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RESEARCH ARTICLE

14 IS THE LOW NUMBER OF OVARIAN ANTRAL FOLLICLES ≥3 mm IN DIAMETER ASSOCIATED WITH LOW FERTILITY IN LACTATING NELORE COWS?

V. G. Pinheiro A , R. L. Ereno A , E. M. Razza A B , C. M. Barros A and M. F. G. Nogueira B
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A Department of Pharmacology, IBB, São Paulo State University (UNESP), Botucatu, São Paulo, Brazil;

B Department of Biological Sciences, FCL, UNESP, Assis, São Paulo, Brazil

Reproduction, Fertility and Development 27(1) 99-100 https://doi.org/10.1071/RDv27n1Ab14
Published: 4 December 2014

Abstract

The follicular growth in cattle occurs in a wave pattern of 2 to 3 waves per oestrous cycle and is characterised by synchronous growth of a cohort of antral follicles, where usually only one of these will become dominant. The amount of recruited follicles per wave is variable between animals and breeds but is highly repeatable among individuals. Some studies report that in Bos indicus the amount of follicles recruited by wave is higher when compared with Bos taurus. The variation in the size of the ovarian follicular population can affect fertility by influencing oocyte competence (Ireland et al. 2007). We aimed to identify Nelore (Bos indicus) cows with high and low numbers of antral follicles recruited by follicular wave and to compare their pregnancy rates. We used 268 multiparous Nelore cows between 40 and 70 days postpartum and body condition score between 3.5 to 4.5 (5-point scale). The cows were sorted in ascending order according to the average number of follicles at all examinations (≥3 mm in diameter). Hence, 33% of animals with the greater follicular population were enrolled in the high population group (HG, n = 89, ≥38 follicles), whereas the intermediate animals (33%) were placed in the intermediate group (IG, n = 88, between 28 and 38 follicles), and animals (33%) with lower follicular population were included in the low population group (LG, n = 91, ≤28 follicles). The animals underwent 3 ultrasound examinations (days D–10, D0, and D28). In D0, at random day of the oestrous cycle, all cows received an intravaginal device containing progesterone (1.0 g, DIB®) and oestradiol benzoate (EB, 2.0 mg, IM, Estrogin®). Eight days later (D8) we administered 75 μg of d-cloprostenol (Croniben®), and the intravaginal device was removed. Twenty-four hours after DIB removal, the cows were treated with EB (1.0 mg, IM), and after 30 to 36 h animals were AI at a fixed time. Data were analysed using PROC GENMOD SAS System 9.1 for Windows (2002–2003). The mean (±SD) of antral follicles in both ovaries was 32.7 ± 17.8. There was no difference (P = 0.144) in pregnancy rates between the HG, LG, and IG animals (32.6, 46.6, and 42.9%, respectively). Thus, we conclude that there was no difference in pregnancy rates between Nelore cows either with high or low population of ovarian antral follicles after AI at a fixed time.

Research was supported by grants #2013/02201-3 (VGP), #2011/50259-5 (RLE), #2012/23409-9 (EMR), #2012/50533-2 (MFGN), São Paulo Research Foundation (FAPESP).


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