Hi , I'm James DVM MRCVS and would like to help you with your question
Sorry to hear about Mylo
Do you know if he is painful anywhere ?
Is he lame ?
Is there anything else you may see besides his lack of energy ?
There could be many things which could lead to Mylo not wanting to eat .
1. digestive problem - ate something he shouldn't have and no has an upset tummy (the diarrhea is still to come)
2. Some other infection involving other body organ , liver , kidney
3. Some disease of non infectious origin , lets say some disease he was born with and now is causing him to be lethargic
4. Some trauma or bruising .
All these ends need to be investigated but most importantly is to keep Mylo hydrated as you wisely monitored .
if Mylo is not drinking at all then a visit to your vets (or out of hour vets) is necessary to have him checked out.
A basic blood test will let you vet know if Mylo is dehydrated and in need of fluid therapy, an Xray of the abdomen and perhaps an ultrasound scan will give us much information in regards to anything in the stomach , intestines even the live , kidney and pancreas which might be inflamed and needs treatment .
The point being that if Mylo does not improve , he must be seen and better sooner then later.
This will allow us to diagnose Mylo and and treat him as needed .
I hope hope this helps.
Please let me know if you wish to ask anything more and I would be happy to help.
All the best.
thank you ,out that Mylo was pining for my daughter who was away at my sisters, as soon as she returned Mylo returned back to normal