Association of glucose metabolism and insulin resistance with feed efficiency and production traits of finishing beef steers.

Increasing nutrient utilization efficiency is an important component of enhancing the sustainability of beef cattle production. The objective of this experiment was to determine the association of glucose metabolism and insulin resistance with dry matter intake (DMI), average daily gain (ADG), gain:feed ratio (G:F), and residual feed intake (RFI). Steers (n = 54; initial body weight = 518 ±â€…27.0 kg) were subjected to an intravenous glucose tolerance test (IVGTT) where glucose was dosed through a jugular catheter and serial blood samples were collected. Three days after the last group's IVGTT, steers began a 63-d DMI and ADG test. Body weight was measured on days 0, 1, 21, 42, 62, and 63, and DMI was measured using an Insentec Roughage Intake Control system (Hokofarm Group, Emmeloord, the Netherlands). To examine relationships between DMI, ADG, G:F, and RFI with IVGTT measurements, Pearson correlations were calculated using Proc Corr of SAS 9.4 (SAS Inst. Inc., Cary, NC). Additionally, cattle were classified based on DMI, ADG, RFI, and G:F, where the medium classification was set as mean ±â€…0.5 SD, the low classification was < 0.5 SD from the mean, and the high classification was > 0.5 SD from the mean. No associations between DMI and IVGTT parameters were observed, and no differences were detected when classifying cattle as having low, medium, or high DMI. Peak insulin concentration in response to the IVGTT tended to be correlated with ADG (r = 0.28; P = 0.07), indicating cattle with greater ADG tend to have a greater insulin release in response to glucose. Glucose nadir concentrations tended to be positively correlated with ADG (r = 0.26; P = 0.10). Additionally, the glucose nadir was greater in high-ADG steers (P = 0.003). The association of greater glucose nadir with high-ADG could indicate that high-ADG steers do not clear glucose as efficiently as low-ADG steers, potentially indicating increased insulin resistance. Further, RFI was not correlated with IVGTT measurements, but low RFI steers had a greater peak glucose concentration (P = 0.040) and tended to have a greater glucose area under the curve (P = 0.09). G:F was correlated with glucose area under the curve (r = 0.33; P = 0.050), glucose nadir (r = 0.35; P = 0.011), and insulin time to peak (r = 0.39; P = 0.010). These results indicate that glucose metabolism and insulin signaling are associated with growth and efficiency, but the molecular mechanisms that drive these effects need to be elucidated.

Feed efficiency is an important component of improving the sustainability of beef production. There is a need to understand how metabolism influences feed efficiency. This experiment aimed to explore the association of glucose metabolism and insulin resistance with feed intake, growth, and efficiency of finishing beef cattle. The results indicate that there is a relationship between insulin resistance and improved efficiency measured as the ratio of growth to feed intake. The findings of this experiment are novel as they show a relationship between insulin resistance and feed efficiency and indicate further research is needed to determine the mechanisms of insulin resistance in ruminants that contribute to improved feed efficiency.

Impact of endophyte-infected tall fescue seed consumption on endocrine changes associated with intake regulation and post-absorptive metabolism in growing steers.

