RAPID COMMUNICATION: Residual feed intake in beef cattle is associated with differences in protein turnover and nutrient transporters in ruminal epithelium
ملخص البحث
Residual feed intake (RFI) is a widely
used measure of feed efficiency in cattle. Although
the precise biologic mechanisms associated with
improved feed efficiency are not well-known,
most-efficient steers (i.e., with low RFI coefficient)
downregulate abundance of proteins controlling
protein degradation in skeletal muscle. Whether
cellular mechanisms controlling protein turnover
in ruminal tissue differ by RFI classification is unknown.
The aim was to investigate associations between
RFI and signaling through the mechanistic
target of rapamycin (MTOR) and ubiquitin-proteasome
pathways in ruminal epithelium. One
hundred and forty-nine Red Angus cattle were
allocated to 3 contemporary groups according to
sex and herd origin. Animals were offered a finishing
diet for 70 d to calculate the RFI coefficient
for each. Within each group, the 2 most-efficient
(n = 6) and least-efficient animals (n = 6) were
selected. Compared with least-efficient
animals,
the most-efficient animals consumed less feed (P <
0.05; 18.36 vs. 23.39 kg/d DMI). At day 70, plasma
samples were collected for insulin concentration
analysis. Ruminal epithelium was collected immediately
after slaughter to determine abundance
and phosphorylation status of 29 proteins associated
with MTOR, ubiquitin-proteasome, insulin
signaling, and glucose and amino acid transport.
Among the proteins involved in cellular protein
synthesis, most-efficient animals had lower (P ≤
0.05) abundance of MTOR, p-MTOR, RPS6KB1,
EIF2A, EEF2K, AKT1, and RPS6KB1, whereas
MAPK3 tended (P = 0.07) to be lower. In contrast,
abundance of p-EEF2K, p-EEF2K:EEF2K, and
p-EIF2A:EIF2A in most-efficient animals was
greater (P ≤ 0.05). Among proteins catalyzing steps
required for protein degradation, the abundance
of UBA1, NEDD4, and STUB1 was lower (P ≤
0.05) and MDM2 tended (P = 0.06) to be lower
in most-efficient cattle. Plasma insulin and ruminal
epithelium insulin signaling proteins did not
differ (P > 0.05) between RFI groups. However,
abundance of the insulin-responsive glucose transporter
SLC2A4 and the amino acid transporters
SLC1A3 and SLC1A5 also was lower (P ≤ 0.05) in
most-efficient cattle. Overall, the data indicate that
differences in signaling mechanisms controlling
protein turnover and nutrient transport in ruminal
epithelium are components of feed efficiency
in beef cattle.
الكلمات المفتاحيه
beef cattle, insulin signaling, nutrient transporters, protein turnover, residual feed intake, ruminal epithelium