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Regular Article |
a Department of Animal Health and Biomedical Sciences, University of Wisconsin, Madison, Wisconsin 53706
ABSTRACT
Follicles of wave 1 were designated F1, F2, and so forth, according to descending diameter at the expected (F1,
8.2 mm) or observed beginning of deviation (Hour 0), as indicated by a reduction in growth rate of F2. During Hours -24 to 0 (experiment 1; n = 34 waves) and Hours -16 to 0 (experiment 2; n = 21), F1 and F2 grew in parallel (no significant differences). During Hours -16 to 0, growth rate was greater (P < 0.05) for F1 (1.4 ± 0.1 mm/16 h) and F2 (1.0 ± 0.1) than for F3 (0.6 ± 0.1) and F4 (0.5 ± 0.1). During Hours 0 to 16, growth rate was greater (P < 0.05) for F1 (1.4 ± 0.2 mm/16 h) than for F2 (0.1 ± 0.1), F3 (0.1 ± 0.1), and F4 (0.1 ± 0.2). In experiment 1, zero, one, two, or three largest follicles were ablated by aspiration of contents at Hour 0 (n = 7/group). For heifers with a single dominant follicle, the dominant follicle formed from the largest retained follicle more often when it was >7.0 mm (14 of 15) than when it was <7.0 mm (0 of 10). When the retained follicles were <7.0 mm, the first follicle to reach 7.0 mm became dominant in seven of eight heifers. Mean hour of observed deviation (occurring after Hour 0 in the ablation groups) increased progressively in groups with increasing number of ablated follicles. Plasma concentrations of FSH for groups with one, two, or three ablated follicles increased to a similar extent between Hours 0 and 12. Results supported the following: 1) during the 24 h before the beginning of deviation, small follicles grew more slowly than large follicles and the largest follicles grew in parallel; 2) after ablation of large follicles, the small retained follicles did not deviate until one reached a diameter characteristic of the beginning of deviation; 3) the potential for dominance at the expected beginning of deviation was greatest for the largest follicle and decreased progressively for the smaller follicles but only when the retained follicles were >7.0 mm; and 4) the three largest subordinate follicles began to deviate simultaneously.
1 Research supported by the University of Wisconsin-Madison, Madison, WI; U.S. Department of Agriculture grant 99-35203-7669; and The Eutherian Foundation, Cross Plains, WI.
2 Correspondence: O.J. Ginther, Department of Animal Health and Biomedical Sciences, 1656 Linden Drive, University of Wisconsin-Madison, Madison, WI 53706. FAX: 608 262 7420; ojg{at}ahabs.wisc.edu
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