If it's not itchy then it's not scab nor mites or lice. When you catch hold of him, you should be able to tell if there is only wool loss or also any infection. Don't use an antibiotic spray unless it's infected.
Almost certainly it's caused by friction against the bars of the hay heck, and won't cause him any problems at all. If you think it is sore you could use Sudocrem to soothe, or if you think there is a possibility of his getting an infection, Septiclense antiseptic spray to both soothe and clean.