Progress 09/01/06 to 08/31/11
Outputs
OUTPUTS: In cattle, fertilization generally occurs following greater than 90% of matings, but pregnancy rate at the earliest possible detection (day 27) is generally less than 70%. Cows induced with gonadotropin releasing hormone (GnRH) to ovulate smaller follicles have reduced pregnancy rates and experience greater embryonic loss, even after pregnancy has been established. These inefficiencies are likely due to either ovulation of an immature oocyte that compromises fertilization and embryo survival or ovulation occurs before the follicular cells have fully matured to produce sufficient estradiol and subsequently, progesterone to adequately prepare the uterus for pregnancy. Below we describe a reciprocal embryo transfer study designed to differentiate between follicular effects on oocyte quality and uterine environment on pregnancy success in beef cattle following GnRH-induced ovulation. We used path analysis to describe relationships among the complex array of factors affecting pregnancy success. Single embryos (n = 394) were recovered from donor cows (day 7) and all live embryos were transferred into recipient cows on the same day. Donor and recipient cows were classified as ovulating either a small (less than 12.5 mm) or large (greater than or equal to12.5 mm) diameter follicle and transfers occurred in a 2x2 factorial arrangement of these categories. Greater donor cow weight, circulating estradiol concentration at the time of GnRH-induced ovulation and artificial insemination (day 0), days since calving, and ovulatory follicle size (in order of importance) directly increased fertilization success. Embryo survival on day 7 was greater in cows with increased serum progesterone concentration on day -2 and cows that ovulated larger follicles. Interestingly, increased ovulatory follicle size was the only factor that directly improved embryo quality on day 7. Embryo survival in recipient cows from day 7 to 27 was enhanced by increased circulating estradiol concentration on day 0 and progesterone concentration on day 7 indicating that these hormones helped prepare the uterus for a successful pregnancy. Increased ovulatory follicle diameter in the recipient cow on day 0 was detrimental to embryo survival from day 7 to 27, which we interpret to mean that the corpus luteum that forms on the ovary after ovulation of a large follicle may be inherently shorter lived allowing less time for the embryo to produce its obligatory pregnancy recognition signal, interferon tau. Successful establishment of pregnancy depends on the complex interplay of endocrine and physiological factors both prior and subsequent to fertilization by influencing both oocyte competence and maternal environment. Increased serum estradiol (day 0) and subsequent progesterone (day 7) concentrations are direct effects of ovulatory follicle size, thus, it appears that increased fertility in cows ovulating larger follicles is mediated through increased estradiol and progesterone production and their effects on the maternal environment. The data demonstrate the numerous variables that contribute to successful establishment of pregnancy. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
A long term objective of this research is to determine the effect the physiological status of an ovulatory follicle on the establishment and maintenance of pregnancy in beef cows. More specifically, identification of factors affecting the development of a competent oocyte and(or) a uterine environment that is conducive to pregnancy may result in improved pregnancy rates following synchronized ovulation in beef cows. The data provided herein demonstrate the numerous variables that contribute to successful establishment of pregnancy. In particular, increased estradiol at the time of insemination and increased secretion of progesterone after insemination in cattle is critically important to fertility and embryo survival. Management strategies that promote the physiological maturity of a dominant follicle prior to synchronization of ovulation should increase pregnancy rates and reduce late embryonic/fetal mortality following insemination at a predetermined time.
Publications
- Atkins, J.A., Geary,T.W., and Smith, M.F. (2008). Factors associated with ovulatory follicle growth rate and diameter in postpartum beef cows. J. Anim Sci 86 (E-Supplement 2):W170.
- Atkins, J.A., Smith, M.F., MacNeil, M.D., and Geary, T.W. (2009). Determinants of embryo development and quality in beef cattle: Effect of pre-ovulatory follicle size, CL volume, and serum concentrations of progesterone. Biology of Reproduction (Supplemental ) p 162.
