Ovarian follicular growth suppression by long-term treatment with a GnRH agonist and impact on small follicle number, oocyte yield, and in vitro embryo production in Zebu beef cows.

The aim of the present study was to evaluate small follicle number, oocyte yield, and in vitro embryo production (IVEP) in Zebu beef cows treated long term with a GnRH agonist to suppress ovarian follicular growth. Nelore (Bos indicus) cows (n = 20) showing regular estrous cycles were randomly assigned to one of two groups: control (n = 10, placebo ear implant without a GnRH agonist); GnRH agonist (n = 10, GnRH agonist ear implant containing 9.4-mg deslorelin). All cows underwent an ovum pick-up (OPU) session 14 days (Day 14) before the start of treatments (Day 0) followed by seven OPU-IVEP procedures at 30-day intervals (Days 0, 30, 60, 90, 120, 150, and 180). Semen from a single batch of a previously tested bull was used for all the IVEP. Cows treated with agonist reported a decrease over time in the proportion of animals with a (CL; P ≤ 0.05) and large follicles (>10 mm, P ≤ 0.05). These cows had a lesser number of medium + large follicles (>5 mm; 1.74 ± 0.5 vs. 4.13 ± 0.5; P ≤ 0.05), greater number of small follicles (2-5 mm; 44.3 ± 2.8 vs. 30.8 ± 1.8; P ≤ 0.05), greater yield of cumulus-oocyte complexes (COCs; 21.0 ± 2.3 vs. 15.6 ± 1.9; P ≤ 0.05), greater proportion of COCs cultured (79.2 vs. 73.9%; P ≤ 0.05), COCs cleaved (10.6 ± 1.5 vs. 6.8 ± 1.1, P ≤ 0.05), and cleaved rate (52.8 vs. 44.3%; P ≤ 0.05) compared with control cows. The number (3.4 ± 0.7 vs. 3.0 ± 0.6; P > 0.05) and proportion (16.5 vs. 19.1%; P > 0.05) of blastocysts produced were similar between agonist and control cows, respectively. The study has shown that Zebu beef cows treated long term with a GnRH agonist had follicular growth restricted to small follicles. This did not compromise the ability of oocytes to undergo IVF and embryonic development.

Improved embryonic cryosurvival observed after in vitro supplementation with conjugated linoleic acid is related to changes in the membrane lipid profile.

The aim of this study was to evaluate the effect of supplementing serum-containing media with a mixture of cis- and trans-9,11- and -10,12-conjugated isomers of linoleic acid (CLA) during different steps of the in vitro production (IVM, IVC, or IVM + IVC) of bovine embryos on their embryonic development, cryotolerance, and lipid profile. To evaluate the impact of the CLA on membrane lipids, such as phosphatidylcholine (PC) and sphingomyelin (SM), the embryos' lipid profiles were obtained using matrix-assisted laser desorption ionization mass spectrometry. The cleavage rates (78.6%-84.8%) and blastocyst development (44.8%-51.2%) remained unaltered. The postthawing reexpansion rates were higher (P < 0.05) when the CLA was added to the IVM medium (82.6%) or to the IVM + IVC medium (83.8%) than the control (69.3%) or IVC medium (63.0%). Changes in the blastocysts' lipid profile occurred when supplementation was restricted to the IVM or IVC medium. However, the most prominent effects of the CLA on the embryonic PC and SM profiles were observed when the supplement was added to IVM + IVC media, which was an increase in the level of highly unsaturated PCs containing 36 or 38 carbons, which are likely to contain CLA residues. These results showed that the molecular mechanism resulting in the improved cryosurvival, observed with CLA supplementation during bovine embryonic in vitro production, was related to the composition of structural lipids of cellular membranes and is dependent on the treatment length. Monitoring the lipid profile of embryonic membranes may improve the CLA supplementation strategy and facilitate the development of new IVC systems to improve the cryopreservation of bovine embryos and those of other domestic species.

Single nucleotide polymorphisms in the bovine genome are associated with the number of oocytes collected during ovum pick up.

The number of follicles recruited in each estrous cycle has gained practical importance in artificial reproductive technology, as it determines the oocyte yield from ultrasound-guided ovum pickup for in vitro embryo production. We aimed to identify single nucleotide polymorphisms (SNPs) in bovine genes related to reproductive physiology and evaluate the association between the candidate SNPs and the number of oocytes collected from ultrasound-guided ovum pickup. We sequenced genomic segments of GDF9, FGF8, FGF10 and BMPR2 and identified seventeen SNPs in the Bos taurus and Bos indicus breeds. Two SNPs cause amino acid changes in the proteins GDF9 and FGF8. Three SNPs in GDF9, FGF8 and BMPR2 were genotyped in 217 Nelore cows (B. indicus), while two previously identified mutations in LHCGR and mitochondrial DNA (mtDNA) were genotyped in the same group. The polymorphisms in GDF9, FGF8, BMRP2 and LHCGR were significantly associated (P<0.01) with the number of oocytes collected by ovum pickup, whereas the SNP in the mtDNA was not. In addition, we estimated an allelic substitution effect of 1.13±0.01 (P<0.01) oocytes for the SNP in the FGF8 gene. The results we report herein provide further evidence to support the hypothesis that genetic variability is an important component of the number of antral follicles in the bovine ovary.