The effect of follicular wave on fertility characteristics in beef cattle

Abstract

The objectives of this experiment were to determine the effects of follicular wave (first or second) on diameter of the dominant follicle, concentrations of progesterone and estradiol and the hepatic enzymes that inactivate them, thickness of the endometrium, and pregnancy rates to AI. Beef heifers ( = 101) and cows ( = 106) were randomly assigned to 1 of 2 treatments: insemination to the first follicular wave (FFW) or insemination to the second follicular wave (SFW). Estrous cycles of females were synchronized to ensure appropriate timing for the treatments. The MIXED procedure of SAS was used for analysis. A similar proportion of females in each treatment responded to presynchronization; however, females in the FFW group ovulated in response to the first injection of GnRH of the CO-Synch protocol more frequently. Only females ( = 94) that properly responded to ovulation synchronization were included in further analyses. Cows in the FFW group tended ( 0.06) to have larger ovulatory follicles 36 h post-PGF of the CO-Synch protocol compared to cows in the SFW group (14.22 ± 0.42 and 11.83 ± 0.49, respectively), whereas heifers were similar between treatment groups. Three d prior to AI, circulating concentrations of progesterone were lesser ( 0.01) in females in the FFW (3.63 ± 0.80 ng/mL) than in the SFW (7.12 ± 0.83 ng/mL), whereas concentrations of estradiol tended ( 0.08) to be greater in those in the FFW (82.72 ± 6.48 pg/mL) than in the SFW (65.55 ± 6.74 pg/mL). Concentrations of cytochrome P450 1A in the liver were lesser ( 0.01) in females in the FFW than those in the SFW (0.68 ± 0.08 vs. 0.96 ± 0.06, respectively). Endometrial thicknesses were similar between treatments but were thicker ( < 0.0001) in cows (9.73 ± 0.24 mm) than heifers (7.22 ± 0.26 mm). When considering all females or only those that were properly presynchronized, pregnancy rates were similar between treatments. However, when evaluating females that ovulated to the assigned follicular wave, there was a treatment by parity interaction ( = 0.04) with heifers in the FFW having a lesser pregnancy rate (25.9%) than heifers in the SFW (72.0%) while cows in both treatment groups were intermediate (45.4% in FFW and 50.0% in SFW). The differences in concentrations of steroids between treatment groups may affect fertility of heifers; however, additional research is necessary.

Effect of ovarian follicular wave pattern and endocrine characteristics on pregnancy outcome in cows

“…Without taking into account the wave pattern, a higher follicular count favouring pregnancy has been linked to elevated luteal phase P4 concentration (de Lima et al., 2020; Jimenez‐Krassel et al., 2009), which in turn increased the endometrial thickness, interpreted as a better endometrial development favouring pregnancy (Jimenez‐Krassel et al., 2009). To the contrary, unchanged endometrial thickness in spite of higher P4 concentrations is also on record (Muth‐Spurlock et al., 2017).…”

“…The finding is consistent with previous studies citing reduced fertility due to a short luteal phase of ≤14 days after first postpartum ovulation in cows (Breuel et al., 1993; Manns et al., 1983). An extended luteal phase favouring pregnancy was also evinced after P4 supplementation in the cows injected PGF2α in the early to middle part of luteal phase (Xu et al., 1996) as well as the cows inseminated to the ovulation of the second (no P4 supplementation) or the first (P4 supplementation prior to insemination) wave dominant follicle versus the others inseminated to the first wave dominant follicle (no P4 supplementation) (Bisinotto et al., 2010; Denicol et al., 2012; Muth‐Spurlock et al., 2017). It is important to realize that the ovulation, fertilization, embryo transport (Breuel et al., 1993), and most importantly, the age of the ovulatory follicle (Schrick et al., 1993) did not differ between cows with normal and short luteal phases during two or three waves of follicular growth.…”

Consequences of assisted reproductive techniques on the embryonic epigenome in cattle

“…Oocytes within these follicles remain dormant in prophase of meiosis I until recruited to the growing follicle pool. The bovine oestrous cycle is a dynamic process and follicles are recruited in pools and grow together in two or three waves per cycle (Ginther et al 1989;Muth-Spurlock et al 2017). Oocyte growth and maturation occurs concomitant with follicle growth and is regulated by intraovarian oocytegranulosa-theca cell interactions, as well as by autocrine and paracrine molecules such as steroids, growth factors and cytokines (Palma et al 2012).…”

“…Even though fertilisable, the oocytes nursed by the various dominant follicles do not have the same developmental potential. Muth-Spurlock et al (2017) recently compared pregnancy rates in heifers impregnated during the first or second follicular wave and found a 46% increase in pregnancy rate (25.9% vs 72.0%) in females carrying offspring generated as a result of the second follicular wave; however this difference was not observed in cows (45.4% vs 50.0%). Procedures for ART in cattle often include a step of oocyte collection from ovaries (often heifers), either in vivo by superovulation and ovum pickup (OPU) or ex-vivo after slaughter, in which case oocytes from antral follicles of various sizes are collected.…”

The fertility of dairy heifers and cows is not influenced by the follicular wave of the ovulatory follicle

“…Similarly, insemination of FFW lactating dairy cows resulted in a lower pregnancy rate than in lactating dairy cows induced to ovulate follicles from the SFW [18]. Conversely, Muth-Spurlock et al (2017) reported that follicular waves did not affect fertility [19]. Although differences in the characteristics of FFW and SFW ovulatory follicles have been previously demonstrated in dairy [17] and beef [19] breeds of cattle [9,14], the results on the fertility of cattle in these studies are inconsistent.…”