Acetate and glucose incorporation into subcutaneous, intramuscular, and visceral fat of finishing steers1

Abstract

The objectives of this study were to assess the effects of early grain feeding on acetate and glucose turnover rates and acetate and glucose preference for palmitate synthesis by subcutaneous fat (SCF), intramuscular fat (IMF), and visceral fat (VF) in finishing steers. Sixteen Angus × Simmental steers were used in the study; 8 were early weaned (EW) and fed a high-grain diet immediately after weaning for 100 or 148 d, and 8 remained with their dams on pasture until weaning at 202 ± 5 or 253 ± 5 d of age. Normal weaned (NW) and EW animals were combined and grazed to 374 ± 5 or 393 ± 5 d of age, when they were placed on a corn silage-based finishing ration until they achieved a SCF thickness of 1.0 to 1.2 cm (494 ± 17 d of age for EW steers and 502 ± 12 d of age for NW steers). Immediately before harvest, steers were continuously infused for 12 h with [2H3] acetate (1.63 mmol/min; n = 8) or [U-13C6] glucose (0.07 mmol/min; n = 8). Blood samples were collected before initiation of infusions and at the end of the infusion from 8 animals or at 1-h intervals for the first 11 h and at 15-min intervals for the last hour of infusion for the other 8 animals. Adipose tissue samples from SCF, IMF, and VF depots were collected at harvest, and lipids were extracted. Plasma enrichments of acetate and glucose and palmitate enrichment in each depot were used to calculate plasma turnover rates and fractional synthesis rates (FSR; % per h) of palmitate from each isotope. Early weaned steers had greater marbling scores compared to NW steers ( P< 0.05). Plasma turnover rates and FSR for EW and NW steers were similar except for SCF, where a greater FSR from acetate was observed for EW steers. It is possible the greater FSR for SCF was due to harvesting the animals at a slightly more advanced stage of conditioning as evidenced by the trend for greater 12th rib fat (P = 0.07). Plasma acetate turnover and palmitate FSR from acetate were much greater (P < 0.05) than the corresponding rates from glucose, supporting the primary role of acetate as an energy source and the primary substrate for lipid synthesis across fat depots. However, FSR from acetate and glucose were not different among depots, suggesting that any potential effects of dietary starch on differential deposition of energy in SCF and IMF are not substrate driven.

Postweaning substitution of grazed forage with a high-energy concentrate has variable long-term effects on subcutaneous fat and marbling in Bos taurus genotypes1

“…However, the overall lack of effect of substituting high-energy supplement for pasture on IMF content during the immediate postweaning period indicates that it did not enhance development and accumulation of intramuscular adipocytes. As in later stages of growth and development, and consistent with the findings of Meteer et al (2013) and Nayananjalie et al (2015), it is likely that total energy supply is more important for adipocyte development and/or adipogenesis within IMF during the immediate postweaning phase than are substrate-specific effects.…”

Review: Nutrigenomics of marbling and fatty acid profile in ruminant meat

“…As mentioned before, early studies demonstrated that acetate and glucose are the major precursors used for biosynthesis of fatty acids in ruminants, where intramuscular adipocytes prefer glucose, and subcutaneous adipocytes prefer acetate as lipogenic substrates (Smith andCrouse, 1984, May et al, 1995). On the other hand, Nayananjalie et al (2015) detected that acetate is the main precursor for lipid synthesis across fat depots. In addition, according to Choi et al (2014), as cattle become heavier, the contribution of glucose to fat synthesis decreases whereas the use of acetate for fat synthesis increases in intramuscular adipose tissue (Figure 3).…”

Transcriptome profiling of the rumen epithelium of beef cattle differing in residual feed intake

“…It is the main site of microbial feed digestion and fermentation that produces short-chain fatty acids (SCFAs), which are a major energy source for cattle accounting for up to 80 % of total energy requirements [ 14 , 15 ]. SCFAs are mainly absorbed from the rumen [ 16 ] and metabolized within the rumen epithelium, liver and peripheral tissues to generate energy for use in maintenance, growth and activity [ 17 , 18 ]. Studies have indicated that SCFAs are absorbed by both simple diffusion [ 16 ] and protein-mediated transport through bicarbonate - dependent and - independent mechanisms [ 19 ].…”