Nathan is quite right, and this is a perfect example of why "you" or I should not give needles to horses owned by other people!
I look on giving vaccines as a routine procedure & have been vaccinating my own horses for over 30 years. 30 years ago it was common place for horse owners that were good at giving needles to help out friends or neighbors who were not so good at giving needles by going over & vaccinating their horses for them. I won't do that any more. Here 30 years ago we didn't hear people talk of lawsuits. Now is a different story! In our litigation happy world it would be financial suicide to give a vaccine to someone else's horse & have the needle break off or the horse get a serious reaction!
I've had needles bend but never break when vaccinating horses. I have thought, though, about the needle breaking and hoped that it never happens to me. It does happen often enough when vaccinating cattle. (I even know of someone that bought a cut of beef from the store & found a piece of needle in it! It was determined that the needle wasn't placed there maliciously--it was a vaccination needle that broke off & got left in the animal. Seems to me that they said that needle had migrated, because the cut of meat it was in wasn't from a vaccination area on the animal. But anyway, I don't think that they're making needles "cheap" or defective now, it's just one of those things that can happen and once in awhile does happen.