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Location: Nutrition, Growth and Physiology

Title: Differences in antral follicle counts in pubertal Angus heifers are associated with differences in the uterine transcriptome during the late luteal phase

item McNeel, Anthony
item LARIMORE, ERIN - South Dakota State University
item AMUNDSON, OLIVIA - South Dakota State University
item Chase, Chadwick - Chad
item PERRY, GEORGE - South Dakota State University
item Cushman, Robert - Bob

Submitted to: Society for the Study of Reproduction Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 3/20/2015
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Heifers with high numbers of antral follicles conceive earlier in the breeding season, have greater follicular fluid hormone concentrations and greater uterine protein secretion. Therefore, we hypothesized that increased numbers of antral follicles associate with differentially expressed genes in the endometrium that contribute to improved fertility. Angus heifers (n=104) were submitted for ultrasonographic examination in March and April to determine antral follicle count (AFC) and endometrial diameter in order to select the heifers with the highest (n=10; High_AFC) and lowest (n=10; Low_AFC) follicle counts. Estrous cycles were synchronized with two intramuscular injections of prostaglandin F2a administered 11 d apart. Sixteen days after observed estrus, reproductive tracts were harvested, the endometrium was dissected and frozen. Total cellular RNA was extracted and individual cDNA libraries were prepared and indexed prior to sequencing on an Illumina Hi-seq 2500. Reads were aligned to the Btau UMD 3.1 and statistical analysis performed using the Tuxedo suite. Pathway analysis was conducted on differentially expressed genes. Detection of cDNA polymorphisms and associations with AFC were performed using SAMtools. Effects of SNP were predicted using SnpEFF. Differences were considered significant when the P or Q (FDR corrected P-value) was less than 0.05. High_AFC heifers had greater follicle counts (March: 27.3±1.2 vs 14.4±1.2; April: 31.3±1.9 vs 14.5±1.9; P<0.0001) and greater endometrial diameters (March: 9.4 vs 7.6 mm; April: 11 vs 9.7 mm, P<0.009) than Low_AFC heifers. There were 315 genes that were differentially expressed (Q=0.05). The top upstream regulators of gene expression included estrogen receptor and miR-1. Differentially expressed genes regulated by estrogen were C3, CALD1, FGFR1, FLNC, IGFBP5, HSP90AA1, LTF and RGS2 (Q<0.05). There was no difference in mRNA abundance of ESR1 or ESR2 (Q>0.6) between groups; however, there was a non-synonymous SNP in ESR2 that was predicted to result in a Ser > Gly substitution in the hormone binding domain of the receptor and was associated with Low_AFC (P=0.038). Functionality of the mutation is unknown. Differences in estrogen signaling during the follicular phase may alter the epigenome of the endometrium to improve uterine function during the late luteal phase resulting in earlier conception during the breeding season. Duration of estrogen exposure improved expression of estrus and expression of estrus prior to timed artificial insemination improved pregnancy rates. Future efforts aimed at improving calving day in beef heifers should focus on increasing estrogen signaling during the follicular phase through selection of replacement heifers with high antral follicle counts, genomic selection for duration of estrus, reducing clearance of estrogen through improved nutrition, or allowing estrus expression before breeding.