Expression of Nutrient Transporter mRNA in the Jejunum of High and Low Efficiency Steers
We hypothesized that small intestinal expression of nutrient transport-related genes contributes to differences in metabolic efficiency in beef cattle. The objective was to investigate jejunal expression of glucose transporter 2 (GLUT2), glucose transporter 5 (GLUT5), sodium-dependent glucose transporter 1 (SGLT1), and peptide transporter 1 (PepT1) in finishing steers classified as high and low efficiency based on residual feed intake (RFI). Hereford-Angus crossbred steers (yr 1, n = 59, 461 ± 4.5 kg initial BW; yr 2, n = 75, 412 ± 3.8 kg initial BW) from a single contemporary group in each year (birth through slaughter) were used. Steers were fed a finishing diet (yr 1, 11.4% CP, 2.0 Mcal NEm/kg, 1.35 Mcal NEg/kg; yr 2, 13.2% CP, 1.8 Mcal NEm/kg, 1.19 Mcal NEg/kg; DM basis) for 57 (yr 1) or 80 d (yr 2) using the GrowSafe system. Residual feed intake was calculated as the difference between actual and expected feed intake of each individual, where expected intake was determined by regressing ADG and metabolic midweight on actual intake. Following the intake test in each year, the 20% most efficient (low RFI, n = 8/yr) and 20% least efficient (high RFI, n = 8/yr) steers with 12th rib fat thickness ≥1.02 cm were slaughtered between 5 and 8 d after the feed intake test conclusion. At slaughter, jejunal mucosa was flash-frozen for real-time RT-PCR determination of GLUT2, GLUT5, SGLT1, and PepT1. Data were analyzed with PROC MIXED in SAS 9.2 using RFI class (high vs. low efficiency), year, and their interaction as fixed effects. Expression of SGLT1 was affected (P = 0.02) by the RFI class x year interaction, although there were no differences (P ≥ 0.12) within each year. Jejunal expression of GLUT2, GLUT5, and PepT1 were not affected (P ≥ 0.18) by RFI class; however, expression of each was greater (P ≤ 0.03) in yr 2 than yr 1. It was previously reported in this study that jejunal expression of y+LAT2, a basolateral membrane cationic AA transporter, was greater for low efficiency than high efficiency steers in yr 2. Additionally, low efficiency steers had greater jejunal expression of vascular endothelial growth factor (VEGF, a major regulator of angiogenesis) than high efficiency in both years. These data suggest that nutrient absorption and transport in the small intestine may play a role in whole animal feed efficiency of beef cattle.
feed efficiency, nutrient transport, small intestine