How Do You Tell When A Cow Or Heifer Is In Estrus?
• Chart depicting hormone levels of estous activity in cattle Day 0 – Standing heat. Increased levels of estrogen are produced by a maturing follicle in the cow’s ovaries. Secretions along the reproductive tract allow for easier breeding and aid for sperm to travel through the uterus to the ovum. Standing heat usually lasts for 12 to 24 hours, after which ovulation occurs. • Ovulation. The mature follicle ruptures and the ovum travels through to the fallopian tube where it awaits the arrival of the sperm. Ovulation occurs in response to a surge of Luteinizing Hormone (LH) from the pituitary gland in the cow’s brain. Ovulation occurs 12 hours after the cow goes out of heat. • Days 1 and 2 – Alteration of cells that line the Follicle. These cells regenerate and grow to create the corpus luteum (CL) in the area where the mature (now dead) follicle had ruptured and release the ovum. • Days 2 to 5 – Growth of the Corpus Luteum. The growing CL produces high levels of progesterone which cause
