Help my chickens poop is bright yellow

[KemzWade19]

my chickens free range and one day I saw that my rooster was acting weird and next thing you know he is going lame and his poop is bright yellow and it’s runny and he’s not eating just drinking. What is harkening and what should I do?! Picture below

 

[Jener8or]

It could be vent gleet. I'm not sure if it would cause him to go lame, but definitely could make him lethargic. Here is a good article by Lisa Steele (Fresh Eggs Daily) on vent gleet:
https://www.fresheggsdaily.blog/2013/09/vent-gleet-symptoms-causes-and-natural.html