These are all very good answers. I shoot for an April 3rd calving start date, which to me means that I need to have the cows and heifers located in their respective calving pastures no later than March 20th. That gives me a two week leeway period, and I will always have cows and especially heifers calve before the official starting date. The heifers tend to be earlier than the cows. I don't know if that is because of their age, or that sometimes "heifer bulls" tend to genetically have a little bit shorter gestation time. As an added note to the March 20th prepare date, I made a list, several years ago, of important things to make sure you have, such as eartags, medicines, etc. and you don't want to be wondering where chains, straps or a calf puller five minutes for you need. it.