Role of genetics is a possibility. if there lineage is prone to be pot bellied then it is as is.
another possibility is nutritional, usually we need to satisfy the nutritional need and also the volume intake of the animal.
In the nutritional side if the feeds does not have the necessary nutrition the animal needs, it will eat more than the usual capacity of their stomach. So tendency the stomach will increase it size na to the point na overstretch na sila.
Like you said you are mixing d1 and concentrates, so i would suggest to ask your supplier if he/she could provide you a simple formulation in every stage ng baboy nyo.
