The period between when a cow calves and when she begins her estrus cycle again is known as the postpartum anestrus interval (PPI). During this interval, the hormonal regulation of the cow must re-establish itself so a normal cycle will progress and she can be bred again.

The duration of postpartum anestrus is affected by both major and minor factors. Controlling some of those factors helps you achieve more success by increasing the pregnancy percentage and shortening your breeding and calving season. The two major factors are:

* Suckling. This probably has the most dramatic effect on PPI. While it is not exactly clear why it occurs, it is evident that the stimulus of a calf nursing a cow has a suppressive effect on the cow's ability to return to estrus after calving. The frequency of nursing also impacts the cow. Cows suckled only once each day tend to have a shorter PPI than cows whose calves suckled regularly throughout the day.

* Nutritional effects. A cow's nutrition and its effects on reproduction are caused by complex interactions of many variables. These include quantity and quality of feed intake, stored nutrient reserves and competition for nutrients by other physiological processes. In general, it can be said that precalving nutrition impacts the length of PPI and postcalving nutrition impacts fertility.
Various management options help to decrease the impact of postpartum anestrus and infertility.

* Restrict the breeding season. This will remove late calving cows with long anestrus periods from the herd.

* Manage nutrition so cows have a body-condition score of 6 before calving.

* Minimize the effects of dystocia.

* Stimulate estrus activity with a sterile male and estrus synchronization systems.

* Judiciously use a complete, partial or short-term weaning system.