Pregnancy establishment and maintenance in cattle1

Abstract

A single ovulation, reciprocal embryo transfer study was used to investigate effects of oocyte competence and maternal environment on pregnancy establishment and maintenance in beef cows. Estrous cycles were synchronized in suckled beef cows and embryo donors were inseminated on d 0 (n = 810). Cows were classified on d 0 as having a small (<12.5 mm) or large (≥12.5 mm) ovulatory follicle and randomly chosen as donors or recipients to remove confounding effects of ovulatory follicle size on fertility. Embryos (n = 393) or oocytes (n = 44) were recovered on d 7, and all viable embryos were transferred into recipients (n = 354). All statistical analyses were conducted using the GLM procedure of SAS. Path analysis (with significance set at P < 0.10) was used to examine potential cause-effect relationships among the measured variables. Greater donor cow BW, circulating estradiol concentration at insemination, postpartum interval, and ovulatory follicle size directly increased (P < 0.10) fertilization success. Greater donor cow age was the only factor that directly decreased (P < 0.10) fertilization success. Viability of d-7 embryos was directly inhibited (P < 0.10) by rapid follicular growth rate from d -2 to 0 and heavier BW. Direct beneficial effects to embryo viability were increased serum progesterone concentration on d -2 and ovulatory follicle size. Pregnancy maintenance from d 7 to 27 was enhanced (P < 0.10) by increased serum estradiol concentration on d 0 and progesterone concentration on d 7 in the recipient cow. Increased follicular diameter in the recipient cow on d 0 was detrimental to pregnancy maintenance from d 7 to 27. This manuscript defines the complex interplay and relative contributions of endocrine and physical factors both prior and subsequent to fertilization that influence both oocyte competence and maternal environment and their roles in establishment and maintenance of pregnancy.

Relationship of follicle size and concentrations of estradiol among cows exhibiting or not exhibiting estrus during a fixed-time AI protocol

“…More specifically, estradiol plays a direct role in regulating oviductal secreted glycoproteins [3] and in the regulation of the biological clock in the uterus [4]. Concentrations of estradiol peak approximately 36 h before ovulation [5] and increased preovulatory concentrations of estradiol resulted in increased fertilization success, improved embryo quality and viability [6,7], and a >60% improvement in pregnancy success [8]. Preovulatory concentrations of estradiol also have been reported to influence sperm transport [9], embryo survival [10], and the uterine environment [11][12][13].…”

TRIENNIAL REPRODUCTION SYMPOSIUM: Deficiencies in the uterine environment and failure to support embryonic development1

“…As previously indicated, beef or dairy females induced to ovulate small follicles after ovulation synchronization and dairy cows due to steroid catabolism (Sangsritavong et al, 2002;Vasconcelos et al, 2003) have erroneous endocrine profiles and reduced fertility (Lamb et al, 2001;Lucy, 2001;Perry et al, 2005Perry et al, , 2007. In these steroid deficient animals, previous studies in beef (Mussard et al, 2003a,b;Bridges et al, 2010Bridges et al, , 2012Atkins et al, 2013) and lactating dairy cows (Sartori et al, 2006) indicate that deficient uterine function contributes to this increased occurrence of pregnancy failure. This is not surprising given the numerous functions that estradiol and progesterone have in dictating uterine environment and function.…”

“…Furthermore, Kenyon et al (2012) demonstrated that change in progesterone concentrations from d 0 to 7 was associated with pregnancy outcomes after embryo transfer on d 28, 42, and 63 of gestation and progesterone change from d 7 to 14 was associated with pregnancy outcome on d 28 and 63 of gestation. More recently, Atkins et al (2013) reported that progesterone concentrations at embryo recovery on d 7 after estrus directly influenced embryonic developmental stage. In ovariectomized ewes exogenously treated with steroids, excluding progesterone during early gestation resulted in the recovery of no embryos, reduced uterine protein synthesis, and decreased the ratio of total RNA to total DNA in the uterus .…”

Effects of excess metabolizable protein on ovarian function and circulating amino acids of beef cows: 2. Excessive supply in varying concentrations from corn gluten meal

“…Cows induced to ovulate large follicles have been reported to develop larger CL compared with cows induced to ovulate small follicles (Vasconcelos et al, 2001). As the CL develops from the granulosa and theca cells of the ovulatory follicle, larger follicles tend to have more follicular cells and greater estradiol exposure which influence the developing luteal tissue after ovulation (Atkins et al, 2013). Smaller CL development in MP125 cows was expected after ovulating smaller follicles.…”