Ovarian cysts in dairy cattle

Reproductive efficiency is a key driver for profitability on dairy farms.

Many postpartum conditions can impair reproductive performance of dairy cattle and one of the most common ovarian dysfunctions during the postpartum period is ovulation failure, resulting in the materialisation of an ovarian cyst (Opsomer et al, 1998).

Economic losses on dairy farms relating to ovarian cysts are incurred through an extension of calving to pregnancy interval, reported to be 20 to 30 days, and an increase in the risk of culling (Nelson et al, 2010).

Definition

The definition of an ovarian cyst has been described as a large, hard or fluid-filled structure, with a diameter greater than 25mm or more that persists on the ovary for 10 or more days (Youngquist and Threlfall, 2007).

However, in recent years, with the benefit of ovarian ultrasonography, an alternative definition has been considered, defining ovarian cysts as fluid-filled structures with a minimum diameter of 17mm persisting for more than six days in the absence of a corpus luteum and clearly interfering with normal ovarian cyclicity (Silvia et al, 2002). This is based on research suggesting follicles typically ovulate at 13mm to 17mm in diameter (Ginther et al, 2003).

Other definitions include an anovulatory follicle, or follicles greater than 20mm on one or both ovaries that fail to regress yet maintain growth and steroidogenesis, and interfere with normal ovarian cyclicity in the absence of a corpus luteum (Vanholder et al, 2006).

Ovarian cysts are dynamic structures. They can luteinise, regress and may also be replaced by new cysts, and our understanding of whether cysts will luteinise or regress is poorly understood (Jeengar et al, 2014).

Non-steroidogenic or “non-active” cysts that are hormonally inactive do not influence normal ovarian cyclicity and so can occur together with a corpus luteum – and indeed, a pregnancy.

The challenge, as a practitioner examining each cow at a single point in time, is to determine whether the fluid-filled structure greater than 17mm, diagnosed on transrectal ultrasound, has been present for greater than six to 10 days in the absence of a corpus luteum. To assist us, we must investigate the animal’s history and reason for its presentation.

Watson and Cliff (1997) detected ovarian cysts during investigations for anoestrus (58%) and irregular heat (12%) at a negative pregnancy diagnosis (12%) and at a prebreeding examination (17%). From a practical point of view, an ovarian impairment may be suspected when anovulatory follicles are detected no earlier than seven weeks after calving – a time when reproductive functions are thought to be restored (Sheldon and Dobson, 2004).

Ovarian cysts can be identified by transrectal ultrasonography as follicles typically larger than normal ovulatory follicles, with an increased overall ovarian diameter along with a flaccid uterus in the absence of a corpus luteum, while cows in pro-oestrus have an erect turgid uterus. Differentiating from true anoestrus is not difficult because these cows have small ovaries with minimum follicular development.

Ultrasonography assists in distinguishing between follicular and luteinised cysts, and reliable identification of a corpus luteum. A luteal cyst is characterised by enlarged ovaries with one or more cysts with thicker walls (greater than 3mm) than those of thin-walled follicular cysts. Luteal cysts are associated with high concentrations of progesterone (due to their luteal tissue lining), while follicular cysts are associated with relatively low concentrations of progesterone (Jeffcoate and Ayliffe, 1995). Progesterone concentration measurement may also help determine the degree of luteinisation of an ovarian cyst.

Risk factors

A number of cow level risk factors have been identified including body condition score, genetic factors and increasing parity, perhaps resulting due to other conditions that are related to increasing parity – for example, hypocalcaemia. Milk yield has been identified as a risk factor in some studies, but this may be due to the energy status of the cow rather than milk yield per se.

Occurrence of ovarian cysts in lactation has been found to predispose an animal to ovarian cysts in the following lactation. A number of studies have found ovarian cysts to be associated with twinning. Environmental factors including nutrition feeding management, housing type and season have been identified as risk factors (Nelson et al, 2010).

