Liver lesion

Is there any extra fat in the abdominal cavity and spleen enlargement?

It seems a lesion by Clostridios

The liver looks just like the livers we see in turkeys that have Histomoniasis or blackhead caused by Histomonas meleagridis. The "target " liver lesions representing areas of necrosis are classic. Now, chickens can be infected with histomonas but they do not show clinical signs or have post-mortem lesions, but there is always a first. I would suggest sending in bacterial aerobic and anaerobic cultures just because it could be bacterial too. Then before you do any PCR which can be more expensive, do histology on the liver first. If it is Histomoniasis and you have Histostat in your country, you can treat them. Histology can also reveal the presence of tumors etc. In the US, arsenicals such as Histostat that were used for blackhead have been banned. If these birds are on the floor or out on range, you may want to control the cecal nematode Heterakis gallinarum which carries the eggs of H. meleagridis. Good luck!