I have had a ongoing problem with mostly roosters in that they seem to get a adult version of pasty butt. Their poop hardens and clogs their vents. I had two little D’uccle roosters die last year. And I currently have 3 more roosters that I have to constantly monitor and bathe to remove the poop Their vents also get very red and swollen. They are on Purina Flockraiser which has prebiotic’s and probiotics. They get to free range every day. What on earth could be going on?