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Journal of Animal Science Abstract - Breeding and Genetics Symposium: Breeding and Genetics

039 Young scholar presentation: follicle dynamics and hormonal environment in a novel high fecundity genotype in cattle.

 

This article in JAS

  1. Vol. 95 No. supplement2, p. 18-19
     
    Published: March 31, 2017


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doi:10.2527/asasmw.2017.039
  1. A. Garcia-Guerra *12,
  2. B. W. Kirkpatrick1 and
  3. M. C. Wiltbank1
  1. 1 Univeristy of Wisconsin-Madison, Madison
    2 The Ohio State University, Columbus.

Abstract

A high fecundity bovine genotype has been recently discovered. Carriers of this allele have multiple ovulations (MO), while half-sibling non-carriers have single ovulations (SO). In sheep, high fecundity genotypes have mutations in pathways involving oocyte-derived TGF-β members, BMP-15/GDF-9. Consistent with this mechanism, MO cattle exhibit 6.6-fold greater expression of SMAD6 compared to SO (P < 5 x 10−5). SMAD6 is an inhibitor of BMP-15 transduction pathways that regulate granulosa cell proliferation and differentiation. Thus, we hypothesized that MO carriers would have reduced follicle growth rate and earlier differentiation than SO. In experiment 1, a synchronized follicular wave was induced with follicle growth in a controlled progesterone (P4) environment (intravaginal P4 implant for 5d). In experiment 2, a complete interovulatory interval was evaluated. Circulating FSH, P4, and estradiol (E2) were evaluated, and size of follicles and CL were determined by ultrasound. In experiment 1, number of ovulations was greater for MO than SO (Table 039). Mean ovulatory follicle size was greater for SO than MO; however, total ovulatory follicle volume was not different. Interestingly, follicle growth rate (volume basis) was 3.2-fold greater for SO than MO cattle. Peak FSH was similar (P = 0.65) for MO and SO with declining but similar FSH during the next 2 d. However, nadir FSH (ng/ml) concentrations were greater for MO (0.25 ± 0.02) than SO (0.17 ± 0.02; P = 0.02) cattle. In experiment 2, individual CL volume on d 7 was greater for SO than MO (Table 039); however, total luteal tissue volume and circulating progesterone was not different. In experiment 3, size for attaining ovulatory capacity was evaluated by means of a challenge with 200μg of GnRH at different intervals after wave emergence. In MO cattle, 100% (34/34) of follicles ≥ 6 mm ovulated, while in SO cattle, follicles < 7.5 mm did not ovulate (0/44) but 100% (16/16) of follicles ≥ 9 mm ovulated to the GnRH challenge. Thus, MO cows have a reduced rate of follicle growth in spite of greater nadir FSH concentrations, with smaller individual follicle volume but similar total follicle volume. In addition, follicles in MO cattle attain dominance and ovulatory capacity at smaller follicle size.


Study Endpoint MO (n = 9) SO (n = 5)
Experiment 1 Ovulations 4.1 ± 0.4A 1.6 ± 0.2B
Mean ovulatory follicle (mm) 9.43 ± 0.7A 15.5 ± 0.9B
Mean ovulatory follicle (mm3) 508 ± 127A 2033 ± 321B
Total ovulatory follicle (mm3) 2100 ± 312 3153 ± 487
Follicle growth rate (mm3) 69.9 ± 18A 225 ± 25B
Experiment 2 Ovulations 4.0 ± 0.5A 1.2 ± 0.2B
Maximal P4 (ng/ml) 8.1 ± 0.7 8.7 ± 1.2
Mean CL (mm3) 1300 ± 353A 4742 ± 668B
Total luteal volume (mm3) 4337 ± 605 4742 ± 668
AB Indicates differences within row (P < 0.05).

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