RESUMO
The number of antral follicles is considered an important fertility trait because animals with a high follicle count (HFC) produce more oocytes and embryos per cycle. Identification of these animals by genetic markers such as single nucleotide polymorphisms (SNPs) can accelerate selection of future generations. The aim of this study was to perform a genome wide association study (GWAS) on Nelore and Angus heifers with HFC and low (LFC) antral follicle counts. The groups HFC and LFC for genotyping were formed based on the average of total follicles (≥ 3 mm) counted in each breed consistently ± standard deviation. A total of 72 Nelore heifers (32 HFC and 40 LFC) and 48 Angus heifers (21 HFC and 27 LFC) were selected and the DNA was extracted from blood and hair bulb. Genotyping was done using the Illumina Bovine HD 770K BeadChip. The GWAS analysis showed 181 and 201 SNPs with genotype/phenotype association (P ≤ 0.01) in Nelore and Angus heifers, respectively. Functional enrichment analysis was performed on candidate genes that were associated with SNPs. A total of 97 genes were associated to the 181 SNPs in the Nelore heifers and the functional analysis identified genes (ROBO1 and SLIT3) in the ROBO-SLIT pathway that can be involved in the control of germ cell migration in the ovary as it is involved in lutheal cell migration and fetal ovary development. In the Angus heifers, 57 genes were associated with the 201 SNPs, highlighting Fribilin 1 (FBN1) gene, involved in regulation of growth factors directly involved in follicle activation and development. In summary, GWAS for Nelore and Angus heifers showed SNPs associated with higher follicle count phenotype. Furthermore, these findings offer valuable insights for the further investigation of potential mechanism involved in follicle formation and development, important for breeding programs for both breeds.
RESUMO
ABSTRACT: The equine chorionic gonadotropin (eCG) is a glycoprotein produced in mare endometrial calices. In bovine, it is used in estrus synchronization protocols. However, studies have shown that it is potentially immunogenic and its effect can decrease after repetitive use. This study aimed to evaluate antral follicle dynamics, corpus luteum (CL) and ovulation rate in bos indicus cows submitted to an estrus synchronization protocol in association with eCG for eight times consecutively. Ten cyclical, multiparous, and pasture raised beef cows were divided into two groups: control group (n=5) and eCG group (n=5). In 30 day interval, all animals were synchronized with the same estrogen/progesterone based protocol, totalizing 8 re-synchronizations. Cows in the treatment group received 300IU eCG 48 hours prior to the presumable ovulation. Ultrassound examinations were performed on Day 4 of the protocol (approximately 1.5 days after follicle recruitment) to count antral follicles, on Day 10, to count antral follicles and to measure size of the largest follicle and on Day 18 to measure the diameter of the CL. No difference (P>0.05) between follicular growth and size of the pre-ovulatory follicle was reported between groups. Cows treated with eCG had a larger (P<0.05) CL and increased (P<0.05) ovulation rate (18mm and 92%, respectively) when compared with control group (14.1mm and 80%, respectively). Furthermore, consecutive treatments did not affect CL nor ovulation rates. In conclusion, eCG treatment increased CL size and ovulation rate even after 8 consecutive treatments.
RESUMO: A gonadotrofina coriónica equina (ECG) é uma glicoproteína produzida nos cálices endometriais da égua. Em bovinos, é utilizada em protocolos de sincronização do estro. Estudos têm mostrado que ela é potencialmente imunogênica e seu efeito pode diminuir depois de utilização repetida. O objetivo do presente trabalho foi avaliar a dinâmica folicular, o diâmetro do corpo lúteo (CL) e taxa de ovulação em vacas bos indicus submetidas a um protocolo de sincronização estral com eCG por oito vezes. Dez vacas de corte, cíclicas, multíparas e solteiras foram divididas em dois grupos: grupo controle (n=5) e grupo eCG (n=5). Em um intervalo de 30 dias, os animais foram sincronizados com um protocolo de estrógeno/progesterona, totalizando 8 re-sincronizações. Os animais do grupo tratamento receberam 300UI eCG 48 horas antes da provável ovulação. Exames ultrasonográficos foram realizados no dia 4 do protocolo (aproximadamente 1,5 dias após o recrutamento folícular), para contar folículos antrais, no dia 10, contar folículos antrais e medir o tamanho do maior folículo e, no dia 18, para medir o diâmetro do CL. Não foi encontrada diferença (P>0,05) entre folículos no dia 4 ou 10. Vacas tratadas com eCG tinham um maior (P<0.05) CL e elevada (P<0.05) taxa de ovulação (18mm e 92%, respectivamente) quando comparadas ao grupo controle (14,1mm e 80%, respectivamente). Além disso, tratamentos consecutivos não afetaram o CL nem as taxas de ovulação. Em conclusão, o tratamento com eCG aumentou o tamanho do CL e taxa de ovulação, mesmo depois de 8 tratamentos consecutivos.