1. BrittSBZ2008 Oocyte Development in Cattle: Physiological and Genetic Aspects Jack H Britt Institute of Agriculture, University of Tennessee, Knoxville, TN USA

2. BrittSBZ2008 Overview of Presentation Part 1. Oocyte and follicular development in cattle Part 2. Repeatability and heritability of number of follicles in cattle Part 3. Environmental effects on number and quality of follicles and oocytes

3. BrittSBZ2008 Atretic Preantral Follicles Antral Follicles Part 1. Understanding Oocyte and Follicular Development in Cattle

4. BrittSBZ2008 Primordial Follicles with Oocytes Arrested in Meiosis I Preantral Follicles Primordial Follicles

5. BrittSBZ2008 Primordial Follicle in Histological Section Adapted from: Cushman, DeSouza, Hedgpeth & Britt. 1999. Biology of Reproduction 60: 349-354 Primordial Follicle (0°) Arrested development Arrested development Primary oocyte in meiosis I Primary oocyte in meiosis I Flattened epithelial layer Flattened epithelial layer 140,000 at birth 140,000 at birth 0° 2° 1°

6. BrittSBZ2008 Primordial Follicle Population is Constant from Birth to Puberty and Then Decreases Adapted from Erickson, Journal of Animal Science 25:800-808, 1966; Hereford cattle. 98% decrease from puberty to from puberty to 17 years of age Birth to Puberty Puberty to 17 Years of Age Constant from birth to puberty (within sampling error)

7. BrittSBZ2008 Atretic Preantral Follicles Primary Follicle and Oocyte Primary Follicles

8. BrittSBZ2008 Primary (Activated) Follicle in Histological Section Primary Follicle (1°) Activated development Activated development Enlarged oocyte in meiosis I Enlarged oocyte in meiosis I Cuboidal epithelial layer Cuboidal epithelial layer Two fates: Two fates: Growth >>>> atresia Growth >>>> atresia Growth >>>> ovulation Growth >>>> ovulation 0° 2° 1° Adapted from: Cushman, DeSouza, Hedgpeth & Britt. 1999. Biology of Reproduction 60: 349-354

9. BrittSBZ2008 Atretic Preantral Follicles Secondary Follicle and Active Oocyte Secondary Follicles

10. BrittSBZ2008 Growing Secondary Follicle in Histological Section Secondary Follicle (2°) Enlarged oocyte in meiosis I Enlarged oocyte in meiosis I Visible zona pellucida (ZP) Visible zona pellucida (ZP) Multiple cuboidal epithelial layer Multiple cuboidal epithelial layer Growing follicle Growing follicle 0° 2° 1° ZP Adapted from: Cushman, DeSouza, Hedgpeth & Britt. 1999. Biology of Reproduction 60: 349-354

11. BrittSBZ2008 Atretic Preantral Follicles Antral or Vesicular Follicle Antral Follicles Vesicular is same as Antral

12. BrittSBZ2008 Preovulatory Preovulatory Monitored by ultrasound Monitored by ultrasound Multiple follicles following superovulation Multiple follicles following superovulation Genetic and environmental effects Genetic and environmental effects Mature Antral or Vesicular Follicle Prior to Ovulation

13. BrittSBZ2008 Growing Pre-antral and Vesicular Follicles From Puberty to 17 Years of Age Adapted from Erickson, Journal of Animal Science 25:800-808, 1966.

14. BrittSBZ2008 Estimated Duration of Folliculogenesis and Oogenesis in the Bovine Primordial Primordial 40 days 10 days ? GraafianAntralPreantralPrimary 80 to 100 days Britt, J. H. 1992. The Bovine Practitioner Proceedings 24: 39-43

15. BrittSBZ2008 Part 2. Numbers of Follicles are Highly Repeatable and Moderately Heritable Original slide provided by J.S. Stevenson, with permission.

16. BrittSBZ2008 Heifers with More Primordial Follicles Have More Growing & Vesicular Follicles Adapted from Erickson, Journal of Animal Science 25:800-808, 1966.

17. BrittSBZ2008 One Ovary within a Cow Can Be Used To Predict the Response of the Other Ovary to Superovulation Step 1 n = ? Count Follicles Count Ovulations X Step 3 FSH + PGF Step 2 n = ? Cushman, DeSouza, Hedgpeth & Britt. 1999. Biol. Reprod. 60: 349-354

18. BrittSBZ2008 Cows with More Corpora Lutea (CL) Had More Microscopic and Macroscopic Follicles Cushman, DeSouza, Hedgpeth & Britt. 1999. Biol. Reprod. 60: 349-354 Microscopic Macroscopic

19. BrittSBZ2008 Number of Follicles Reaching Preovulatory Size is Repeatable in Holstein Heifers and Cows Used with permission: Burns et al. 2005. BOR 73: 54-62 Holstein, heifers & cows (n=30)Holstein, heifers & cows (n=30) Ultrasound number of follicles per wave were:Ultrasound number of follicles per wave were: Low (≤15) Low (≤15) Intermediate (16-20) Intermediate (16-20) High (21-25) High (21-25) Very High (>25) Very High (>25) Repeatability of number of follicles per wave Repeatability of number of follicles per wave  r =.95  98 waves; 30 animals

