Follicle Development during Luteal Phase and Altrenogest Treatment in Pigs

Abstract

Synchronization of the oestrous cycle of gilts using altrenogest treatment has been found to increase ovulation rate. The current experiment investigated if the increase in ovulation rate after altrenogest treatment is related to increased follicle size at the end of altrenogest treatment compared with late luteal phase follicles. Crossbred gilts (n = 15) received altrenogest during 18 days [20 mg Regumate (Janssen Animal Health, Beerse, Belgium)], starting 5-7 days after onset of first oestrus. Control gilts (n = 15) did not receive altrenogest. At days 10-12 of the oestrous cycle [i.e. in the presence of corpora lutea (CL)], average follicle development was 2.51 +/- 0.20 mm (assessed with ultrasound) in altrenogest-treated gilts and 2.58 +/- 0.16 mm in control gilts (p > 0.10). During the last days of altrenogest treatment (i.e. when CL had gone into regression), average follicle size had increased to 3.01 +/- 0.31 mm (p < 0.05). Subsequent ovulation rate was 16.6 +/- 1.7 in altrenogest treated gilts and 15.1 +/- 1.2 in control gilts (p < 0.05). Altrenogest treatment resulted in increased follicle size after regression of the CL, showing that suppression of follicle growth by altrenogest alone is less severe than suppression by endogenous progesterone (either with or without altrenogest). Altrenogest treatment also resulted in a higher ovulation rate. However, it is unclear if the increased follicle size and higher ovulation rate after altrenogest treatment are causally related, as the relation between the two on an animal level was not significant.

Progestin Exposure Before Gonadotropin Stimulation Improves Embryo Development after In Vitro Fertilization in the Domestic Cat1

“…The most common postulated reason is that a down-regulated ovary is more sensitized and likely to produce a uniform follicular response to gonadotropin(s) in the gonadotropin-sensitive early antral phase of development. Therefore, a hormonal stimulus (either endogenous or exogenous) is better able to recruit a cohort of follicles of similar stage, thereby enhancing synchronized antral growth and ovulation of best quality oocytes [1,53]. Data from our study confirmed that a similar effect occurs in domestic cats that are down-regulated using progestin or a GnRH antagonist.…”

“…Most of the literature attributes the success of these agents to ovarian suppression or synchronization alone, specifically the synchronized recruitment of a cohort of follicles that are stimulated in an early gonadotropin-responsive stage or that develop and ovulate predictably [1]. However, it is increasingly clear that progestin exposure induces complex changes in the ovary that are not attributable to ovarian quiescence alone.…”

“…Exogenous progestins have been used extensively to control and synchronize ovarian cycles for assisted breeding in many domestic species and nondomestic ruminants, but little research has focused on the question of how progestin exposure improves ovarian response [1][2][3][4]. Most of the literature attributes the success of these agents to ovarian suppression or synchronization alone, specifically the synchronized recruitment of a cohort of follicles that are stimulated in an early gonadotropin-responsive stage or that develop and ovulate predictably [1].…”

Effects of Breeding at the Second Oestrus or After Post‐Weaning Hormonal Treatment with Altrenogest on Subsequent Reproductive Performance of Primiparous Sows

“…The duration of progestagen treatment that produces optimal productivity in primiparous sows is still uncertain since good results could be obtained when altrenogest was used for 3-7 days (Kirkwood and Smith 1986;Martinat-Botte´et al 1994;Ferna´ndez et al 2005;Everaert et al 2007), 12 days (Koutsotheodoros et al 1998) or for 18 days (Davis et al 1979;Martinat-Botteé t al. 1995;Soede et al 2007). In contrast, more multiparous sows were bred within 10 days after altrenogest treatment for 14 compared to 7 days (Patterson et al 2008).…”

“…2007). Nevertheless, follicle development can be less suppressed with the recommended dosage of 20 mg/day of altrenogest than under endogenous progesterone, thereby increasing the risk of cystic follicle development (Soede et al. 2007).…”