This is about as stupid a thing as I have ever heard. Two thirds of Texas is Fever tick territory. They don't come from Mexico, they are native to Texas as well. I grew up on a Texas Cattle ranch and ticks are just a part of raising cattle. There is nothing you can really do about it, there is no general treatment to get rid of the ticks, no real preventative measures you can take. If you think you have a cow with the fever you just have to quarantine and treat.
Finally, if they are bitching about Mexican cattle coming onto their property, fucking tend to your herds and fences. I spend half my childhood fixing fences. The days of free range cattle are fucking long over in Texas. You must have a fence, you have to actively herd, or you will lose your cattle.