I assume that by posting here, in the manner you did, implies that you are not going to have a vet sew it up. So you can either sew it up yourself, or let it heal. Regardless of which, consider giving a dose of broad spectrum long acting antibiotic and Tetanus vaccination. If you're going to sew it up, get the calf in a squeeze chute where he can be stabilized so neither one of you get hurt. Flush the cut out with a copious amount of water, apply some antibiotic ointment and reapproximate the cut edges with suture. Dress with more antibiotic ointment. If you are not planning to sew it up, flush it out and dress it with antibiotic ointment or you might consider a product called CutHeal. It should be checked and dressed daily until it is nearly sealed. A third option is to flush the cut out and dress it with antibiotic ointment and kick the calf out and quit worrying about it - for the most part cattle heal well. All bleeding stops - eventually.