Body condition score at calving alters the hepatic transcriptome in grazing dairy cattle
The objective of this study was to use transcriptomics and bioinformatics to evaluate changes in hepatic gene expression profiles in cows managed to achieve a high (H, 5.5 BCS), medium (M, 4.5 BCS), or low (L, 3.5 BCS) BCS (10-point scale). Target BCS at calving were achieved by managing feed allowance before dry off. Post-calving cows were allocated pasture and pasture silage. Liver from 10 cows per BCS group was biopsied on wk 1, 3, and 5 relative to parturition. A whole-transcriptome bovine microarray (Agilent) was used. An ANOVA with repeated measures using PROC MIXED resulted in 5,888 DEG due to the main effect of BCS and 327 differentially expressed genes (DEG; False Discovery Rate <0.05) due to BCS × wk. Bioinformatics analysis was performed with the Dynamic Impact Approach (DIA), focusing on pathways from the KEGG database. The BCS × wk DEG, analysis of most-impacted pathways revealed marked differences on wk 1 for H vs. L and M vs. L; ‘fatty acid biosynthesis’, ‘biosynthesis of unsaturated fatty acids’, ‘ascorbate and aldarate metabolism’, and ‘steroid biosynthesis were among the top 5 highly-impacted pathways when comparing H vs. L and L vs. M. All were highly-inhibited in H vs. L, but highly-activated in L vs. M. The degree of impact on pathways was quite low when comparing H vs. M on wk 1 and there were few differences in pathway flux (i.e. little change in activation/inhibition). Remarkably, on wk 3, pathways in L vs. M remained activated but signaling pathways such as NOD-like receptor, p53 signaling, and RIG-I-like receptor were among the most-impacted. The most-impacted pathways in H vs. L on wk 3 were, for the most part, the same as those observed on wk 1. ‘Fatty acid biosynthesis’ on wk 3 was the most-impacted pathway and markedly inhibited in H vs. M. Data from wk 5 indicate a lesser effect of BCS at calving on the transcriptome because impact values, regardless of BCS, were substantially lower than those in wk 1 and 3. However, it is noteworthy that the ‘sulfur relay system’ pathway, key for post-transcriptional RNA modifications in mammals, was the most impacted and inhibited pathway in H vs. M. Preliminary bioinformatics analyses underscored the role of BCS at calving on liver function through alterations of the molecular phenotype and indicate a likely optimum BCS between 4.5 and 5.5.
Keywords: bioinformatics, nutrition, lactation