The incidence of cystic ovarian disorders has been estimated to be 10% with a range among studies between 2.7 to 30% (1,7). There have been several definitions of cystic ovarian disorders. Originally, follicular cysts were defined as follicular structures over 2.5 cm in diameter that persisted for various periods of time without the presence of a corpus luteum (CL). Currently, experts define a follicular cyst as a follicle greater than 17 mm usually accompanied by one or more other large follicular structures and no CL present. (8). Due to the complexity of the disorder and the heterogeneity of the clinical signs, a clear definition is lacking (12). A follicle becomes cystic when it fails to ovulate and persists on the ovary. To further complicate this syndrome is the fact that most follicular cysts are dynamic in that they disappear and are replaced by new cysts or simply disappear with the onset of normal cycles. A smaller percentage of follicular cysts persists and are classified as chronic cysts (2). Thus, accurate diagnosis of cystic ovaries can be a difficult task and is a major challenge to veterinarians. 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 on palpation of the ovaries. Research from Missouri determined that the overall correct diagnosis of the type of cyst was 51% with palpation and 85% using ultrasound. The investigators noted these differences were probably due to the more accurate detection of luteal tissue within the ovary using ultrasonography (6).
Unlike the chronically cystic cows 30 years ago which were in constant or frequent estrus, research data indicates that about 80% of the cows 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. From a management standpoint we must look for health, genetic, or management factors associated with a higher-than-average incidence of cystic ovaries in some herds.
This condition is most common during the first 60 days of lactation when cows experience most health disorders and are under metabolic stress. Several surveys indicate that cows experiencing problems around the time of calving, such as twinning, dystocia, retained placenta and uterine infection, are more likely to develop ovarian dysfunction. (9,10). The appearance of ovarian cysts is more common in older cows. This is interesting because older cows experience a higher rate of periparturient problems. Furthermore, it has been shown that cows over conditioned at dry off were 2.5 times more likely to develop cystic ovaries after calving than herd mates in average condition (9). Since most cysts develop in early lactation, it was 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. There is not much direct evidence of a major genetic component to this condition. There is low to moderate heritability (11).
Each type of cyst, follicular and luteal, requires different hormonal treatments. Manual rupture or aspiration of the fluid from the cyst are less effective. Traditionally gonadotropin releasing hormone (GnRH), or a luteinizing hormone-like product were used to treat follicular cysts and prostaglandin (PG) products were effective for luteal cysts. A single dose of GnRH or hCG followed by PG 7 d later also is a common strategy to treat cysts. Since the standard Ovsynch timed-insemination protocol utilizes both GnRH and PG, this program has been used routinely to treat cystic ovarian conditions.
Recently, the use of progesterone implants (CIDR) along with a PG injection has also been shown to be effective. The question is frequently asked which treatment is most cost effective. A comprehensive study conducted in Florida using 400 cows diagnosed with cystic ovaries compared treatment of cystic ovaries using progesterone treatment (CIDR) with a PG injection given on day 7 when the CIDR is withdrawn to the standard Ovsynch timed insemination program protocol. Cows on the CIDR/PG treatment were observed for estrus and those identified in heat were inseminated. The Ovsynch cows were time inseminated without heat detection. The percentage of cows inseminated using the Ovsynch and CIDR/PG programs were 82% and 44%, respectively. Conception rate (% conceived of those inseminated) and pregnancy rate (% of the total cystic cows in the group that conceived) for cows in the CIDR group were 23% and 9.5%, respectively. Conception rate and pregnancy rate for the cystic cows on the Ovsynch program were 18.3% and 14 %, respectively. There were no statistically significant differences between treatments (3).
However, the cost effectiveness of the treatments must be considered. As a follow-up to that study, a complex economic analysis was conducted using success rates and the costs of treatment (4). The overall results showed the Ovsynch with timed AI protocol for cystic cows provided a $11.39 greater economic advantage per cow than the CIDR/PG/heat detection system (assumed 46% probability of heat detection). If the heat detection rate following the CIDR/PG program improved to 70%, the benefit of the CIDR/PG program improved but was still less than the standard Ovsynch timed AI program. Use of heat detection aids such as tail head marking or activity monitors could improve heat detention rate using the CIDR/PG protocol.
Progress is being made to understand more about the causes of this condition and treatment strategies have improved, but diagnosis of the type of cysts is still a challenge. However, culling chronically cystic cows, developing a strategy to avoid over conditioned dry cows, and providing a balanced transition cow ration will certainly help minimize periparturient problems so that the incidence of cystic ovaries remains low. Implementing best management practices to prevent and monitor calving-related issues such as twinning, dystocia, retained placenta and metritis is critical.
Source: Penn State Extension