I agree with what Texan said, and you could also try to keep in mind that where ever that grass is growing back - just like around the manure - it's a good thing! If it's growing back, you are accomplishing something. I would strongly suggest you not mow that grass, and to be honest I can't understand why you would. Be patient, give Mother Nature time, and as the manure breaks down, the nitrogen levels will drop in those spots where the dung has been. As the soil improves over time, you will have lush pasture, with a wide diversity of species, and as long as you don't graze it down like carpet, or mow it continuously, you'll be doing fine.