Managing Reproductive Disorders in Dairy Cows

 

Ovarian Cysts

For the purpose of this review, ovarian cysts are defined as anovulatory fluid-filled structures 25 mm in diameter that persist on the ovaries for more than 10 days (Archibald and Thatcher, 1992). Ovarian cysts in dairy cows have been reported to be a major cause of economic loss and reproductive dysfunction in dairy operations (Garverick, 1997), and cows diagnosed with cysts often exhibit extended calving intervals (Bartlett et al., 1986). The reported incidence of ovarian cysts in dairy cows varies from 10 to 13% (Erb and White, 1973; Bartlett et al., 1986), and problem herds may have a much greater incidence (30 to 40%) for brief periods (Archibald and Thatcher, 1992). Based on these incidence rates, ovarian cysts probably affect at least one million dairy cows in the United States each year (Garverick, 1997).

 

Classification of Ovarian Cysts

Ovarian cysts can be classified as either follicular or luteal (Table 1). Follicular cysts are thin-walled, fluid-filled, ovarian structures 25 mm in diameter. Many cows exhibit more than one cystic structure on one or both ovaries at any given time. Early studies reported that cows with cysts exhibited intense and prolonged estrual behavior termed nymphomania (Kessler and Garverick, 1982) resulting from low progesterone due to the absence of a functional CL and increased estradiol from the cystic follicle. Normally, estradiol from a preovulatory follicle initiates a cascade of endocrine events that induce ovulation. In the case of cystic follicles, this endocrine cascade is uncoupled, and normal progression of the estrus cycle is disrupted causing infertility. The etiology of follicular cysts also is difficult to study because of the unpredictability of the onset of cyst formation within an individual cow (Garverick, 1997). The precise mechanism responsible for this endocrine uncoupling is poorly understood.

Luteal cysts are thick-walled, fluid-filled structures 25 mm in diameter that secrete normal to above normal amounts of progesterone. Most luteal cysts probably form through luteinization of a follicular cyst (Garverick, 1997) and can cause infertility if they persist and maintain systemic progesterone at concentrations that inhibit the LH surge and ovulation. The thick wall of luteal cysts is composed of luteal tissue and, in contrast to cystic follicles, the fluid-filled cavities of cystic CL often contain numerous intertwining trabecula that can be easily resolved using ultrasonography. Luteal cysts should not be confused with normal CL containing a fluid-filled cavity. Based on ultrasonographic examinations in heifers, 79% of otherwise normal CL contain cavities ranging from less than 2 to greater than 10 mm in diameter at some time during the estrous cycle and early pregnancy (Kastelic et al., 1990).

Based on recent field research using ultrasound to monitor follicular development in lactating dairy cows (Fricke et al., unpublished), a new classification of follicular cysts may predominate in lactating cows (Table 1). These cysts appear similar to follicular cysts using ultrasound, but do not inhibit normal progression of follicular waves and ovulation of normal dominant follicles. Therefore, cows exhibiting this type of cystic structure do not normally exhibit nymphomania. Because these cysts do not impair normal reproductive function, we have termed them benign follicular cysts. The presence of benign follicular cysts may complicate both diagnosis and treatment of follicular cysts in lactating dairy cows.

 

Table 1. Classification, functional status, and response to GnRH or PGF2a of ovarian cysts in dairy cows.

Classification

Steroid Secreted

Response to GnRH

Response to PGF2a

Follicular

Estradiol

Luteinization

None

Luteal

Progesterone

None

Regression

Benign Follicular

None

None

None

 

Risk Factors and Nutritional Factors Affecting Ovarian Cysts

The physiology and etiology of ovarian cysts is poorly understood, and there is much conjecture regarding risk factors for ovarian cysts. Heredity has been implicated, however, heritability estimates are low (Casida et al., 1951; Ashmaway et al., 1990), and selection against cysts is probably not a profitable management strategy for dairy producers (Garverick, 1997). Other factors include increased milk production (Johnson et al., 1966), estrogen content of forages (Barga, 1987), and uterine infections (Bosu and Peter, 1987; Peter et al., 1989). Garverick (1997) has also suggested that compounds with estrogenic activity in feedstuffs may play a role in cystic ovarian disease. Zearalenone is a mycoestrogen produced by the fungi Fusarium spp. that may be present in moldy feed (Diekman and Green, 1992). Zearalenone adversely affects fertility in swine and, although cattle are not as sensitive to its effects, it should be limited to less than 500 ppb in the total diet DM (Whitlow and Hagler, 1993).