Treatment

Treatments for ovarian cysts are numerous and variable and, in many cases, the decision to treat and the actual treatment undertaken is influenced by many issues, including treatment compliance, the costs of treatment, costs of replacement and the genetic merit of the individual. 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.

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 its 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% (Purohit et al, 2001) and greater if diagnosed prior to 30 days postpartum (Youngquist and Braun, 1986).

Non-hormonal treatments

Manual rupture of ovarian cysts has been suggested in the literature; however, this may result in trauma and haemorrhage causing adhesions and infertility and, as such, cannot be recommended. Transvaginal needle aspiration of ovarian follicular cysts has been described as an alternative to manual rupture; however, a tendency of the cyst to reform has been reported (Lievaart et al, 2006).

Hormonal treatment

There is some degree of thought that practitioners do not need to be able to distinguish between luteal and follicular ovarian cysts as both types respond to similar treatments, with the exception of luteinised cysts where prostaglandin therapy (prostaglandin F2alpha; PGF2alpha) alone is extremely effective. The hormonal treatments outlined hereafter are by no means exhaustive, nor is one recommended above another, but demonstrate a range of successful treatment options.

Gonadotropin-releasing hormone and its analogues

A single gonadotropin-releasing hormone (GnRH) treatment has been the standard treatment for cows with ovarian cysts. After GnRH treatment and subsequent luteinisation of the ovarian cyst, it becomes responsive to PGF2alpha because the steroidogenic synthesis pathways have switched from oestradiol to progesterone. This elevation in progesterone is responsible for restoration of responsiveness to the positive feedback effect of oestradiol, resulting in normal cyclic ovarian activity after the release of endogenous PGF2alpha and cyst regression.

An addition of prostaglandin seven to 10 days after a single treatment of GnRH is routinely used on many farms as a means of resolving ovarian cysts and speeding return to normal ovarian cyclicity; however, a proportion of cows with ovarian cysts have been found to be non-responsive to GnRH treatment (Tebble et al, 2001).

It has been reported that following treatment with GnRH, ovarian cysts may luteinise, but they never ovulate (Gaverick, 1999) and, in many cases, the subsequent corpus luteum found post-treatment form from ovulation of an ovarian follicle and not the existing follicle.

Progesterone

Treatment with progesterone devices disrupts the endocrine environment needed to maintain ovarian follicular cysts by restoring the responsiveness of the hypothalamus to the positive feedback of oestradiol, resulting in normal oestrus and ovulation within seven days after the implant is removed. When using this treatment, some may choose not to treat with PGF2alpha 24 hours before progesterone implant removal; however, the combination of both hormones minimises the risk of incorrect/inefficient treatment if the ovarian cyst was a luteal cyst.

Ovsynch protocol

Protocols for synchronisation of ovulation – for example, Ovsynch – followed by timed artificial insemination performed 16 to 20 hours after the second GnRH infection, have been reported to yield pregnancy rates of 25% in cows suffering from ovarian cysts (Fricke and Wiltbank, 1999).

This treatment is used for ovulation synchronisation on many farms and, to maintain successful ovarian cyst treatment compliance, it is not surprising it is often used for the treatment of ovarian cysts despite an increased cost of treatment. The cost savings are probably made because the farm routine and hormonal treatment regime on set days is not disrupted and the potential is for achieving pregnancy rates as aforementioned.

Summary

Transrectal ultrasonography can assist practitioners in identifying ovarian cysts. In addition, it can also assist in determining whether an ovarian cyst is likely to be “luteal” or “follicular” and, potentially, if the ovarian cyst is “hormonally active or inactive”. A range of treatment regimes are at our disposal to treat ovarian cysts on diagnosis.

Practitioners have a responsibility of monitoring treatment success – a suggested definition for this would be subsequent return to normal cyclicity, insemination and establishment of a viable pregnancy.

Practitioners should monitor and educate clients in environmental and cow-related risk factors.