mRNA Expression of Selected Candidate Genes in the Bovine Oviduct Is Influenced by the Energy Status as a Long-Term Effect.

The milk yield of dairy cows has increased in the last decades. Furthermore, an increase in the severity of the negative energy balance (NEB) of dairy cows in the first weeks of the lactation period has been noted. It is discussed that decreasing fertility rates of dairy cows are directly attributed to this finding. Aim of this study was to analyze the mRNA expression pattern of selected candidate genes in the bovine oviduct in correlation with long-term effects of energy status. 24 multiparous Holstein-Friesian cows were included in this study. Negative energy balance was calculated weekly from food intake, milk yield and body weight. Furthermore, the amount of subcutaneous body fat mobilisation (BFM) was measured weekly as thickness lost since week 1 ante partum. Therefore, three groups (n=8) were accordingly defined: highest, medium or lowest BFM or NEB, respectively. In addition, the first luteal activity was recorded. Cows were slaughtered at least 10 weeks post partum (pp). Oviducts were collected directly after slaughter and classified according to distinct estrous cycle phases or metabolic classes. Total RNA was isolated from scraped oviductal mucosal cells and subjected to real-time RT-PCR amplification. The obtained mRNA expression data were correlated with the distinct energy status as long-term effects. About 30 candidate genes were selected which are associated with local reproductive events; e.g. growth factors, extracellular matrix components and enzymes involved in the prostaglandin synthesis. Statistical analysis showed if expression pattern were influenced by the factor estrous cycle, they were unaffected by the influence of the metabolic factors and vice versa. Mainly the mRNA expression of members of growth factor families like fibroblast growth factor (FGF) or vascular endothelial growth factor (VEGF) was affected by different BFM. FGF2 showed higher expression in animals with higher BFM in weeks 2 and 3 pp, but low expression directly after ovulation. VEGFA was positively correlated in its expression pattern with NEB. Matrix metalloproteinase 2 and its inhibitor (TIMP1) as well as the insulin-like growth factor 1 were expressed higher after ovulation compared with the luteal phase, but not influenced in their expression pattern by the energy status. Cyclooxygenase 2 (PTGS2) expression was neither influenced by the estrous cycle stage nor the energy status. PTGS1 and phospholipase A2G4B oviductal mRNA expression was higher in cows which showed early luteal activity compared with the cows having a delayed first cycle. However, PTGS1 expression was higher in the oviduct of cows with low energy balance or highest back fat thickness after week 9 pp. Enzymes for metabolizing hydroxybutyrate were expressed higher after ovulation, but their expression was not affected by the energy status. Progesterone receptor mRNA was expressed significantly higher after ovulation and in cows with early luteal activity. In contrast, estradiol receptor alpha expression was only influenced by the energy status. It seems that BFM and NEB can affect mRNA expression patterns of key factors for reproductive events even weeks after their occurrence. Since these factors are an integral part of the fine-tuned cross-talk in bovine reproduction, their expression changes due to energy imbalance may help understand the causes of poor fertility often associated with NEB. Supported by BMBF (Fugato-plus REMEDY).