- Atkins, J.A., Smith, M.F., and Geary, T.W. (2010). (Invited ASAS Animal Science Young Scholar) Factors affecting Ovulatory follicle size, embryo quality and pregnancy in suckled beef cows. J. Anim Sci (E Suppl 3) 88:82
- Atkins, J.A., Smith, M.F., MacNeil, M.D., Jinks, E.M., and Geary, T.W. (2010). Contributions of follicle size to establishment and maintenance of pregnancy in suckled beef cows using reciprocal embryo transfer. Proceedings 8th International Ruminant Reproduction Symposium. p117.
- Jinks, E.M., Atkins, J.A., Pohler, K.G., Smith, M.F., Perry, G.A., MacNeil, M.D., and Geary, T.W. (2010). Factors affecting preovulatory concentrations of estradiol and its role in establishment and maintenance of pregnancy in suckled beef cows using reciprocal embryo transfer. Proceedings 8th International Ruminant Reproduction Symposium. p118.
- Pohler, K.G., Atkins, J.A., Jinks, E.M., Johnson, C.L. Smith, M.F. Green, J.A., MacNeil, M.D., and Geary, T.W. (2010). Circulating concentrations of pregnancy associated glycoproteins (PAGs) are associated with embryo/fetal survival but not ovulatory follicle size in suckled beef cows. Proceedings 8th International Ruminant Reproduction Symposium. P119.
- E. M. Jinks, Pohler, K.G., Smith, M.F., MacNeil, M.D., Roberts, A.J., Waterman, R.J., and Geary, T.W. (2011) Effect of ovulatory follicle size and estradiol supplementation during the preovulatory period on pregnancy rates in postpartum beef cows. Annual Meeting of the Society for the Study of Reproduction. Reproduction and the World's Future. Abstract #479. Portland, Oregon
- Atkins, J.A., Smith, M.F., Wells, K.J., and Geary, T.W. (2010). Factors affecting preovulatory follicle diameter and ovulation rate after gonadotropin-releasing hormone in postpartum beef cows. Part I: Cycling Cows. J Anim Sci 88:2300-2310.
- Atkins, J.A., Smith, M.F., Wells, K.J., and Geary, T.W. (2010). Factors affecting preovulatory follicle diameter and ovulation rate after gonadotropin-releasing hormone in postpartum beef cows. Part II: Anestrous Cow. J Anim Sci 88:2311-2320
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Progress 09/01/09 to 08/31/10
Outputs
OUTPUTS: Previous research indicates cows ovulating a small dominant follicle (≤ 12 mm) had lower pregnancy rates than cows ovulating a large follicle (> 12 mm). We hypothesized cows ovulating a small follicle would have delayed embryo development and decreased embryo quality. Objectives of this study were to determine 1) the relationship between follicle size at GnRH-induced ovulation, CL volume, and serum concentrations of progesterone (P4) 7 d later and 2) effects of ovulatory follicle size, CL volume, and P4 on embryo stage and quality 7 d after AI. Lactating multiparous beef cows (n=931; 644 donor and 287 recipient cows) were synchronized for single ovulation embryo transfer (d7) with the CO-Synch protocol (GnRH1 on d-9, PGF2α on d-2, and GnRH2 with timed AI on d0). Diameter of the ovulatory follicle (d0), CL, and lumen of the CL (d7) were determined using transrectal ultrasonography. The functional CL volume was calculated by subtracting the lumen volume from the total CL volume. Embryos recovered from donor cows were assessed for stage of embryo development (1 to 7; where 1 = unfertilized oocyte and 7 = expanded blastocyst) and quality (1 = excellent to good and 4 = dead or degenerate) according to the IETS guidelines. The effects of follicle size (d0), P4 (d7), functional CL volume (d7), and embryo age (time from GnRH2 until embryo grading) on embryo stage and quality were analyzed using a multiple regression model. The size of the pre-ovulatory follicle in both donors and recipients was positively correlated with the functional CL volume and P4 (r = 0.45 and 0.29, respectively; P < 0.001). Functional CL volume was positively correlated with P4 (r = 0.36; P < 0.001) in donors and recipients. There were 37 oocytes and 319 embryos recovered, of which 13, 36, 189, and 81 of the embryos were stage 2, 3, 4, and ≥ 5, respectively. The majority of the embryos recovered were quality grade 1, followed by 2, 3, and 4 (196, 75, 29, and 19, respectively). As the age of the embryo increased so did the stage of development (P = 0.02) but follicle size, functional CL volume, and P4 did not affect embryo stage (P = 0.32, 0.20, and 0.44, respectively). There was a tendency for better quality embryos recovered from cows with larger follicles (P = 0.09) but functional CL volume, P4, and embryo age did not affect quality grade (P = 0.90, 0.53, and 0.30, respectively). When only transferrable embryos were included in the analysis (excluding dead [grade 4] embryos), embryo stage increased as follicle size, functional CL volume, and embryo age increased (P < 0.01) and embryo quality improved as follicle size increased (P = 0.05). In summary, follicle size at day of AI was positively correlated with P4 and functional CL volume 7 d after AI. When all embryos were analyzed, neither follicle size, functional CL volume, nor P4 affected embryo development but an increase in follicle size tended to improve embryo quality. When only live embryos were analyzed, as follicle size and CL volume increased so did the developmental stage of the embryo and quality increased as follicle size increased. PARTICIPANTS: Not relevant to this project. TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
A long term objective of this project is to determine the effect of the physiological status of an ovulatory follicle on the establishment and maintenance of pregnancy in beef cows. In the present study we found that ovulatory follicle size was positively correlated with luteal volume and serum concentrations of progesterone seven days after insemination. Although, ovulatory follicle size did not affect stage of embryo development on day seven after insemination, serum concentrations of progesterone were increased in cows that ovulated large compared to small dominant follicles. Future studies will investigate the effect of serum concentrations of progesterone on the establishment and maintenance of pregnancy following reciprocal embryo transfer of donor and receipent cows that ovulate small or large ovulatory follicles.
Publications
- Atkins, JA, Smith, MF, MacNiel, MD, and Geary, TW. 2009 Determinants of embryo development and quality in beef cattle: Effect of pre-ovulatory follicle size, CL volume, and serum concentrations of progesterone. Biol Reprod 81:505
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Progress 09/01/08 to 08/31/09
Outputs
OUTPUTS: Mechanism(s) associated with decreased pregnancy rate and increased late embryonic/fetal mortality following GnRH-induced ovulation of small dominant follicles in beef cows may be associated with decreased developmental capacity of the oocyte and(or) an inadequate uterine environment resulting from decreased preovulatory concentrations of estradiol and(or) decreased luteal progesterone secretion or stimulation. As an initial step toward elucidating the preceding mechanism(s), we are seeking to determine the effect of follicle size on embryo quality/competence and uterine environment on the establishment of pregnancy and late embryonic/fetal mortality following GnRH-induced ovulation of small (< 12 mm) or large (greater or equal to 13 mm) dominant follicles. We are currently working on the following specific aim: To determine the effect of ovulatory follicle diameter on establishment and maintenance of pregnancy following reciprocal embryo transfer to differentiate between maternal and oocyte effects on fertility. To date, 294 embryos have been transferred from and to cows at USDA-ARS, Fort Keogh on day 7 following GnRH-induced ovulation of a single small (< 12 mm) or large (greater or equal to 13 mm) dominant follicle that have not initiated standing estrous behavior. Embryos were transferred from donors to recipients based on the following GnRH-induced ovulatory follicle treatment groups: 1) small to small (n = 38 transfers; negative control), 2) large to large (n = 40 transfers; positive control), 3) small to large (n = 100 transfers), or 4) large to small (n = 116 transfers.). We anticipate completing this specific aim (66 additional transfers) and reporting the results in year 3. We hypothesized that luteal size and function are dependent on the size of the dominant follicle induced to ovulate with GnRH. Furthermore, cows with