Fescue toxicosis is a syndrome occurring from the consumption of endophyte-infected tall fescue and results in substantial economic losses to the beef industry primarily from reduced growth accompanied by decreased dry matter intake (DMI); however, the associations characterizing this reduction in DMI have yet to be elucidated. The objective of this experiment was to identify endocrine changes associated with intake regulation post-consumption of endophyte-infected tall fescue seed (E+). Twelve Holstein steers were stratified by body weight and assigned to 1 of 3 treatments (n=4): 0 ppm ergovaline (ERV), 1.8 ppm ERV, or 2.7 ppm ERV. Treatments were achieved by combining differing proportions of ground E+ and non-endophyte-infected tall fescue seed. Steers were adapted to their diets for 7 d followed by a 7 d DMI collection period. Within treatment, steers were assigned to a sampling day (d 16 or d 17). Blood samples were collected every 20 min for 8 h, beginning 1 h before feeding. Intake data was analyzed using the MIXED procedure of SAS 9.4 (SAS Inst. Inc., Cary, NC) with treatment, day, and the interaction as fixed effects. Hormone and metabolite data were analyzed with the fixed effect of treatment, time, and the interaction including time as a repeated measure and orthogonal contrasts. Dry matter intake was linearly decreased with increasing ERV in the diet (P < 0.001). Insulin and leptin concentrations exhibited a quadratic effect (P = 0.018 and P = 0.005) with insulin concentrations highest for the 2.7 ppm treatment and leptin concentrations highest for the 1.8 ppm treatment. No differences were detected for active ghrelin or ß-hydroxybuytrate concentrations among treatment groups. Further, steers consuming both the 1.8 and 2.7 ppm ERV treatments had lower prolactin concentrations compared to the 0 ppm treatment (quadratic, P= 0.019). Glucose concentrations had a tendency for a linear increase as ERV concentrations increased (P = 0.091). A treatment × time interaction (P = 0.002) was noted in NEFA concentrations, with the 1.8 ppm ERV treatment showing increased pre-feeding concentrations, and the 2.7 ppm ERV treatment exhibiting elevated NEFA concentrations as time post-feeding progressed. The results suggest that E+ consumption reduces intake likely through alterations in intake-related hormones and post-absorptive metabolism and contributes to our current understanding of E+ effects on intake reduction while providing avenues for future research.

Technical note: Validation of energy dispersive X-ray fluorescence for determination of indigestible markers in ruminant fecal and rumen fluid samples.

Determination of digestibility and passage rate is important for further understanding of nutrient utilization and thereby aids in improving nutrient utilization efficiency. Titanium dioxide and chromium ethylenediaminetetraacetic acid are commonly used as indigestible markers for determining passage rates of diets to aid in determination of digestibility. Analyzing Ti and Cr involves the use of procedures such as acid digestions, inductively coupled plasma spectroscopy, and atomic absorption. These commonly used methodologies involve hazardous chemicals, destruction of samples, and low sample throughput. The objective of this experiment was to develop and validate an accurate and precise method for measuring both Ti and Cr using energy dispersive X-ray fluorescence (ED-XRF). Energy dispersive X-ray fluorescence is an analytical technique used for analyzing elements in various sample types. The samples were added to the ED-XRF machine and irradiated with X-rays. The intensity of the X-rays emitted (termed fluorescent X-rays) was used for calculation of the concentration of the element. The method for Ti was constructed using fecal samples from cattle consuming three different diet types (finishing diet, dairy lactation diet, and grazing native range pasture). The Cr method was developed for rumen fluid analysis. We compared the machine-calculated concentrations of each element to the concentration calculated by a standard curve. For both the Ti and Cr, the standard curve-calculated value had a lower percent difference overall at 4.56% and 12.59%, respectively, compared to the machine percent difference of 8.35% and 16.38% for Ti and Cr, respectively. To determine accuracy and precision of the method, samples were spiked with various amounts of Ti or Cr and measured for their respective compounds with percent recovery and inter- and intra-assay CV-calculated thereafter. The average recovery for Ti across all diet types was 100.3%, and the recovery for Cr in rumen fluid was 95.7%. The average inter- and intra-assay CV for Ti, across all diet types, were 9.70% and 2.16%, respectively. For Cr, the average inter- and intra-assay CV were 5.42% and 8.45%, respectively. The ED-XRF method requires minimal additional chemicals, is cost-effective, and allows for sample preservation as well as a high throughput of samples. Our results indicate utilization of ED-XRF is an accurate and precise method for determination of Ti in feces and Cr in rumen fluid.

Markers are elements supplied to an animal to help determine the digestibility of various feedstuffs. Studying digestibility allows us to improve how nutrients are used by animals and reduce production costs and environmental impact. The method proposed here uses an X-ray fluorescence machine to analyze the markers with no hazardous chemicals, low labor input, and cost. Even though this equipment utilizes radiation, the construction of the equipment eliminates the exposure of operators to radiation. Training and monitoring will differ between institutions. Traditional methods use hazardous chemicals and have higher cost and labor use. We determined that this is a valid method for analyzing titanium in fecal samples and chromium in rumen fluid.