Relationship between follicle size at insemination and pregnancy success

Abstract

Administration of gonadotropin-releasing hormone (GnRH) induces a surge of luteinizing hormone and ovulation in a variety of species, including human beings. Our objectives were to determine the effect of follicle size at the time of ovulation on corpus luteum function and establishment and maintenance of pregnancy in cows in which ovulation was either spontaneous or induced with GnRH. GnRH-induced ovulation of follicles Շ11 mm in diameter resulted in decreased pregnancy rates and increased late embryonic mortality. This decrease in fertility was associated with lower circulating concentrations of estradiol on the day of insemination, a decreased rate of increase in progesterone after insemination, and, ultimately, decreased circulating concentrations of progesterone. In contrast, ovulatory follicle size had no apparent effect on fertility when ovulation occurred spontaneously. Follicles undergoing spontaneous ovulation do so at a wide range of sizes when they are physiologically mature. Therefore, administration of GnRH to induce ovulation likely initiates a preovulatory gonadotropin surge before some dominant follicles attain physiological maturity. GnRH-induced ovulation of follicles that are physiologically immature has a negative impact on pregnancy rates and late embryonic͞fetal survival. These observations in cattle may have implications for assisted reproductive procedures in human beings.ovulation ͉ cattle ͉ artificial insemination ͉ embryonic mortality ͉ fertility P rocedures that control the timing of ovulation in human beings and other mammals are of enormous value in advancing the use of assisted reproductive technologies. In cattle, several protocols are effective at controlling the estrous cycle and reducing the time required to detect estrus (1-3), but the timing of ovulation is imprecise, which makes it difficult to inseminate cows at a fixed time. When fixed-time insemination protocols (protocols that synchronize ovulation) are attempted, gonadotropin-releasing hormone (GnRH) is used to induce ovulation. In some synchronization protocols, GnRH is administered 9 days before insemination to induce ovulation and corpus luteum (CL) formation and to initiate a new follicular wave. Two days before insemination, prostaglandin F 2␣ is administered to induce luteolysis, and 48 h later, GnRH is administered to induce ovulation of the preovulatory follicle (4, 5). Insemination is performed at the time of the second GnRH injection (4) or 16-24 h after the second GnRH injection (5).Bovine follicles achieve ovulatory capacity at Ϸ10 mm in diameter. However, a larger dose of luteinizing hormone is required to induce ovulation of a 10-mm follicle than to induce ovulation of larger follicles (6). In cattle, the efficiency of a single injection of GnRH to induce ovulation and thereby synchronize the initiation of the subsequent follicular wave is only 66% when evaluated across all stages of the estrous cycle (7). Because of this variation in ovulatory response, we hypothesized that considerable variation would e...

Preovulatory follicle diameter, growth rate and time of ovulation during induced oestrus using a CIDR® in trypanotolerant female Bos taurus N’Dama cattle

“…However, reduction in the diameter of the ovulating follicle may be accompanied by progesteronaemia (Sartori and Barros 2011). An increase in the LH effect resulting from the injection of eCG (Sheldon and Dobson 2000;Rostami et al 2011) induces the ovulation of follicles with a smaller diameter (Perry et al 2005). This possibility explains the fact that, in our study, the increase in eCG dose is accompanied by an increase in the percentage of ovulations.…”

“…Thus, after injection of 400 or 600 IU of eCG, the growth rate and diameter of the ovulatory follicle were, respectively, 3.9±0.6 mm/day and 14.5±1.1 mm, and 3.5±0.5 mm/day and 13.9±1.2 mm (Ferreira et al 2013). It does not appear that a reduction in the diameter of the ovulatory follicle is a determining factor for infertility (Sartori et al 2001;Perry et al 2005) as long as a minimal value close to 10 mm is observed (Martinez et al 1999;Sartori et al 2001). Thus, in Senepol cattle (B. taurus) and Nelore cattle (B. indicus), ovulation of the follicle with a diameter less than 8.5 mm is considered as physiological (Sartori and Barros 2011).…”

“…The dominant follicle is capable of ovulating when its diameter is close to 10 mm (Ginther et al 1996;Sartori et al 2001). In heifers and beef cattle, the success of artificial insemination depends on gestation rates, which are themselves significantly influenced by the size of the follicle which has ovulated (Perry et al 2005(Perry et al , 2007Meneghetti et al 2009). Maximising the size of the preovulatory follicle and the integrity of the ovocyte is therefore an important objective of reproductive hormonal management programmes which use systematic insemination (Wiltbank and Pursley 2014).…”

Fixed-time AI pregnancy rate following insemination with frozen-thawed or fresh-extended semen in progesterone supplemented CO-Synch protocol in beef cows

“…Our previous CO-Synch-CIDR study, with an interval of 64 h between the PGF2 α and the second GnRH treatment, resulted in an acceptable fixed-time AI pregnancy rate [9]. This interval should diminish ovulation of immature, low estrogen-producing follicles, and result in the development of a competent corpus luteum [10,11]. The CO-Synch protocol is a commonly used protocol due to minimal handling and acceptable pregnancy rates; hence, it was used in this study.…”

Mathematical analysis of a model for the growth of the bovine corpus luteum

“…While the role of ovarian physiology and, in particular, CL growth, development and function have been the main focus of many experimental studies (Lucy, 2001;Mann and Lamming, 2001;Perry et al, 2005;Robinson et al, 2006), mathematical modelling of this biological aspect is scarce. Existing models have focused on hormone production and its regulation during the bovine oestrous cycle (Boer et al, 2011;Pring et al, 2012), while Meier et al (2009) concentrated on progesterone production.…”