one we ever saved.  Usually find them too far gone staggering around and then when you try to handle them, they fall over and the convulsions start.  This cow did have a couple of minutes of convulsions when we put a rope on her, but she quit once the IV started.  I put her in the corral and she is going to get hay for a few days.  Checking the others every few hours because tomorrow is going to be in the 70s and the cool season grasses are going to be growing really fast for the next few days.  That is the prime conditions around here for grass tetany. 

My vet's theory is that the Angus and Angus cross cows just run a higher metabolism than the Gelbvieh and Simmental cattle, which makes them more susceptible to getting their metabolic processes out of whack, leading to grass tetany.  Sounds as good as any explanation.