What is Known About Cystic Ovarian Dysfunction?
Posted: March 7, 2004
The majority of ovarian cysts are follicular and a smaller percentage is luteal. Each type of cyst requires a specific hormonal treatment. Studies using either progesterone analysis, ultrasound monitoring of ovarian structures or both methods have consistently shown a significant error rate in distinguishing between follicular and luteal cysts based palpation of the ovaries. Research from North Carolina State University determined that the overall correct diagnosis of the type of cyst was 51% with palpation and 85% using ultrasound. Agreement between both methods was only 57%. The investigators noted these differences were probably due to the more accurate detection of luteal tissue within the ovary in the ultrasonograms. To further complicate this syndrome is the fact that most cysts are dynamic in that they disappear and are replaced by new cysts or simply disappear with the onset of normal cycles. Smaller percentages persists and are classified as chronic cysts. Thus accurate diagnosis of cystic ovaries can be a difficult task.
Unlike the chronically cystic cows 25 -30 years ago which were in constant or frequent estrus, most cows today with a cystic disorder are anestrus -fail to exhibit estrus. There are several theories that attempt to explain the physiological mechanisms responsible for the development of cysts. It is a complex problem. Unfortunately, until these mechanisms are worked out we cannot define a specific cause of the disorder and must look for health, genetic, or management factors associated with a higher than average incidence of cystic ovaries.
This condition is most common during the first 60 days of lactation when cows experience the most health disorders and are under metabolic stress. Several surveys indicate that cows experiencing problems around the time of calving were most likely to develop ovarian dysfunction. These problems include twinning, dystocia, retained placenta and uterine infection. The condition is more common is second and greater lactation cows than younger cows. This is interesting in that older cows experience a higher rate of periparturient problems. Metabolic disturbances due to severe negative energy balance or ketosis were also related to development of cysts. More recently it has been shown that cows over conditioned at dry off were 2.5 times more likely to develop cystic ovaries after calving than herdmates in average condition. In addition, studies have suggested that imbalances of the metabolic hormones insulin and insulin-like growth factors could be causative factors.
Since most cysts develop in early lactation people thought that high production was the major cause of the problem. More recently it has been shown that cows either produce an equal amount or more milk when they are cystic. However, the level of milk was not different from herdmates during the lactation prior to development of the cystic condition. There is not much direct evidence of a genetic component to this condition. However, in Sweden the incidence of cysts decreased from 10.8% in 1954 to 3.3% in 1974 when a policy was established to cull AI bulls if their daughters had an above average incidence of cysts.
We don't know a great deal about this condition and diagnosis of the type of cysts is a challenge. However, culling chronically cystic cows, developing a strategy to avoid over conditioned dry cows and providing balanced transition cow ration will certainly help minimize periparturient problems so that the incidence of cystic ovaries remains low.
Michael O'Connor, Dairy and Animal Science Extension