Hello, and welcome!
I'm so sorry Mowgli is experiencing these problems.
Is the discharge from his anus or his penis?
Since he's had a bad time with a UTI in the past, if you see a whitish/yellow discharge from his penis, he could have another UTI or even a urethral blockage, which is a medical emergency in male cats. If you can't keep track of his elimination because he basically goes outside, this is a problem. I assume he used the litterbox enough, inside the house, for you to see the discharge. Here is more information on urinary problems in cats:
If the discharge is from his anus, he could have an intestinal infection, intestinal parasites or an anal glad problem. The fluid inside the anal glands (located on either side of the anus, under the skin) may be impacted or infected. The fluid may need to be expressed (emptied) by the vet. Here is more detailed information:
It's very possible that he may have either ingested or tangled with another 'critter' outside, and this is causing his problem. He may have been bitten or stung by a venomous insect, snake or spider, or, as you suspect, he could have eaten all or part of one of his 'catches.'
Blue Buffalo is a good food, and I'm not surprised that you said he prefers the cheap supermarket food.......most cats, do! lol That's because they fill it with artificial and inferior ingredients that taste good, but are not good for them.
At this time, from your description of the situation, it's important that Mowgli is evaluated in person by a vet, as soon as possible, so you can get a definite diagnosis and treatment.
I hope all will be well with your furry boy; he sounds like a darling!
Please let me know how he's doing and what the vet tells you. Thanks!
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