I give Bovi-gold 5 L5 to all cows about a week after they calf. It won't hurt the nursing calf. All heifer calves after 6 mths get the same thing followed with a booster 4 weeks later. All others Bovi-shield. I've never lost one to any sickness by following this program. Also, at birth, or at least as close to birth as possible, I give calves 20 cc of polyshield.