20. BrittSBZ2008 Comparison Correlation coefficient Season: Spring, Summer, Fall.86 to.95 Waves per cycles: two or three.93 to.95 Lactation: lactating or dry.93 to.94 Ultrasound technician.86 to.95 Age: Heifers or Cows (see footnote).92 to.96 Overall.95 Repeatability of Number of Follicles ≥ 3 mm in Holstein Cattle is High Burns et al. 2005. Biol. Reprod. 73: 54-62 No. follicles in same animals: As heifers, 21.2±1 vs As cows, 16.4±1

21. BrittSBZ2008 Machado et al. Theriogenology 2005. 9 pair of twins, OPU at 3-4 d intervals, 195 OPU sessions (10 or 11 per donor) Only this pair differed Monozygotic Twins Produce Similar Number of Follicles and Oocytes Over Multiple Cycles

22. BrittSBZ2008 De Roover et al. 2005. Theriogenology 63: 1902. 112 cows, 665 gonadotropin-stimulated OPU sessions Cows that Have More Follicles Produce More Oocytes and Embryos in MOET Programs

23. BrittSBZ2008 Echternkamp et al. 2004. JAS 78:1564 Cattle Selected for Twinning Have More Macroscopic and Microscopic Follicles Heritability Heritability of ovulation rate =.35 in Twinner Cattle (Gregory et al. 1997 JAS 75:1213).35 =.35 MacroscopicMicroscopic Cushman et al. 2000 J. Anim. Sci. 78: 1564-1567.

24. BrittSBZ2008 Part 3. Some Environmental Effects on Follicle and Oocyte Quality Energy Balance Heat Stress Bovine Somatotropin Vitamin A

25. BrittSBZ2008 Environmental Factors that Affect Follicle and Oocyte Quality Secretes progesterone Secretes progesterone Regulates follicle waves Regulates follicle waves Regulates embryonic growth Regulates embryonic growth Required for pregnancy Required for pregnancy Ovulation The Follicle is converted to the Corpus Luteum at ovulation Examples of Environmental Effects Heat stress Energy balance Energy balance Vitamins Vitamins

26. BrittSBZ2008 Primordial Primordial 40 days 10 days ? Factors Steroids & Growth Factors Growth FSH & LH Growth Factors FSH Growth Factors FSH GraafianAntralPreantralPrimary Estimated Duration of Folliculogenesis and Oogenesis in the Bovine 80 to 100 days Britt, J. H. 1992. The Bovine Practitioner Proceedings 24: 39-43

27. BrittSBZ2008 Long-Term Treatment with Estradiol and bST Grows More Follicles Unilateral Ovex. Con E2 bST E2 bST 05067 Days from Onset of Treatments Cushman et al. 2001. BOR 65:851; Cushman et al. 2001. Therio 55:1533 Super- ovulate Treatment with bST and Estradiol

28. BrittSBZ2008 Treatment with Estradiol + bST Moved More Follicles from Primordial to Primary Pools Cushman et al. 2001. BOR 65:851; Cushman et al. 2001. Therio 55:1533 Control Estradiol + bST 1. Decrease in Primordial 2. Increase in Primary 63% 57% 38% 3. Increase in Tertiary

29. BrittSBZ2008 Treatment with Estradol + bST (Trial 1) or bST (Trial 2) Increased Number of CL Cushman et al. 2001. Therio 55:1533

30. BrittSBZ2008 Seasonal Differences in Progesterone in Blood and Tissue in Holsteins in Israel Effects of differences in P4  Oocyte environment  Follicle dominance  “Aged” oocyte and follicle  Embryo survival Wolfenson et al. Dom. Anim. Endocrinol. 22: 81-90, 2002. Follicle Cells in Culture Blood Concentrations

31. BrittSBZ2008 Follicle Development and Energy Balance Ovulation No. Follicles exposed to negative energy balance * * * * * * * = ovulatory follicle

32. BrittSBZ2008 Postpartum Cows Produce Fewer Morphologically Normal and Viable Preantral Follicles Figueiredo et al. Theriogenology 42: 1303-1310, 1994. Follicle Morphology & Growth Lowest Energy Balance & Poorest Follicles

33. BrittSBZ2008 Treatment with Vitamin A Increased Embryo Quality in Cattle Shaw et al., 1995. Theriogenology 44: 51-58.

34. BrittSBZ2008 Summary 1. Thousands of oocytes and follicles are present from late gestation through old age in cattle. 2. There is large variation among heifers and cows in number of oocytes and follicles. Heritability is approximately.35 3. Environmental factors such as nutrition, supplemental hormones, heat stress and vitamins can affect quality of follicles and oocytes

35. BrittSBZ2008 Thank You ! The University of Tennessee’s Cloned Jersey Heifers