175 FOLLICULAR DIAMETER AND OVULATION RATE IN NELLORE COWS TREATED WITH LH
R. A. L. Simões* A , F. S. Rosa** A , M. Piagentini C , R. A. Satrapa* A , R. L. Ereno C , T. Nabhan** A , L. A. Trinca B , M. F. G. Nogueira D and C. M. Barros AA Dept. of Pharmacology, IB, UNESP, Botucatu-SP, Brazil;
B Dept. of Biostatistic, IB, UNESP, Botucatu-SP, Brazil;
C Dept. of Animal Reproduction, FMVZ, UNESP, Botucatu-SP, Brazil;
D Dept. of Biological Science, UNESP, Assis-SP, Brazil
Reproduction, Fertility and Development 21(1) 186-187 https://doi.org/10.1071/RDv21n1Ab175
Published: 9 December 2008
Abstract
The aim of the present experiment was to verify the correlation between follicular diameter and ovulation rate in Nellore cows submitted to LH treatment to add information to the limited literature about this subject. A preliminary test (experiment 1) was performed to determine the lowest dose of LH necessary to induce ovulation in follicles with diameter ≥10 mm. At a random stage of the estrous cycle (D0), Nellore cows (n = 20) received a progesterone intravaginal device (1.0 g, Primer®, Tecnopec, Sao Paulo, Brazil) and 2.5 mg of estradiol benzoate (EB, i.m., Estrogin®; Farmavet, Sao Paulo, Brazil). Eight days later (D8) PGF2α was administered (150 μg of D-cloprostenol, i.m., Prolise® ARSA S.R.L., Buenos Aires, Argentina) and the device was removed. Twenty-four hours after device removal, cows were treated with EB (1.0 mg, i.m.) and 48 h afterward; ovulation was determined by ultrasonography (US, Aloka 900, Tokyo, Japan). Three days after ovulation, the follicular growth was daily observed by US, and when the follicles reached ≥10 mm diameter, the cows were randomly allocated in 4 groups and treated with different doses of LH (i.m., Lutropin-V®, Bioniche, Ontario, Canada): Groups 1.56; 3.12; 6.25, and 12.5 mg. The data were analyzed by Fisher’s Exact Test (PROC FREQ, SAS). The ovulation rates were 0% (0/5), 80% (4/5), 80% (4/5), and 80% (4/5) respectively, and it was lower in group 1.56 when compared with the others (P < 0.02). Taking in account the results above, the dose of 6.25 mg to induce ovulation in Nellore cows (n = 58, experiment 2) submitted to the same protocol used in experiment 1 and randomly allocated in 5 groups according to follicular diameter at the time of LH administration: G1 (7.0–7.5 mm), G2 (7.6–8.0 mm), G3 (8.1–8.5 mm), G4 (8.6–9.0 mm), and G5 (9.1–10.0 mm). The results were analyzed by Logistic Regression (PROC GENMOD, SAS). The ovulation rates were 0% (0/11), 20% (2/10), 36% (4/11), 36% (4/11), and 90% (9/10), respectively, for G1, G2, G3, G4, and G5. When the data from 2 groups (except G5) were combined, G1 + G2 (7.0–8.0 mm), G3 + G4 (8.1–9.0 mm), and G5 (9.1–10.0) ovulation rates were, respectively, 9% (2/21), 36% (8/22), and 90% (9/10). There were significant differences when comparing G1 + G2 v. G5 (P < 0.01), G3 + G4 v. G5 (P < 0.02) and G1 + G2 v. G3 + G4 (P < 0.03). After LH application, the smallest follicle that ovulated had a diameter of 7.65 mm. In summary, although LH administration induced ovulation in one follicle of 7.65 mm, high ovulation rates were observed only when the follicles reached <9.0 mm. These data will be used to study the correlation between ovulation rate and expression of isoforms of LH mRNA receptors in theca and granulosa cells.
Fellowship from *FAPESP (Sao Paulo, Brazil) and **CAPES (Brasilia, Brazil).
