I remember the injectables for horses. Strangely, it didn’t bother cattle. They still inject cattle with it. We use the paste on our horses (and ourselves now).
Ivermectin injections were Intramuscular for horses, gave sterile abscesses, and septic abscesses. Cattle is subcutaneous. Or pour on.
Horses are just so darn finicky, they're subject to so many little ailments that can turn fatal in the blink of an eye. I feel very blessed that my long-time ride, a TB racing-bred mare, was healthy and sound for almost her entire life. She developed a niggling little lameness that we could never pinpoint when she was about 27 or 28, and we loaned her out to the Special Olympics. For a TB she was just about the sweetest girl you can imagine, she loved those little kids. There would be two of them feeding her peppermints, two painting her hooves, and 2-3 of them brushing her and she would just stand there and glow with happiness. She would hang her head over the farrier's shoulder and nibble on his hair while he was shoeing her. But she hated new shoes, and she expected me to sit down in her stall while she laid her head in my lap and stuck all four feet out straight while she got used to them.
She just lay down in the pasture one night when she was 30 years old and didn't get up again.
Rest in peace, sweet Gracie!