Exploring immunoglobulin and metabolomic biomarkers of subfertility in Bos taurus beef heifers

Abstract

Unexplained heifer subfertility is a resource drain on beef production, negatively effecting production efficiencies. Animals that do not conceive within a breeding season and those conceive late result in lighter calves and less return on investment for producers upon weaning and marketing. The ability to detect and avoid heifers that fail to become pregnant, or become pregnant late, would improve the efficiency of beef production. In biomarker discovery, highly accessible animal samples are preferable such as in blood, saliva, and urine. The objectives of this study were to identify the differences in plasma immunoglobulin levels and metabolomic signatures at different stages of heifer development. To accomplish this, the relative immunoglobulin G (IgG) levels in the blood plasma were tested using SDS-PAGE and Western blot between Bos taurus beef heifers that conceived to first service AI and those that conceived late or not at all in the breeding season (1stAI, n=12; LBred, n=12). There was no significant difference in the levels of IgG1 between heifers that established pregnancy to first-service AI and those that established pregnancy late in the breeding season. However, IgG2 levels were significantly higher in heifers that established pregnancy to first service AI. In the second study, blood plasma metabolomic profiles generated by gas chromatography-mass spectrometry (GC-MS) were compared for Bos taurus beef heifers that conceived to AI (fertile, n=6) and heifers that conceived late or not at all (subfertile, n=6) at weaning and for a subset of the same heifers 30 days prior to AI (fertile n=3, subfertile n=4). At weaning, six metabolites were present at significantly lower levels in fertile heifers compared to subfertile heifers, including arabitol, glycolic acid, indole-3-lactate, indole-3-propionic acid, and palmitoleic acid. Three metabolites were present at significantly higher levels in fertile heifers, including lactic-3-acid, maltose, and nicotinamide. Thirty days prior to AI, four metabolites were differentially abundant. In fertile heifers, tryptophan was at higher levels, and palmitoleic acid, triethanolamine, and 9-myristoleate were at lower levels. Five metabolites changed levels significantly over time within cohorts, including palmitoleic acid, 1,5-anhydroglucitol, capric acid, myristic acid, and isolinoleic acid. For the third study, metabolomic profiles were generated for blood plasma and follicular fluid from beef heifers that either conceived at AI or remained non-pregnant following fixed time artificial insemination and 60-day exposure to fertile bulls (fertile, n=8; subfertile, n=5). Fourteen differentially abundant metabolites were identified in follicular fluid, including arachidonic acid and ascorbic acid and four were identified in blood plasma, including fucose and lactic acid. Fucose and pipecolinic acid showed medium correlation between blood plasma and follicular fluid and high ROC-AUC values in blood plasma. In plasma and follicular fluid of post-breeding season animals, identified metabolites were related to reactive oxygen species, energy metabolism, and cell growth and proliferation. Correlation of plasma and follicular fluid profiles suggests that two differentially abundant metabolites in plasma may be tightly correlated enough to follicular fluid to serve as diagnostic of the follicular state; however, these statistical results need to be specifically and carefully validated with a targeted study.