higher serum concentrations of progesterone seven days post GnRH and fixed time artificial insemenination (TAI) will have embryos that are further developed and of better quality than cows with reduced serum concentrations of progesterone. Lactating postpartum beef cows (n=315) of mixed breeds were synchronized with the CO-Synch protocol (GnRH followed 7d later with PGF2α and GnRH with TAI 48 h after PGF2α). Transrectal ultrasonography was used to measure ovulatory follicle diameter the day of TAI and CL diameter 7 d after TAI. Radioimmunoassay was conducted on serum harvested 7 d after TAI to determine concentrations of progesterone. Embryos recovered 7 d after TAI were graded for development (1 to 7 with 1 = UFO, 2 = 2-12 cell, 3 = early morula, 4 = morula, 5 = early blastocyst, 6 = blastocyst, and 7 = expanded blastocyst) and quality (1 through 4 with 1 = excellent, 2 = fair, 3 = poor, and 4 = degenerate or dying) according to the IETS guidelines. Ovulatory follicle diameter was positively correlated with both CL diameter (r = .47; P < .001) and serum concentrations of progesterone 7 d after TAI (r = .31; P < .001). CL size and serum concentrations of progesterone 7 d after TAI were positively correlated (r = .28; P < .001). PARTICIPANTS: Not relevant to this project. TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
A long term objective of this research is to determine the effect the physiological status of an ovulatory follicle on the establishment and maintenance of pregnancy in beef cows. More specifically, identification of factors affecting the development of a competent oocyte and(or) a uterine environment that is conducive to pregnancy may result in improved pregnancy rates following synchronized ovulation in beef cows.
Publications
- Atkins JA, TW Geary, and MF Smith 2008. Factors associated with ovulatory follicle growth rate and diameter in postpartum beef cows. J. Anim Sci 86:249 (abstract)
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Progress 09/01/07 to 08/31/08
Outputs
OUTPUTS: Beef cows induced to ovulate small (≤11mm) follicles had reduced establishment and maintenance of pregnancy compared to cows ovulating large (>11mm) follicles when bred after the CO-Synch protocol (GnRH1 on d-9, PGF2α on d-2, and GnRH2 with timed AI on d0). The reason for the presence of small ovulatory follicles is unknown but could be explained by failure to ovulate and synchronize a new follicular wave at GnRH1 or slower growth rate leading to GnRH2. Two experiments were conducted in cycling (n=60) and anestrous (n=55) postpartum, suckling beef cows. Cycling cows were assigned to 1 of 5 treatments (n= 12 per treatment) based on day of the cycle at GnRH1 of the CO-Synch protocol (day 2, 5, 9, 13, and 18 [estrus = d 0]). The anestrous cow experiment was a 2x2 factorial design (n=9 to 18 per treatment) based on ovulation (GnRH1+) or failure to ovulate (GnRH1-) to GnRH1 and presence (CIDR+) or absence (CIDR-) of a CIDR from GnRH1 to PGF2α. Only cows ovulating to GnRH2 were used to analyze follicle growth. Follicle growth from d-5 to 0 was greatest in day 18 cows, followed by day13, 5, 9, and 2 cows (1.1a, 0.72ab, 0.67ab, 0.66b, and 0.47b mm/d, respectively; abP<0.05). The cycling cows that ovulated following GnRH1 had faster follicle growth from d-5 to d0 than did the cows that did not ovulate (0.79 vs. 0.49 mm/d; P<0.05). Follicle growth was slower in day 2 cows than day 9 cows from d-2 to 0 (0.339 vs. 1.29 mm/d, respectively; P<0.05) but was similar among all other treatment groups (1.06, 1.13, and 1.28 mm/d in the day 5, 13, and 18 cows, respectively). In anestrous cows, GnRH1+ cows had greater follicle growth from d-5 to 0 (P<0.01) compared to GnRH1- but similar growth rate from d-2 to 0 (P>0.10), while CIDR+ cows had faster growth rate from d-2 to 0 (P<0.05) compared to CIDR- cows but the growth rate was similar from d -5 to 0. In both experiments, follicle growth was faster (P<0.05) from d-5 to d0 in cows ovulating large (>11mm) compared to small follicles. PARTICIPANTS: No Participant information reported. TARGET AUDIENCES: No Target Audiences information reported. PROJECT MODIFICATIONS: No Project Modifications information reported.
