Seems the horse data or the rendering of the data is missing.

Not sure when this initially occurred. But versions currently used.
Relates to: DarkPacks/SevTech-Ages#2320

Forge: 14.23.4.2705
Mod: 2.5.256

For some reason the changes to the language file didn't get pushed. Should be fixed in the next release which will be on curse as soon as they approve it.