Your guess that your buckles are horse related is correct. Your buckles are from a version of wagon-pulling horse harness. This buckle form is used where four leather straps join a rectangular or square buckle at the compass points (the North side, East, South, & West). One of those four straps is usually the Trace strap... so this buckle is called a "3-loop Trace buckle."
I do not have a photo or diagram showing your exact buckle. But I've definitely seen it in late-1800s/early-1900s "Saddlery" Horse Harness equipment mail-order catalogs... such as the E.M. Eilers & Co. 1907 catalog. I'll attach a catalog drawing showing a very similar version, listed as a "Trace buckle."
I realize the catalog diagram I've posted below has only 2 peripheral loops instead of the 3 loops seen on yours... but it shows you the basic form. Here's a Link to 2 pages in the online copy of the Eilers & Co. 1907 catalog.
Date taken from Price changes applying to Catalogue no. 2 pamphlet inserted into front cover
archive.org
Have fun page-turning through the catalog to find your exact buckle. BTW, it will be well worth your time to do that, because you will very probably see several other buckles you've long wanted to know the historically-correct ID for.
Also, see the "full" horse-harness drawing below, and look along the Trace strap for 4 straps joining at a buckle.