Impacts
Pregnancy rates in postpartum beef cows were decreased following gonadotropin releasing hormone (GnRH)-induced ovulation of small (≤ 11 mm) compared to large (> 11 mm) ovulatory follicles during a fixed-time artificial insemination protocol. Factors contributing to the presence of small ovulatory follicles at insemination following GnRH-induced ovulation have not been determined. Failure to synchronize a follicular wave following GnRH administration resulted in smaller ovulatory follicles at GnRH in both cycling and anestrous postpartum cows. Furthermore, the growth rate of the ovulatory follicle preceding GnRH administration was reduced for small (≤ 11 mm) compared to large (> 11 mm) follicles. Therefore, management procedures that increase follicular synchrony before GnRH-induced ovulation and insemination may reduce the proportion of small ovulatory follicles at insemination.
Publications
- No publications reported this period
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Progress 09/01/06 to 08/31/07
Outputs
Mechanism(s) associated with decreased pregnancy rate and increased late embryonic/fetal mortality following GnRH-induced ovulation of small dominant follicles in beef cows may be associated with decreased developmental capacity of the oocyte and(or) an inadequate uterine environment resulting from decreased preovulatory concentrations of estradiol and(or) decreased luteal progesterone secretion or stimulation. As an initial step toward elucidating the preceding mechanism(s), we are seeking to determine the effect of follicle size on embryo quality/competence and uterine environment on the establishment of pregnancy and late embryonic/fetal mortality following GnRH-induced ovulation of small (< 12 mm) or large (13 mm or greater) dominant follicles. We are currently working on the following specific aim: To determine the effect of ovulatory follicle diameter on establishment and maintenance of pregnancy following reciprocal embryo transfer to differentiate between
maternal and oocyte effects on fertility. To date, 100 embryos have been transferred from and to cows at USDA-ARS, Fort Keogh on day 7 following GnRH-induced ovulation of small (< 12 mm) or large (13 mm or greater) dominant follicles that have not initiated standing estrous behavior. Embryos were transferred from donors to recipients based on the following GnRH-induced ovulatory follicle treatment groups: 1) small to small (n = 13 transfers; negative control), 2) large to large (n = 15 transfers; positive control), 3) small to large (n = 23 transfers), or 4) large to small (n = 49 transfers.). Embryos recovered from these cows received an embryo morphology and quality score and embryos with quality scores 1 through 3 were transferred fresh to recipient cows. Blood samples were collected on d -19, -9, -2, 0 (second GnRH), and 7. Blood collected on d -19 and -9 will be used primarily to identify cyclic and anestrous cows. Blood on d -2, 0, and 7 will be used primarily to characterize
steroid profiles of cows as affected by ovulatory follicle size and their effects on embryo recovery, development, and pregnancy establishment. Blood collected on d 0 will also be evaluated for nutritional indicators of energy balance. To determine the effect of body temperature on embryo development and establishment rectal temperature is being collected on d -9, 0, and 7. Pregnancy was diagnosed in each recipient cow on d 28, 42, 56, and 70 in order to identify pregnancy establishment and late embryonic/early fetal mortality. So far, 75% of the embryonic losses have come from the same transfer group. Fewer embryos were transferred than anticipated in year 1, thus this specific aim may require 3 rather than 2 years to complete. Specific aims 2 or 3 will begin after completion of this experiment.
Impacts
A long term objective of this research is to determine the effect the physiological status of an ovulatory follicle on the establishment and maintenance of pregnancy in beef cows. More specifically, identification of factors affecting the development of a competent oocyte and(or) a uterine environment that is conducive to pregnancy may result in improved pregnancy rates following synchronized ovulation in beef cows.
Publications
- No publications reported this period
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