How old is she? Arthritis can be in the jaw as well, which can reduce hay eating, or the antibiotics could be reducing her appetite. With my senior it helped to offer him oat hay in little piles near where he rested, but eventually even that wasn’t quite enough. If her hay consumption is really down then you may need to start supplemental feeding with a recovery food. My bun really did well with Emeraid Herbivore Sustain. The Emeraid (or other brand) would definitely help support her gut while she’s on the antibiotics.
It can also take some time to get the pain meds dialed in. If arthritis is severe, a second med can be added, such as Tramadol. My senior bun was on a combo of meloxiam and tramadol in his final year and it really helped him.
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The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.