Is yellow sulfur blocks good for bred cattle?

No. Cows can easily get sulfur toxicity if fed pure sulfur in a block form. It's best to feed sulfur as a supplement form mixed with other minerals, and in small amounts. The maximum amount cattle should get per ration DM is 0.4%. The optimum amount that cattle need is 0.15% per ration DM. Any level above 0.4% per ration DM is considered toxic for cattle.

Consider supplementing cattle with feeds that are high in protein. With that, most feedstuffs contain sufficient sulfur to meet their needs.

Note though, that copper requirements are increased by both sulfur and molybdenum. Selenium can be used to replace sulfur in some organic compounds. This only applies to areas that are selenium deficient, though.