Ropo, have you contacted the State's Attorney General? It sounds like there is alot of corruption in the local police agency and the SAG is suppose to investigate such matters. If the sheriff's dept. did contact the uncle the night before to warn him that is obstruction of justice and under the color of authority.
The other posters are correct about the warrent, if they truly need one, a judge is available to sign one 24 hours a day 7 days a week. But the paperwork has to be submitted by law enforcement.
You've hung on this long, don't give up, hopefully the judge will be so p'oed she'll chew the sheriffs dept a new one and order your horse returned that day.
I wish all us posters lived close by, I would be happy to saddle up with a .30-.30 and my .45 and go get your Max back for you...and they wonder why some people take the law into their own hands.