[Jazzy's mom]

Last Wednesday I dewormed my 30yo gelding with Zimectrin Gold. I have never had an issue with using any dewormer before, nor with using zimectrin gold. He got the wormer around 1:30pm. I received a call from the BO at 10 saying that my gelding was down and wouldn't get up. I made a 45min drive in about 30 and by the time I got there he was up but not himself. Temp was 99, resp normal. No kicking at belly or acting colicy but he did keep cocking his left leg. No appetite, he didn't want his dinner and showed no interest in any of the buckets of grain in the aisle for morning feeding. When he didn't know I was watching, he acted absolutely exhausted, head down and eyes droopy. He eventually went back out and went back down, no thrashing but he was mostly flat out on his side. I spent many hours in 40 degree weather curled up under a horseblanket on a stack of hay sure that my boy would be dead each time I checked on him. I finally went home around 2am as there just was nothing I could do. I chose to not call the vet as he was not acting painful. I honestly thought he would be dead by morning.
The BO called me in the morning to tell me that he was up and acting normal and hungry. He has been acting normal since then.
Could this have been some sort of toxicity reaction to the wormer? I just got the feeling that maybe his liver isn't working like a younger horse and maybe the chemicals overwhelmed him? Any thoughts would be appreciated. At his age should I just not deworm him again?

[littlecreek]

My guess would be that he had a larger than normal worm die off, which can make them feel icky. Glad he's back to normal. What does your vet say about all of it? I've used that product a number of times over the years with no problems.

[D Taylor]

Personally I do not use ZG. Too many bad reactions to it. Why go there with other choices out there?

Search the threads here and other forums and I know you will find plenty to read about logging others bad experiences with it.

[JB]

Yes, there is no reason to use ZG - even Merial admits now it can cause ulcer issues. Equimax works just as well and simply does not have that issue.

Your deworming program needs to switch to a FEC-based program. You did use chemicals that are appropriate for this time of year, even if a FEC had showed clean. But his age is no reason not to deworm him again. He doesn't have a built up immunity to strongyles just because he's 30 - it's not like a virus

I would do a FEC on him in 12 weeks and just see what's what. If he's clean, do another FEC 4-8 weeks after this, which will put you into the March/April time frame. At that point, you'll use either Equimax or Quest Plus, depending on his weight (I would NOT use QP if he's remotely underweight, no matter how healthy he is otherwise). Even if the FEC is clean you'll need to take care of bots and tapeworms.

As to your original question - yes, some horses just don't handle certain chemicals well, even the milder ones like fenbendazole. But, that's just not common.

[Jazzy's mom]

Thank you JB.
He has been dewormed regularly so I don't think it was a case of worm die off.
I will speak to my vet about going to a FEC based program. My biggest concern is that if he does have reduced liver function that any de-wormer might trigger a similar reaction. I will probably stay away from QP. He is not underweight but he is very hard to keep weight on due to a lackluster appetite.

[D Taylor]

If you think he has compromised liver function I suggest you research milk thistle extract.