Glad I'm not the only one who's clueless on this. As they say someone must have had a need and put it to use, maybe ask who you bought the dozer from what he used it for and let us know.
As I said previously the guy I bought it from didn't know either. He said it was owned by one previous owner before his dad bought it.
Presumably the original owner probably had this welded on. It is just a heavy wall pipe, capped at both ends. I am amazed nobody else seems to know for sure what it was meant for, thought I was the only one who didn't recognize what it's purpose was.
I'll leave the pipe on there, at least until I re-skin the blade, it does no harm.
Speaking of re-skinning the blade, I had to patch the blade already. There was a 3" strip of mud above the cutting edge that never got scraped off or washed off. When I washed the dozer with a pressure washer I found out why. There was no metal here above the cutting edge from one side to the other and the inside of the blade was full of hard clay. I pressure washed some of it out and got covered in mud, but most of it I had to chip it out with an air chisel. Welded in a patch from one side of the blade to the other. Turned the cutting edge over at the same time, what a fun job burning off the worn down cutting edge bolts with an O/A torch, you get better at it after the first couple of bolts.
At least the bolts and nuts were fairly cheap at JD.
Now all I need to do is weld on new grouser bars for the pads, fabricate some brush sweeps for the canopy, replace pins and bushings on the 6 way blade and paint it all. Thankfully the U/C, motor and trans is in good shape.