Just back from the vets. X ray is clear except for a small amount of what might be residual faeces or possibly inflammation from the constipation.
Either way we think the fish oil (plus more bathing and massage) did the trick.
I'm going to try giving him 2 more chicken hearts with fish oil capsules today to try and make the next defecation easy, and if he keeps taking hearts, graduate to hearts packed with Herp-a-Vite for a while to get some vitamins and minerals into him while sticking to soft food for a while. before trying a whole animal.
Happy day!
