Cystic ovarian disease

What it is

In cystic ovarian disease a dominant follicle grows but does not ovulate: the preovulatory surge of luteinising hormone (LH) fails, because the hypothalamus does not respond as it should to the follicle's oestradiol. The follicle keeps growing and persists longer than normal, in the absence of a corpus luteum. The classical definition is an anovulatory structure more than 25 mm in diameter persisting for at least 10 days, although many authors now use smaller diameters.

There are two types, which are extremes of the same process:

• Follicular cyst: thin wall, produces little progesterone; it sometimes secretes oestrogens.
• Luteal cyst: thicker, partly luteinised wall that produces progesterone.

They should not be confused with a cystic corpus luteum, a normal corpus luteum with a central cavity that forms after ovulation and is not pathological.

It is associated with the negative energy balance of early lactation, postpartum diseases and stress. Many cysts that appear in the first weeks after calving resolve on their own.

Who it affects

Mainly high-producing dairy cows in the first months of lactation, more often as the number of calvings increases. It has a hereditary component and is associated with selection for milk yield. A cow that has had cysts in one lactation is at greater risk in the next.

Anatomy involved

• Ovaries: the cyst enlarges the ovary and is palpated per rectum as a fluid-filled structure, larger than a preovulatory follicle, with a thin (follicular) or thicker (luteal) wall. There may be one or several cysts, on one or both ovaries. In the heifer the ovaries lie near the pelvic inlet, and in the multiparous cow they are pulled cranially and ventrally by the weight of the uterus.
• Uterus: without ovulation there is no pregnancy. Palpation and ultrasound of the uterus are part of the examination, to rule out pregnancy and pyometra, other causes of anoestrus, before giving prostaglandin, which can cause abortion.
• In chronic cases with follicular cysts there may be relaxation of the sacrotuberous ligaments, with a raised tail head.

Clinical signs

• Anoestrus: the most common presentation.
• Irregular heats, with short or very long intervals.
• Nymphomania: frequent or continuous heat, with mounting of other cows; uncommon nowadays.
• In chronic cases, a masculinised appearance and relaxation of the pelvic ligaments.
• Many cows are only detected at reproductive examinations, as cows not seen in heat or not becoming pregnant.

Diagnosis

• Rectal palpation: detects an enlarged ovary with a cystic structure and the absence of a corpus luteum, but cannot reliably distinguish a follicular from a luteal cyst.
• Transrectal ultrasound: measures size and wall thickness and looks for a corpus luteum; it is more accurate than palpation.
• Progesterone in blood or milk: low with a follicular cyst and raised with a luteal cyst.
• Repeat examination: to confirm that the structure persists and is not a normal growing follicle.

Treatment and prevention

• Follicular cyst: GnRH (or hCG) to luteinise the cyst, followed a few days later by prostaglandin F2α to remove the luteinised tissue and allow a new cycle.
• Luteal cyst: prostaglandin F2α.
• Ovulation synchronisation protocols with fixed-time insemination, or intravaginal progesterone devices, when the cyst type cannot be determined or to reduce the days to insemination.
• Manual rupture of the cyst is not recommended, because of the risk of haemorrhage and ovarian adhesions.
• Prevention: good transition management to limit negative energy balance, prevention and treatment of postpartum diseases, and regular reproductive examinations to detect non-cycling cows early.

Drug use in food-producing animals is subject to each country's regulations and to withdrawal periods for milk and meat.

Key studies

• Fourichon et al. (2000), meta-analysis of 70 papers on the effect of disease on reproduction in the dairy cow. Ovarian cysts were associated with 6 to 11 more days to first service and 20 to 30 more days to conception. The included studies were observational.
• Nelson et al. (2010), Norwegian national registry with more than 500,000 lactations. Incidence was 0.82% per lactation; it increased with the number of calvings and with autumn calving (HR 2.6 compared with spring), and a cyst in the previous lactation increased the risk. Cows with cysts had more twin births (OR 2.2) and, among culled cows, more culling for reproductive problems (HR 2.1 from the third calving). Diagnoses were recorded in the field, without a common definition.
• Hooijer et al. (2001), 15,562 lactations of Dutch Black and White cows. Incidence was 7.7%, ranging from 1.9% to 11.3% between farms. Heritability was low (0.087 to 0.102), but the genetic correlation with milk, fat and protein yield was positive (0.345 to 0.441): selection for production may increase the frequency of cysts.
• Dinsmore et al. (1987), randomised, double-blind trial in 265 cows with follicular cysts comparing two GnRH analogues. At 30 days the cyst could no longer be palpated in 85% and 89% of cows, with no differences in subsequent fertility. There was no untreated group and diagnosis was by palpation, so the effect of treatment cannot be separated from spontaneous resolution.
• López-Gatius and López-Béjar (2002), randomised trial in 128 cows with ultrasound-diagnosed cysts. Starting treatment with GnRH and cloprostenol together, followed by cloprostenol and GnRH with fixed-time insemination, reduced cyst persistence (10.9% vs 46.9%) and increased ovulation (79.7% vs 17.2%) and pregnancy (28.1% vs 3.1%) compared with the Ovsynch protocol, with a pregnancy rate similar to that of cows without cysts (35.9%). It is a small trial from a single research group.
• Crane et al. (2006), 401 cows with cysts alternately allocated to Ovsynch or to a progesterone device with prostaglandin. 82% and 44% of cows, respectively, were inseminated, but conception (18.3% vs 23.1%) and pregnancy (14.4% vs 9.5%) did not differ. Cows in low body condition responded worse with both protocols. It was carried out in a single herd and allocation was not strictly random.