Estrus response and fertility after a single cloprostenol treatment in dairy cows with various ovarian structures

Abstract

The objective of this study was to determine rates of estrus and conception in lactating multiparous Holstein cows given 500 μg of cloprostenol intramuscularly after detection of the following ≥ 60 d after parturition: a solid corpus luteum (CL), a CL with a nonechodense cavity ≤ 20 mm in diameter (CLcav), a luteal cyst (cavity > 20 mm in diameter and a luteinized wall > 3 mm in diameter), or a follicular cyst (cavity > 20 mm and a luteinized wall ≤ 3 mm in diameter). The estrus rates were 335/419 (80.0%), 183/223 (82.1%), 170/182 (93.4%), and 44/87 (50.6%), respectively (P < 0.0001), and the conception rates 30 to 36 d after insemination among the estrous cows with an apparently normal mucus discharge were 130/285 (45.6%), 44/141 (31.2%), 39/79 (49.4%), and 19/30 (63.3%), respectively (P < 0.002). Compared with a solid CL, a CLcav did not affect the estrus rate but significantly reduced the conception rate (P < 0.05), and the estrus rates were significantly higher and lower in cows with a luteal or follicular cyst, respectively (P < 0.05).

Introduction

A solid corpus luteum (CL) is present throughout the interovulatory interval in approximately 20% of nulliparous dairy heifers, whereas the remainder have a CL with a nonechodense cavity (CLcav) at least 2 mm in diameter that persists for at least 2 d (1). Most studies have found no differences between cows with a solid CL and those with a CLcav in length of the interovulatory or interestrus interval, plasma progesterone concentration, or pregnancy rate (1–3). However, in 1 study (4), some heifers with a large CLcav (≥ 20 mm in diameter) had a reduced pregnancy rate compared with those that had smaller or no cavities when used as embryo transfer recipients. Apparently there are no reports regarding rates of estrus and conception after treatment with a prostaglandin F2α (PGF_2α) analog in cattle with a CL versus a CLcav.

Anovulatory ovarian structures with a cavity > 20 mm in diameter (usually in the absence of a CL) are defined as ovarian cysts, a follicular cyst and a luteal cyst having a luteinized wall ≤ 3 mm or > 3 mm, respectively, in diameter (5). Although a luteal cyst should have enough luteal tissue that it regresses after treatment with a PGF_2α analog, the general recommendation is that cattle with a follicular cyst be treated with gonadotropin releasing hormone (GnRH) and observed for expression of estrus, which is expected approximately 3 wk after GnRH treatment (5). Alternatively, estrus can be hastened by giving a PGF_2α analog about 10 d after GnRH treatment (5). However, in 1 study (6), in cows with cystic ovarian disease (diagnosed by transrectal palpation), treatment with PGF_2α at cyst diagnosis resulted in significantly higher pregnancy rates 7 and 14 d later than did GnRH treatment at cyst diagnosis. The objective of the present study was to compare rates of estrus and conception in postpartum multiparous dairy cows given 500 μg of cloprostenol (a PGF_2α analog) after detection of a CL, CLcav, luteal cyst, or follicular cyst.

Materials and methods

This research was conducted in accordance with international standards for the use of animals in research and was approved by an institutional animal care committee. The study was conducted between January 2008 and October 2009. Multiparous Holstein Friesian dairy cows (average milk production 8.5 to 9.0 × 10³ kg per cow per year) on 2 Hungarian dairy farms were used.

Transrectal ultrasonographic examinations were done once weekly in all cows starting 20 to 26 d after calving and continuing until approximately 60 d after artificial insemination (AI). For these examinations 2 scanners, 1 with a linear-array transducer of 4.5 to 8.5 MHz (Easi-Scan; BCF Technology, Livingston, Scotland) and another with a linear-array transducer of 6 to 8 mHz (Tringa Linear; Pie Medical Equipment, Maastricht, The Netherlands), were used. Selected ultrasonographic images of the ovaries and uterus were recorded and subsequently reviewed with Echo Image Viewer software (Pie Medical). A CL was defined as a luteinized structure with no visible cavity, whereas a CLcav was defined as a CL with a nonechodense cavity ≤ 20 mm in diameter. Ovarian structures with a cavity > 20 mm in diameter were defined as ovarian cysts, a follicular cyst and a luteal cyst having a luteinized wall ≤ 3 mm or > 3 mm, respectively (5).

The voluntary waiting period was 60 d; thereafter, any cow with no apparent uterine disease (according to transrectal ultrasonography) and an apparently mature CL or CLcav (equivalent to a CL at least 15 mm in diameter) were given 500 μg of cloprostenol (Estrumate; Merck Animal Health, Boxmeer, The Netherlands) intramuscularly. Overall, 419 cows with a CL and 223 cows with a CLcav were treated. In addition, 182 and 87 cows with a luteal or follicular cyst, respectively, at least 60 d after calving and with no apparent uterine disease were similarly treated.

All cloprostenol-treated cows were monitored for estrus, at 1 farm with a pedometer and at the other farm by twice-daily observation (for about 30 min each time), from 1 to 5 d after treatment. Cows designated as being in estrus received thawed semen by AI, approximately 12 h after the onset of estrus. Immediately before AI, the lips of the vulva were parted, and only cows with an apparently physiological, clear, viscous mucus discharge were inseminated; those with a cloudy, purulent, sanguineous, watery, or voluminous vaginal discharge were not inseminated. Pregnancy was diagnosed by ultrasonography 30 to 36 d after AI; cows with an embryo and an embryonic heartbeat were deemed pregnant.

