Sensitive periods for Ovsynch treatment

Keywords: cow, synchronize, bovine, estrous, estrus, cycle, follicle, wave, Ovsynch

A diagram modified from several sources, showing an estrous cycle with three follicle waves. The physiology of two or three follicle waves is important during “Ovsych” treatment (GnRH-Prostaglandin-GnRH) because it is only those follicles that have already been recruited and already growing in a follicle wave that will ovulate after GnRH treatment; an essential step in re-setting the recruitment of follicles so that a mature follicle will be available for ovulation about 8 to 9 days later. This image shows the periods of time (vertical grey bars) during which follicles can be induced to ovulate by GnRH treatment.

Two and three wave estrous cycles

Key words: bovine, estrous, estrus, cycle, follicle, wave, Ovsynch, prostaglandin

A diagram modified from several sources of two and three wave estrous cycles. One cow has two waves of follicle growth with the follicle in the second wave eventually ovulating. The other has three waves, with the last wave providing the follicle that ovulates. The length of the estrous cycle is one or two days longer in cows that have three follicle waves instead of two. A minority of cows have four follicle-wave estrous cycles.

This physiology is important in everyday dairy practice when prostaglandins are used to shorten the inter-estrous period because follicles are more likely to large and ready to ovulate if cows have more follicle waves during the estrous cycle. There is usually only one follicle per wave but once a follicle has grown to its maximum size it begins to regress, it cannot be utilized. Therefore, many follicles and their oocytes are wasted. The physiology of two or three follicle waves is also important during “Ov-sych” treatment to synchronize ovulation in cattle.

Follicle and a corpus luteum; ultrasound

Key words: wave, bovine, CL, corpus luteum, follicle, cow, ultrasound

Image size: 640 x 480px

A large follicle (the anechoic structure) adjacent to a corpus luteum (CL) in the ovary of a cow; as seen during transrectal ultrasonography. Follicles grow and regress in waves during the bovine estrous cycle. There are commonly two or three waves of follicle growth during the diestrous period. When there are three waves, the estrous cycle is longer (21 to 22 days) than when they are two follicle waves (19 to 20 days). Less commonly,  cows may even have four follicle waves. Therefore the discovery of a large follicle during diestrus (as in this case) does not necessarily mean that a cow is approaching estrus.