Ovarian follicle dynamics in ewes treated with intra-vaginal progesterone pessaries. 2. Factors affecting timing of estrus and reproductive outcomes following artificial insemination

Walker, S.K.; Kelly, Jennifer M.; Hebart, M. L.; Swinbourne, Alyce M.S.; Weaver, Alice C.; Kleemann, David O.

doi:10.1016/j.theriogenology.2023.03.008

Cited by 3 publications

(5 citation statements)

References 14 publications

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“…This response to PGF2α treatment supports the expectation (Walker, Kelly, Hebart, et al, 2023) that improved AI outcomes are likely if ovulatory follicles emerge within the days 7 to 9 period of pessary treatment. The improvement in fertility occurred without a detectable change in the pattern of oestrus indicating that it resulted from enhanced oocyte quality.…”

Section: Discussionsupporting

confidence: 83%

“…Comparable results have been reported in earlier studies (Ali, 2007;Payan et al, 2022). This improvement supports the hypothesis (Walker, Kelly, Hebart, et al, 2023) that young ovulatory follicles in the breeding season are less well developed compared with the non-breeding season and more likely to respond positively to earlier eCG treatment. In that study, young follicles in the breeding season were associated with a later and more variable onset of oestrus whereas, in the non-breeding season, they were associated with an earlier and less variable onset of oestrus.…”

Section: Ta B L Esupporting

confidence: 87%

“…The day 7 to 9 period is immediately before the mean day of emergence of ovulatory follicles in naturally cycling sheep (11.4 ± 0.46 days) and marginally later than the overall figure obtained in ewes treated with pessaries (7.5 ± 0.48 days) (Walker, Kelly, Swinbourne, et al, 2023). Little is known of the characteristics of ovulatory follicles that emerge in this period although they are larger when measured on day 12 compared with other days (Walker, Kelly, Hebart, et al, 2023). Given this response to treatment on day −27, it is surprising that treatments at other times (day −12 and/or day +6) did not also improve reproductive outcomes.…”

Section: Discussionmentioning

confidence: 99%

“…Treatment of ewes with intravaginal progesterone pessaries (Robinson, 1965) and equine chorionic gonadotrophin (eCG; Gordon, 1983) facilitates synchrony of oestrus in fixed‐time AI programs. Reproductive success following treatment during the breeding season is influenced by the age of the ovulatory follicle which is determined primarily by the time of luteolysis (Evans et al, 2001; Flynn et al, 2000; Walker, Kelly, Hebart, et al, 2023). In the presence of a pessary, these follicles emerge but do not ovulate and, consequently, range in age from 1 to 14 days at pessary removal (Evans et al, 2001; Johnson et al, 1996; Walker, Kelly, Hebart, et al, 2023).…”

Section: Introductionmentioning

confidence: 99%

“…The most fertile sheep are those in which ovulatory follicles emerge between days 7 and 9 of the pessary period (Walker, Kelly, Hebart, et al, 2023). The least fertile are those that emerge after day 9 whilst ewes in which emergence occurs before day 7 are of intermediate fertility.…”

Section: Introductionmentioning

confidence: 99%

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Strategies to improve the success of fixed‐time artificial insemination in the ewe

Weaver

Kelly

Swinbourne

et al. 2023

Reprod Domestic Animals

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During the sheep breeding season, ovulatory follicles vary widely in age at pessary removal impacting both the timing of oestrus and pregnancy rates following artificial insemination (AI). Ovulatory follicles that emerge between days 7 to 9 of the pessary period are associated with higher fertility whilst those that emerge earlier or later are associated with lower fertility. In this study, two strategies to improve the success of AI by controlling the development of the ovulatory follicle were examined. In the first, ewes were treated with PGF2α at either −12 and/or +6 days (experiment 1) or −27 days (experiment 2) relative to pessary insertion to control the time of emergence of the ovulatory follicle. In the second, ewes were treated with eCG (400 IU per ewe) at either 0 h, −6 h or −12 h relative to pessary removal (experiment 3) to improve the development of young ovulatory follicles. PGF2α administered on day −27 increased the percentage of pregnant ewes by 17.8% and the number of foetuses per 100 ewes inseminated by 33.9%. PGF2α treatment at other times had either no effect or reduced fertility. During the breeding season, treatment with eCG at −12 h improved the synchrony of oestrus, reduced the size of the ovulatory follicle but did not improve pregnancy rate compared with other treatments. Treatment had no effect during the non‐breeding season, supporting earlier findings that the quality of young ovulatory follicles differs during the year. In conclusion, PGF2α treatment 27 days before pessary insertion provides a new and cheap strategy to improve the success of fixed‐time AI programs.

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Section: Discussionsupporting

confidence: 83%