Cows with excessive body condition at dry off are 2.5 times more likely to develop cystic ovaries (Gearhart et al., 1990), and the incidence of cysts for cows that were normal and over-conditioned during the dry period were 12% and 29%, respectively (Butler and Smith, 1989). However, in some studies the over-conditioning of cows at calving has not been associated with development of ovarian cysts (Gearhart et al., 1990; Ruegg et al., 1992). Risk of ovarian cysts also increases in primiparous cows with elevated milk ketone concentrations (Odds Ratio = 8.7; Andersson et al., 1991). Harrison et al. (1984) reported cystic ovary incidence rates for cows fed a selenium deficient diet during the dry period of 50% for control cows versus 19%, 44%, and 19%, respectively, for cows supplemented with selenium, vitamin E, or selenium/vitamin E. Feeding 300 mg b-carotene per cow daily from days 3-98 postpartum did not influence the incidence of cystic ovaries or reproductive performance (Wang et al., 1988). Control and treated cows were supplemented with 75,000 IU vitamin A per cow per day. There was no reproductive benefit to feeding 1,000,000 IU versus 100,000 IU vitamin A per cow per day (Tharnish and Larson, 1992). The current practice on commercial dairies is to supplement dry cows and lactating cows with vitamin A at about 100,000 IU and 150,000 IU per cow per day, respectively (Weiss, 1998).

Diagnosis and Treatment of Ovarian Cysts

Diagnosis of cysts in dairy cattle most often occurs during routine postpartum rectal examinations conducted by a bovine practitioner. Palpation per rectum of a large, fluid-filled structure is commonly used as a clinical indication of a follicular cyst. Unfortunately, differentiation between follicular and luteal cysts via rectal palpation is difficult, even for experienced practitioners (Dawson, 1975; Farin et al., 1992). Accuracy of diagnosis increases when using transrectal ultrasonography, with correct identification of greater than 90% of luteal and nearly 75% of follicular cysts (Farin et al., 1990, 1992). Follicular and luteal cysts also can be classified based on serum progesterone concentrations (Farin et al., 1990). Diagnosis of a cyst in conjunction with low serum progesterone is indicative of a follicular cyst, whereas a cyst in conjunction with high serum progesterone is indicative of a luteal cyst. Using these criteria, benign follicular cysts would fall into either category depending on the stage of the estrous cycle when they were detected.

Treatment for ovarian cysts depends on the classification of the cyst (Table 1). Follicular cysts are most commonly treated by administration of synthetic GnRH analogs approved for use in lactating dairy cows (Bierschwal et al., 1975; Seguin et al., 1976; Whitmore et al., 1979). Manual rupture of cysts via rectal palpation is not recommended because of the reduced efficacy compared with GnRH (Ijaz et al., 1987) and because adverse side effects including adhesions around the ovary and adnexa may impair fertility (Archibald and Thatcher, 1992). Interestingly, approximately 20% of untreated cows with follicular cysts recover spontaneously (Bierschwal et al., 1975), supporting the notion that many of these cysts may indeed be benign. Treatment with GnRH induces luteinization rather than ovulation of the follicular cyst, and ultimately results in formation of a luteal cyst (Garverick, 1997; Fricke et al., unpublished observation). Once formed, regression of a luteal cyst can be induced by administration of PGF2a (Nanda et al., 1988). Administration of GnRH to cows with benign follicular cysts often induces ovulation of a normally growing dominant follicle rather than the cyst itself (Fricke et al., Table 2), and other researchers have reported similar observations (Archibald and Thatcher, 1992; Garverick, 1997).

 

Table 2. Effect of ovarian cysts on synchronization rate and conception rate in lactating dairy cows after synchronization of ovulation using Ovsynch.

 

Ovarian cysta

 

Item

Yes

No

Overall

Incidence

11.0%

89.0%

 

Synchronization rateb

73.1%

85.3%

84.0%

Conception ratec

36.8%

48.8%

47.6%

aA fluid-filled ovarian cyst 25 mm in diameter present at the time of the second GnRH injection of the Ovsynch protocol.

bOvulation of a normal dominant follicle after the second GnRH injection of the Ovsynch protocol.

cUltrasonographic determination conducted at 28 d post AI.

 

The ideal treatment for ovarian cysts would be effective for all three classifications of ovarian cysts. Ovsynch, a protocol for synchronizing ovulation in lactating dairy cows, uses injections of both GnRH and PGF2a (Pursley et al,. 1995, 1997), and may be an effective treatment for ovarian cysts (Table 2). A recent field trial using Ovsynch and ultrasonographic monitoring of ovarian structures (Fricke et al., unpublished) revealed that 11% of lactating cows exhibited a large ovarian structure that would have been diagnosed as a cyst using rectal palpation. Treatment with Ovsynch induced ovulation of a follicle other than the cyst that was present at the time of the second GnRH injection in 73% of cows. Nearly 37% of these synchronized cystic cows conceived after a timed AI. These preliminary data support use of Ovsynch as a treatment for cows exhibiting all classifications of ovarian cysts and may be the treatment of choice when rectal palpation is used to diagnose cysts.

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