Fertility in the cow-calf herd is the most valuable trait fourfold.
First, the hypothalamus and pituitary glands at the base of the brain are essential components of the reproductive process. We should always remember that those glands in the back of the mind are the control center for the “business end” of the cow.
The ovary is responsible for two main functions. The ovary is responsible for producing the unfertilized egg called the ovum and for producing estrogen and progesterone. Each heifer or cow should have two ovaries, one sitting on the end of each oviduct. The production of an ovum is initiated by a hormone from the hypothalamus called GNRH that triggers the pituitary gland to release follicle- stimulating hormone (FSH) and luteinizing hormone (LH). Normally, when FSH and LH act on the ovary, it causes the ovulation of an ovum.
An ovum will migrate toward the oviduct and a corpus luteum will develop at the site of ovulation. The corpus luteum is responsible for producing the hormone of pregnancy known as progesterone. If no pregnancy is detected within the uterus on days 16-18 from the previous ovulation, the corpus luteum will regress, and estrogen will initiate a new heat.
Using hair-like structures, the funnel-shaped opening to the oviduct catches the egg for migration toward the middle of the oviduct, toward the site of fertilization. If the ovum becomes fertilized, the new embryo will still be migrating in the oviduct for a few days. This is a valuable reason to avoid moving or transporting cows that are potentially short-bred less than eight days, particularly. It is generally best to limit moving and handling within 30 days of breeding. Proper stewardship (nutrition, disease control) and handling are essential for helping to maintain pregnancy.
A fertilized egg continues its movement through the oviduct into the adjoining uterine horn. Within the 18-day window of ovulation, the fertilized embryo is developing its home base in the uterine horn. This is understood to occur through a process of maternal recognition of embryonic signaling that goes on between the embryo and the mother’s uterine tissue.
A basic understanding of cattle reproduction can help improve management outcomes for enhanced reproductive efficiency. 
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Jason Duggin
- Beef Extension Specialist
- University of Georgia
- Email Jason Duggin
