Investigating the ability of traditional and molecular methods to differentiate between reproductive potentials in Bos taurus heifers
Type of DegreeMaster's Thesis
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Within the livestock industry, one of the main problems that a producer faces is infertility. Infertility in cattle can lead to an animal being removed from cow-calf operations earlier in their lifetime. Reproductive technologies have helped to improve the efficiency of cattle production, however, limitations still remain. Characteristics such as phenotype and genetic background are what producers normally base their decisions off of when deciding on replacement heifers. Currently, there is a lack of informative biomarkers that would help to identify replacement heifers. The levels of the metabolites present within the blood plasma can be compared between heifers of different phenotypes and could provide a basis to discriminate heifers based on their reproductive potentials. The objective of this study was to identify differences in metabolomic profiles between heifers at the time of weaning based on their pregnancy outcomes. Angus/Simmental-cross heifers (n=36) housed at the Black Belt Research and Extension Center were assessed at weaning and 10 ml of blood was collected. The blood plasma and white blood cells (WBCs) were isolated. Heifers were then assessed 30 days prior to artificial insemination (AI) for weight, pelvic area (PA), body condition scores (BCS) and reproductive tract scores (RTS). Reproductively mature heifers underwent a fixed-time AI program with estrus detection and were then exposed to a bull two weeks after AI. Pregnancy was determined via rectal palpation and heifers were categorized into three groups: pregnant by AI, pregnant by natural breeding or open after AI and 60 days of bull exposure. 9 heifers pregnant by AI and 11 open were chosen for metabolomic profiling. Of the 20 heifers selected, there was no difference in age at weaning, weaning weight, BCS, RTS or pelvic area (p > 0.05). Ten metabolites were found to be significantly up or down regulated in the heifers who remained open after AI and 60 days of bull exposure, when compared to those pregnant by AI. Alanine, cystine, lysine, methionine, tyrosine, tryptophan and valine were down regulated. Glycerol, frustose-6-phosphate and ribulose- 5-phosphate were found to be upregulated in open heifers (p<0.05). RNA isolated from white blood cells was used to determine the expression of five inflammatory cytokines in the open and pregnant by AI groups (TNFα, IL6, CXCL5, POSTN and MCP1). Inflammatory cytokines were increased in all heifers that remained open after AI and 60 days of bull exposure (p < 0.05). Lastly, ELISAs were used to detect proteins for TNFα and IL6. The differences between heifers pregnant by AI and open was not significant with p > 0.05. In summary, the quantity of specific metabolites present within the blood plasma are different at weaning between heifers with differing reproductive potentials. This could potentially be used to develop an assay to aid in selecting replacement females to incorporate into an existing herd.