I started calving right at the 1st of January and finished up the end of February. I have not noticed any of my cows coming in standing heat. Ive got a bull with them. Ive seen the bull follow a couple but never saw him ride any. Ive not noticed any cows get bullish either. These are 4-6 yr old cows. Of course im out there for 15-20 minutes a day and they are out there 24 hrs a day!