Post Gastropexy surgery questions

Hi vets My 14 years old chihuahua had a gastropexy last Tuesday afternoon. I have heard GDV is quite rare in small breeds but still can happen. Anyway, Monday midnight his stomach did get full of gas and he was trying to vomit but nothing was coming out except for a little bit of a transparent liquid. The vets recommended the surgery, everything went well, he is now recovering home. Mi questions are: He is currently eating Hills a/d but he is very gassy. Is that normal? Is that the right food? What are other food options for after he is fully recovered? I have a follow up appointment this coming Wednesday but I wanted another opinion from other experts if you don’t mind. I would really appreciate it. I have attached some pictures of how the xrays came up that night. TIA