Each farm had its own AI technicians. The ultrasonographic examinations were not conducted by the AI technicians and, for most inseminations, the technician was not aware of the ovarian status of the cow at the time of AI.

The Chi-squared test was used to compare the rates of estrus and of conception among the cows with a CL, a CLcav, a follicular cyst, or a luteal cyst.

Results

The mean interval from cloprostenol treatment to AI was 3.4 ± 1.07 d and did not differ among the groups. The estrus rates varied significantly (P < 0.0001) among the 4 groups of cows; the rate was highest in the cows with a luteal cyst and lowest in the cows with a follicular cyst (Table I). Furthermore, there was a significant difference (P < 0.002) among the 4 groups in the conception rates; the rate was significantly lower in the cows with a CLcav than in the other 3 groups, whose rates did not differ significantly from each other (Table I).

Table I.

Response to a single 500-μg injection of cloprostenol, a prostaglandin F2α analog, in cows with various ovarian structures

	Ovarian structure; % of calves (and proportion)
Measure	CL	CLcav	Luteal cyst	Follicular cyst
Estrus ratea	80.0c (335/419)	82.1c (183/223)	93.4d (170/182)	50.6e (44/87)
Conception rateb	45.6c (130/285)	31.2d (44/141)	49.4c (39/79)	63.3c (19/30)

^aVaried significantly (P < 0.0001) among the groups.

^bBy 30 to 36 d after artificial insemination. Varied significantly (P < 0.002) among the groups.

^c,d,eWithin a row the percentages without a common superscript differed significantly (P < 0.05).

CL — solid corpus luteum; CLcav — CL with a nonechodense cavity ≤ 20 mm in diameter; luteal cyst — cyst with a cavity > 20 mm in diameter and a luteinized wall > 3 mm in diameter; follicular cyst — cyst with a cavity > 20 mm in diameter and a luteinized wall ≤ 3 mm in diameter.

Discussion

In the present study of cows given a single PGF_2α treatment, although the estrus rate was similar for the cows with a CL and those with a CLcav, the conception rate was approximately one-third lower in the latter cows. In previous studies, luteal tissue area (crosssectional area of luteinized tissue) and blood progesterone concentrations did not differ significantly between cows with a CL and those with a CLcav (2,3). However, there are apparently no reports comparing these 2 structures in terms of estrus and conception after treatment with a PGF_2α analog. The cause of the lower conception rate in cows with a CLcav is unknown and warrants investigation.

More than 90% of the cows with a luteal cyst in the present study were found to be in estrus after PGF_2α treatment, consistent with a previous report (7). Remarkably, the estrus rate was significantly higher in these cows than in the cows with either a CL or a CLcav. Although serum progesterone concentrations were not measured in these cows, they are usually lower in cows with a luteal cyst than in those with a CL (6). Furthermore, it is well-established that there is an inverse relationship between the serum progesterone concentration and the diameter of the largest follicle (8) and that there is a “turnover” (replacement over time) of cystic follicles in cows with cystic ovarian disease (9). Although cloprostenol treatment was expected to cause regression of the luteal cyst, presumably at least 1 large viable follicle was recruited to grow and ovulate after the reduction in serum progesterone concentration. Perhaps the combination of moderate progesterone concentrations and a large ovarian follicle promoted expression of estrus. However, from the fact that the conception rate in the cows with a luteal cyst was similar to that in the cows with a CL, we inferred that the ovulatory follicles were generally not persistent follicles, as those are well known to result in reduced fertility because of premature oocyte activation (10).

The estrus rate in the cows with follicular cysts was significantly lower (approximately 50%) than the rate in the other groups of cows, consistent with a previous report that approximately half of cows with plasma progesterone concentrations < 0.5 ng/mL were found to be in estrus within 7 d after treatment with PGF_2α(6). Furthermore, the conception rate for these cows was relatively high. The standard recommendation is that cows with cystic ovarian disease, in particular those with follicular cysts, should be treated with GnRH (5). However, according to the results of the current study, in which the rates of estrus and pregnancy in response to PGF_2α were relatively high, even in cows with follicular cysts, PGF_2α treatment is appropriate, particularly in herds with good estrus detection. In that regard, in cows with cystic ovarian disease, pregnancy rates 7 and 14 d after treatment were significantly higher in cows given PGF_2α than in those given GnRH at the time of cyst diagnosis (6). Furthermore, in cows with ovarian cysts that respond to treatment with PGF_2α, estrus would occur much sooner than if these cows were given GnRH. Therefore, in herds with good estrus detection, perhaps all cows with an ovarian cyst should be given PGF_2α and inseminated when estrus is detected, GnRH treatment being reserved for those in which estrus is not detected.

To maximize the conception rate, only cows deemed to have physiological mucus were inseminated in the current study. The proportion of cows for which insemination was withheld owing to the absence of physiological mucus was approximately 15%, 23%, 54%, and 32% in those with a CL, CLcav, luteal cyst, and follicular cyst, respectively. Although not all cows for which insemination was withheld necessarily had metritis or endometritis, there is an apparent association between postpartum uterine infection and cystic ovarian disease (7).

In summary, cows with a CLcav or a solid CL had similar estrus rates, but the conception rate of the cows with a CLcav was approximately one-third lower than that of the cows with a solid CL. Among the cows with an ovarian cyst, the estrus rate was nearly 50% lower in those with a follicular cyst than in those with a luteal cyst, but the conception rates were not significantly different. These findings were not consistent with the dogma that a CLcav in cattle has no effect on CL function and that treatment with PGF_2α is inappropriate for cows with a follicular cyst.