One Stop shop for all Resources you need!
https://extension.psu.edu/heat-detection-and-timing-of-insemination-for-cattle
https://www.fda.gov/animal-veterinary/product-safety-information/cattle-estrous-cycle-and-fda-approved-animal-drugs-control-and-synchronize-estrus-resource-producers
https://www.cargill.co.in/en/heat-detection-in-cattle_-tips-and-techniques#:~:text=The%20cattle%20come%20in%20the%20heat%20after%20every,15-18%20hours.%20Secondary%20signs%20of%20heat%20in%20cattle%3A
https://dairy-cattle.extension.org/what-is-the-basic-estrous-cycle-of-the-cow/