Recent advances in ovulation synchronization and superovulation in ...

Abstracts. II International Symposium on Animal Biology of Reproduction, Nov. 19-22, 2008, São Paulo, SP, Brazil.
Selection of the future dominant follicle occurs earlier than previously
reported for Nellore heifers
R.L. Ereno 1 , M.F. Pegorer 1 , R.A. Satrapa 2a , R.A.L. Simões 2a , C.M. Barros 2
1 Department of Animal Reproduction FMVZ, University of Sao Paulo State (UNESP); 2 Department of Pharmacology IBB-
UNESP, Botucatu-SP, Brazil.
Introduction
In the last five years the quality and definition of ultrasound image has significantly improved, allowing the
visualization of smaller follicles than that detected by equipments initially used to characterize follicular dynamics
in bovine. In the present work, due to its capacity to measure small follicles (≥1 mm diameter) Aloka 900 ultrasound
(transrectal probe 7.5-9.0 MHz, Tokyo, Japan) was used in order to provide additional information about emergence
and deviation during the first follicular wave.
Materials and Methods
Nellore heifers (Bos taurus indicus, n = 20), were submitted to the following protocol to synchronize ovulation: on
Day -10 (D-10) all heifers received a progesterone intravaginal device (1.0 g, DIB®, Syntex, Argentina), previously
used for 8 days, and 2.5 mg of estradiol benzoate (EB, i.m., Estrogin®; Farmavet, Sao Paulo, Brazil). The
intravaginal device was removed on D-3 and PGF2α was administered (150 µg d-cloprostenol, i.m., Prolise®,
ARSA S.R.L., Buenos Aires, Argentina). Twenty four hours afterwards heifers were treated with EB (1.0 mg, i.m.),
and from this moment follicular development was monitored by ultrasonography, every 12 hours, until the sixth day
after ovulation. The time of follicular deviation was determined by visual or mathematical, Segmented Linear
Regression – SLR (1) method. The results obtained by the two methods were compared by Student’s t-test.
Results and Discussion
The emergence of the first follicular wave occurred 12 hours before ovulation, and was characterized by the
presence of a cohort of follicles (average 10.2 ± 4.08 follicles per heifer). At this time diameter (mean ± SEM) of the
largest follicle was 2.7 ± 0.11 as compared to 2.2 ± 0.21 mm of the other follicles. At the time of induced ovulation,
i.e., 12 hours after wave emergence, the number of recruited follicles increased to 14.9 ± 2.96. Since there was no
difference between visual or SLR method, the data obtained using the visual method will be presented. Follicular
deviation occurred 2.3 ± 0.21 days after ovulation, and diameter of the largest (dominant) and second largest follicle
were 5.3 ± 0.21 and 4.9 ± 0.05 mm, respectively, at this time. These results about follicular deviation in Nellore
heifers are in agreement with data published previously (2). However, in the present work, identification of the
future dominant follicle even before ovulation of the previous wave, indicates that selection of the dominant follicle
occurs earlier than previously reported for zebu cattle and agrees with recent work published by (3) in Bos taurus
taurus.
References
(1) Bergfelt DR, Sego LH, Beg MA, Ginther OJ. 2003. Calculated follicle deviation using segmented regression for
modeling diameter differences in cattle. Theriogenology, 59:1811-1825; (2) Sartorelli ES, Carvalho LM, Bergfelt
RD, Ginther OJ, Barros CM. 2005Morphological characterization of follicle deviation in Nelore (Bos indicus)
heifers and cows). Theriogenology, 63:2382-2394; (3) Jaiswall RS, Singh J, Adams GP. 2004. Developmental
patterns of small antral follicles in the bovine ovary. Biol Reprod, 71:1244-1251.
Funding and a Fellowship: FAPESP
E-mail: cmbarros@ibb.unesp.br
Anim. Reprod., v.6, n.1, p.217, Jan./Mar. 2009 217