Muskrat(not Mudcat)Love was written by none other than 24 yr old Texas singer-songwriter Willis Alan Ramsay, an unlikely person to have done such a song since his one and only album featured stuff like 'The Ballad of Spider John'.
I loved the band America when they first came out with those songs. I was 15 and just learning to play the guitar and felt sure those lyrics were very deep, just as I felt Neil Young was very deep. All my peers knew all the words and it was great material to get attention with if I took my guitar to any of those awkward adolescent parties.
I played the verses for 'Horse' with an Eminor and then a variation of a B7 (2nd fret)with the D and the high E strings open and the bass E at fret 2. The chorus went from a Cmaj7 at the 7th fret (E-7,B-8,G-9,D-10) to Gmaj7(same fingering slid down to the 2nd fret). One of those songs that looked and sounded much harder than it was and therefore to a fledgling strummer it was gold.
I work in the field of addictions now and looking quickly through the lyrics I can see a possible drug metaphor. That may be giving the lyricist more than his Dewey. I do remember heroin was sometimes referred to as horse.