Striations / striping of goose feathers

[TheCrazyBirdGuy]

I feel like sometime a while back I read somewhere on this forum about striations on bird feathers possibly being health indicators. A goose i care for, Flip-Flop, (mix Embden and Chinese) started getting these on a few of his feathers. It could just be damage from interacting with the other male geese... but I just thought I would post it up here to see if anyone had any info. I’ve searched Google and this site but pretty much all I come up with on google is pillow related issues and i didn't see anything on here… I've attached pictures. Thanks.