Elsevier

Theriogenology

Volume 77, Issue 5, 15 March 2012, Pages 952-958
Theriogenology

Research article
The reproductive performance of Thoroughbred mares treated with intravaginal progesterone at the start of the breeding season

https://doi.org/10.1016/j.theriogenology.2011.10.001Get rights and content

Abstract

The objective of this study was to investigate the effects of intravaginal progesterone on the reproductive performance of transitional Thoroughbred mares on commercial stud farms. Two hundred twenty-seven (227) non-lactating transitional Thoroughbred mares aged between 4 and 18 y (mean 9.4 ± 3.2 y) located on three stud farms in the Waikato region of New Zealand were used in the study performed during four consecutive breeding seasons (2007–10). Mares were age-matched in pairs and either treated with an intravaginal progesterone releasing device (Cue-Mare, 1.72 g progesterone, 10% w/w) for up to 10 d (Treated; n = 126) or left untreated (Control; n = 101). In both groups, 1,667 iu of hCG was given IV when an ovarian follicle ≥35 mm was detected (in conjunction with estrous behavior) and each mare was bred by natural service. Treated mares were served earlier in the breeding season (mean ± SD interval to first service was 13.9 ± 3.0 vs 26.7 ± 13.2 d for Treated and Control groups, respectively; P < 0.001). In the Treated and Control groups, 95.2 and 42.6% of mares were served within the first 21 d of the season (P < 0.001). Treated mares conceived earlier in the breeding season (mean number of days to conception 37.5 ± 14.2 vs 50.8 ± 21.3 d, P = 0.01). There was no difference between groups in the first service pregnancy rates (53.9 and 50.5% for Treated and Control mares, P = 0.89). Treatment with an intravaginal device increased the number of mares conceiving by the end of the breeding season (91.3 vs 82.3% for Treated and Control groups, P = 0.04). Therefore, this treatment protocol appeared to offer a convenient, economical and reliable method for managing transitional mares on commercial Thoroughbred stud farms.

Introduction

The mare is seasonally polyestrous with regular ovulatory cycles occurring in response to increasing day length [1]. The Thoroughbred breeding season officially commences on September 1 in the southern hemisphere; since there is a desire to breed mares as early as possible in the season, most non-pregnant mares are still in the transition phase from winter anestrus to normal ovulatory estrous cycles [2]. The transition period lasts between 60 and 80 d and is characterized by erratic estrous behavior and the growth and regression of ovarian follicles which fail to ovulate [1], [3].

Several methods have been utilized in an attempt to advance the onset of normal ovulatory estrous cycles in transitional mares. These methods include the use of artificial light exposure commencing several weeks before the start of the breeding season [3], [4], [5] and pharmacologic methods, such as: a) GnRH or its analogues; [6], [7], [8] b) oral progestagens; [9], [10] c) progesterone administered parenterally; [11] d) eFSH administration; [12], [13] and f) dopamine antagonists, such as domperidone or sulpiride [14], [15], [16]. The effectiveness of these methods varies considerably, and in addition, all involve at least once daily administration.

The intravaginal route offers a relatively cheap and convenient method of administering progesterone to mares that avoids the need for daily treatment. Intravaginal devices designed for cattle (CIDR, PRID) have been used off-label in mares and are effective in stimulating follicle growth in transitional mares [17], [18], [19], [20]. Generally, cattle devices have not gained widespread acceptance because clinically they are associated with discomfort and marked vaginitis [18], [21]. We recently reported that treatment of transitional mares with an intravaginal progesterone-containing device specifically designed for mares (Cue-Mare, Bioniche Animal Health Australasia, Victoria, Australia) for 10 d, resulted in follicle growth and ovulation within 4 d of device removal [22], and that the devices were associated with minimal discomfort and vaginitis [23]. Such a treatment therefore offers a potential method of managing the transition period on commercial stud farms.

The aim of this study was to investigate the effects of intravaginal progesterone on the reproductive performance of transitional Thoroughbred mares on commercial stud farms.

Section snippets

Animals

Two hundred twenty-seven (227) non-lactating Thoroughbred mares between 4 and 18 y of age (mean 9.4 ± 3.2 y) located on three stud farms were used. The study was performed during four consecutive breeding seasons (2007–10). All mares remained outside on pasture (consisting of perennial ryegrass) under natural light for the duration of the study and had ad libitum access to water and hay. The study location was the Waikato region of New Zealand (latitude 37°49′ S). Mares were enrolled for

Results

During the treatment period none of the intravaginal devices was expelled. Thirteen mares (10.3%) had the device removed on Day 7 when a follicle ≥ 35 mm in diameter was detected. The remaining mares (89.7%) had the device removed on Day 10. Reproductive outcomes for mare age, farm and year of the study are shown (Table 1).

Discussion

In both the Northern and Southern hemispheres, the Thoroughbred breeding season commences at a time when most non-pregnant mares are in the transition phase from winter anestrus to normal, regular estrus cycles. Early foals are desired because they are generally larger than their later-born peers by the time they are sold at yearling sales at approximately 14 to 17 mo of age [24]. In addition, earlier born foals are more physically advanced than their counterparts when they start racing as

Acknowledgments

Cue-Mare devices were kindly provided by Bioniche Animal Health Australasia Pty, Ltd. The participation of the mare owners and stud managers and their staff is gratefully acknowledged. Funding support for this project was provided by the New Zealand Racing Board through the equine Partnership for Excellence.

References (36)

  • E. Klug et al.

    Advances in synchronizing estrus and ovulations in the mare: A mini review

    J Equine Vet Sci

    (2001)
  • A.M. Smith et al.

    Associations between yearling body measurements and career racing performance in thoroughbred racehorses

    J Equine Vet Sci

    (2006)
  • J. Handler et al.

    Influence of reproductive stage at PRID insertion on synchronization of estrus and ovulation in mares

    Anim Reprod Sci

    (2007)
  • D.D. Turner et al.

    Influence of follicular size on the response of mares to allyl trenbolone given before the onset of the ovulatory season

    Theriogenology

    (1981)
  • J. Cuervo-Arango et al.

    The first ovulation of the breeding season in the mare: The effect of progesterone priming on pregnancy rate and breeding management (hCG response rate and number of services per cycle and mare)

    Anim Reprod Sci

    (2010)
  • O.J. Ginther

    Reproductive Biology of the Mare: Basic and Applied Aspects

    (1992)
  • D.C. Sharp et al.

    Stimulation of follicular activity and estrous behavior in anestrous mares with light and temperature

    J Anim Sci

    (1975)
  • E. Palmer et al.

    Photoperiodic stimulation of the mare during winter anoestrus

    J Reprod Fertil Suppl

    (1982)
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