A cow does lactate for around 10 months before it would need to have a calf again. Also, a cow produces faaar more milk then one calf needs. Source: live on a

A cow does lactate for around 10 months before it would need to have a calf again. Also, a cow produces faaar more milk then one calf needs. Source: live on a dairy, grew up feeding calves. Used milk replacer for a while but then switched to plain milk cause it's healthier for the calves (no surprise)