Follicular Dynamics, Interval to Ovulation and Fertility After AI in Short‐Term Progesterone and PGF2α Oestrous Synchronization Protocol in Sheep

Abstract

The study was aimed to assess the influence that short-term progesterone treatments have on follicular dynamics, oestrus and ovulation in sheep. The treatment was tested thereafter in a field trial to assess its fertility after AI with fresh semen. In a first experiment, 12 ewes without CL were grouped to receive a new (n = 6) or used CIDR (n = 6) for 7 days and blood samples were obtained to follow plasma progesterone profiles. In a second experiment, 39 cycling ewes were synchronized by a 7-day P4+PGF2α protocol using a new (n = 20) or a 7-day used CIDR (n = 19). Half of both groups received 400 IU eCG and half remained untreated as controls. Ultrasound ovarian examination and oestrous detection were used to compare follicular dynamics, oestrus and ovulation in both groups. In a third experiment, 288 ewes in 3 farms were synchronized by the short-term P4+PGF2α+eCG protocol and ewes were AI with fresh semen 24 h after oestrous detection. Lambing performance was used to test the fertility of the treatment. In Experiment 1, ewes with new inserts presented higher P4 concentration than ewes with used inserts throughout the sampling period (p < 0.05) and exhibited a P4 peak at days 1-2 of the treatment that was not observed in ewes with used inserts. In Experiment 2, ewes treated with new and used inserts show similar ovarian and behavioral traits (p > 0.10). However, ewes treated with eCG show shorter interval to oestrus (p = 0.004) and tend to have larger mature CL (p = 0.06). In Experiment 3, oestrous presentation and lambing performance after AI with fresh semen was considered normal compared to published results. Results suggest that the oestrous synchronization protocol based on P4+PGF2α allows little control of follicular dynamics without compromising fertility after AI with fresh semen provided that eCG is added at the end of the treatment.

Characterization of the productive performance of Highlander sheep in Southern Chile. I. Female reproductive traits

“…It is interesting to note that the number of follicles ovulated averaged near 2.0 and that 30/33 (90.9%) of ovulatory-sized follicles at estrus, actually ovulated. In spite of having little relationship between antral follicular functionality and size (Cox et al, 2012), at least as observed in cattle (Geary et al, 2013), the 10% of large follicles that did not ovulate is a relatively small loss when compared to that observed in Suffolk and Texel ewes (>20%, Cox et al, unpublished). The breed was developed for twin lambing to minimize lambing attention (easy-care operation) and to optimize lamb survival, two of the most important economical traits in sheep production (Kleemann and Walker, 2005;Kleemann et al, 2006), therefore by the use of flushing this goal can be met.…”

“…For instance, in small ruminants the administration of gonadotropins for superovulation may induce ovulation of large follicles at any moment after day 5 of the estral cycle (Cameron and Batt, 1991). In addition, estrous synchronization protocols may affect the number of ovulatory follicles, the interval to ovulation and the fertility of ewes depending on the steroidogenic status of larger follicles and may be a reason why eCG at low dosage is effective in controlling the interval to ovulation and fertility of ovulations, but not the number of ovulated follicles (Cox et al, 2012).…”

“…The information was obtained from a sub-group of 541 ewes that were exposed to rams under controlled conditions. Estrus was synchronized by a short-term treatment with a 6-day intravaginal progesterone (0.3 g progesterone, CIDR G, Pfizer) combined with prostaglandin F2␣ (0.125 mg, cloprostenol, Estrumate, Intervet, Friesoythe, Germany) at CIDR removal (Cox et al, 2012). Rams were introduced 24 h after CIDR removal for directed mating in a male to female ratio of 1:8-16.…”

Characterization of the productive performance of Highlander sheep in Southern Chile. II. Male reproductive traits

“…The estrus of the group was synchronized by a progesterone (CIDR G, InterAg, Hamilton, New Zealand) and PGF 2␣ (Cloprostenol, 0.5 mg i.m., Ciclase, Syntex, Argentine) protocol (Cox et al, 2012) combined with estradiol cypionate (ECP, 1 mg i.m., Pfizer, Sao Paulo, Brazil) 24 h after CIDR retrieval. Oestrous detection was confirmed by the tolerance exhibited by ewes to be mounted by a trained-vasectomized teaser that was handcontrolled by an experienced technician.…”

“…Conception rate was defined as the percentage of ewes pregnant after a synchronized estrous compared to those treated. Estrus was synchronized by a short-term treatment with a 6-day intravaginal progesterone (0.3 g progesterone, CIDR G, Pfizer) combined with prostaglandin F2␣ (0.125 mg, cloprostenol, Estrumate, Intervet, Friesoythe, Germany) at CIDR removal (Cox et al, 2012). Rams were introduced 24 h after CIDR removal for directed mating in a male to female ratio of 1:8-24.…”