Caity, I suppose its a fairly common problem in some areas. I wouldn't think it would be much of a problem in the middle of July, however. Guess it depends on the conditions where you're located, which nobody knows but you. Knowing at least which hemisphere you are in would be helpful.
Grass tetany is caused by an imbalance of calcium and magnesium. Imbalalnce isn't really the right term but it's the besT I can come up with off the top of my head. Typically it's seen in rapidly growing spring grass and just fresh cows. From the few instances I've seen of it, rapid treatment by administering magnesium and calcium have fixed the problem. Unfortuneatly, most of the cases I've seen have been dead cows because it wasn't caught in time.
Here's the deal! If you provide more information as to the area, forage, symptoms and other observations, someone on this board may be able to provide better information, advice.
Are they on irrigated pasture, or are you getting alot of rainfall? Grass tetany or grass stagers is usually only seen when the grass is growing so fast it doesn't contain enough magnesium. The quickest & safest way to fix the problem is give them an enema of epsom salts (magnesium sulfate). If their body needs it it will absorb the magnesium through the mucus membranes of the rectum and they will just walk away as if nothing happened. If not it just comes back out. To keep it from happening put out a Hi-Mag mineral mix.