Thanks Nic, you have confirmed my thoughts.
I couldn’t find a medical reason for this so my first thought was the hog(s) might have stumbled upon some bread left out for the birds by a neighbour.
However, after an attack on our fatballs by magpies and starlings the ground is covered by debris. In fact I first noticed the hogs had returned after a number of years when I saw one foraging below the fatballs, crunching the sunflower seeds and no doubt hoovering up the suet scraps.
The poo was “normal” in other respects so I don’t think this is a problem, unlike the green poo I see occasionally.