RISK FACTORS
The following cow level risk factors have been identified for the development of ovarian cysts:
1.
Genetic Factors. A genetic predisposition exists for ovarian cysts, although the heritability is considered to be low at 0.07-0.12. A genetic correlation between cysts and milk yield has also been established meaning that when specifically selecting for production in the past, producers may have inadvertently also selected for cysts. Selection to reduce the incidence of cystic ovaries in a herd can be successful.
2.
Negative Energy Balance. In early lactation, energy requirements from milk production exceed energy taken in from the diet. This resultant negative energy balance (NEB) results in disruption to the normal hormonal pathways, which can result in the formation of cystic ovaries in some cows.
3.
Body Condition Score. Body condition score (BCS) is used as an indicator of energy balance. Increased incidence of cysts may be seen in animals of lower BCS, however, potentially more important is a severe drop in BCS from calving to peak lactation, rather than the specific score itself.
4.
Parity. Increasing parity is correlated with increasing risk of ovarian cysts, although perhaps this is due to other conditions that are related to age (e.g. milk fever).
5.
Environmental/Management Factors. Any stressors in early lactation can potentially affect the normal resumption of ovarian activity, for example, moving groups, feeding management, housing type and season.
6.
Previous Cases. The occurrence of ovarian cysts in one lactation has been found to predispose an animal to cysts in subsequent lactations.
7. Twinning.
TREATMENT
Treatments for ovarian cysts are numerous and variable and in many cases the decision to treat - and which treatment is used is influenced by many issues, including the costs of treatment, genetic merit of the individual and the cost of replacement heifers. In most instances the success of therapy in terms of disappearance of the ovarian cyst with each of the different hormonal treatments is good, but success measured by achieved pregnancy remains variable across treatments. The benefits of any treatment protocol should be discussed with your vet.
1.
No Treatment. The decision to not treat ovarian cysts is often considered by farmers either as an active decision to cull the cow at the end of her lactation, or in the hope of spontaneous recovery at some stage before a culling decision must be made - spontaneous recovery of ovarian cysts has been reported to be 24% and greater when diagnosed prior to 30 days post-partum.
2. 3.
Non-hormonal treatments. Manual rupture of ovarian cysts is sometimes suggested, however, this may result in trauma and haemorrhage causing adhesions and infertility and as such shouldn’t be recommended.
Hormonal treatment. The priority of treatment is to expose the brain to progesterone, allowing the resolution of normal feedback mechanisms and the resumption of cyclicity. The hormonal treatments outlined are by no means exhaustive, nor is one recommended above another, but demonstrate a range of successful treatment options.
a.
GnRH and its analogues A single GnRH treatment has been the standard treatment for cows with ovarian cysts. This allows the formation of a corpus luteum which produces progesterone, allowing resumption of normal cyclic ovarian activity. However, a proportion of cows with ovarian cysts have been found to be non-responsive to GnRH treatment alone.
b.
Progesterone Treatment with intra-vaginal progesterone devices restore the responsiveness of the brain to the positive feedback of oestrogen, resulting in normal oestrus and ovulation within seven days after the implant is removed. Injecting the cow with prostaglandin 24 hours before the implant removal both synchronises ovulation and the combination of both hormones minimises the risk of incorrect treatment if the ovarian cyst was misdiagnosed as a luteal cyst.
c. Ovsynch protocol
Protocols for synchronisation of ovulation e.g. Ovsynch, including GnRH and prostaglandin injections, followed by timed artificial insemination, have been reported to yield pregnancy rates of up to 25% in cows suffering from ovarian cysts. This treatment is often used for ovulation synchronisation on many farms, so despite the potential increase in drug cost, the costs are potentially negated given that the farm routine and hormonal treatment regime on set days is not disrupted and the potential for achieving pregnancy rates is good.
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