Expression of Angiogenic Factor mRNA in the Jejunum of High and Low Efficiency Steers

We hypothesize that blood flow of the small intestine may affect efficiency of nutrient absorption and feed utilization in ruminant livestock. The objective of this study was to investigate jejunal expression of angiogenic factors in high and low efficiency steers. Hereford x Angus steers (year 1, n = 40; year 2, n = 45) were fed a finishing diet for 57 d in both years using the GrowSafe system. Residual feed intake (RFI) was calculated for each steer as the difference between actual and expected feed intake. At the end of the feeding period, the 20% most efficient (low RFI; n = 8/year) and 20% least efficient (high RFI; n = 8/year) steers were slaughtered, visceral organs were dissected, and jejunal mucosa was collected. Real-time RT-PCR was performed to determine jejunal expression of vascular endothelial growth factor (VEGF), VEGF receptors (FMS-like tyrosine kinase 1 [FLT1] and kinase insert domain receptor [KDR)]), endothelial nitric oxide synthase 3 (NOS3), and soluble guanylate cyclase (GUCY1B3; nitric oxide receptor). Relative gene expression values were analyzed for effects of RFI class, year, and their interaction. Jejunal expression of VEGF was greater (P = 0.002) in low efficiency than high efficiency steers. Year affected (P = 0.006) NOS3 expression, but KDR, FLT1, NOS3 and GUCY1B3 were unaffected (P ≥ 0.14) by RFI class, year, or their interaction. Data suggest that VEGF, a major regulator of angiogenesis, may play a role in whole animal feed efficiency, although the mechanisms remain unclear.