Effect of early grain feeding of beef steers on postabsorptive metabolism1

Abstract

The objective of this study was to determine the effect of early weaning followed by a period of high-grain feeding on plasma acetate kinetics and signaling protein phosphorylation in LM tissue of growing steers. We hypothesized that early grain feeding would result in altered cell signaling and acetate use to support observed improvements in carcass gain and marbling. Fall-born Angus × Simmental steers were weaned at 106 ± 4 d of age (early weaned [EW]; n = 6) and fed a high-grain diet for 148 d or remained with their dams (normal weaned [NW]; n = 6) on pasture until weaning at 251 ± 5 d of age. Both treatments were subsequently combined and grazed on mixed summer pasture to 394 ± 5 d of age followed by a feedlot ration until harvest at 513 ± 5 d of age. Longissimus muscle tissue biopsies were collected at 253 ± 5 and 394 ± 5 d of age and at harvest. Total and phosphorylated forms of 5' adenosine monophosphate-activated protein kinase (AMPK) and downstream proteins of the mammalian target of rapamycin signaling pathway were determined by western blotting. Eight steers were used to assess acetate clearance at different age points via a bolus infusion of acetate (4 mmol/kg of BW). Early weaned steers had greater (P < 0.05) ADG than NW steers during the early grain feeding period. Phosphorylated to total ratios of ribosomal protein S6 (rpS6) and ribosomal protein S6 kinase 1 (S6K1) were significantly different during the early grain feeding period. Phosphorylated to total ratios of S6K1, rpS6, acetyl-CoA carboxylase, and 4E binding protein 1 and the absolute amount of phosphorylated AMPK were correlated with ADG, explaining 46% of the variance. Acetate clearance rates were less (P < 0.05) and synthesis rates were greater (P = 0.06) in EW steers during early grain feeding. Acetate synthesis rates were also greater (P < 0.05) in NW steers at harvest, suggesting a permanent shift in the gut microflora or gut function in response to the treatment. Neither treatment nor acetate infusion significantly affected plasma glucose or insulin concentrations. Plasma β-hydroxybutyric acid concentrations increased with acetate infusion (P < 0.05). Based on these results, altered cell signaling during the early grain feeding period likely mediated increased protein deposition, leading to increased carcass weights, but observed changes in acetate appearance and clearance rates do not appear to explain the observed differences in intramuscular fat deposition during the terminal feeding period.

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

“…Our somewhat greater glucose turnover rates might reflect the expectation of greater glucose turnover in ruminants fed grain-based diets than those fed forage-based diets. The observed numerical differences in acetate turnover rates (P = 0.26) between the treatment groups were consistent with the significant reduction in acetate appearance rates for EW steers observed when conducting an acetate challenge test at harvest (Nayananjalie et al, 2015). Because the 2 groups were fed the same diet for at least 120 d and feed intake was not significantly different, the observed differences suggest a possible shift in gut microflora activity or changes in animal physiology contributing either to a change in tissue release of acetate or a change in gut morphology or function leading to a shift in gut microflora (see Nayananjalie et al [2015] for further discussion).…”

“…Matsuzaki et al (1997) reported plasma insulin concentrations in steers increased with increasing BW, and at 8 mo of age, they observed concentrations of 5, 2, and 3 ng/mL for Japanese Black, Japanese Brown, and Holstein breeds, respectively. Nayananjalie et al (2015) observed 0.57 ng/mL at harvest weight for steers subjected to the same treatments used herein. The in vitro studies used varied concentrations that ranged from in vivo (1 [Smith and Crouse, 1984] and 10 ng/mL [Song et al, 2001]) to much greater than in vivo (1.60 μg/mL [Lee et al, 2000]), and the observed differences in substrate preference do not seem to correlate with the deviations from in vivo.…”

“…Smith and Crouse (1984) and Song et al (2001) used 5 mM media concentrations of acetate and glucose, whereas Lee et al (2000) used 2.5 and 5 mM acetate and glucose, respectively. Plasma concentrations of glucose in steers weighing 600 kg were reported to range from 3.5 to 5 mM (Matsuzaki et al, 1997) and plasma acetate concentrations of 1.9 mM was observed by Nayananjalie et al (2015). Therefore, glucose concentrations in the in vitro studies were consistent, but acetate was greater for 2 of the in vitro studies.…”

Effect of grain inclusion rates in diets provided to early-weaned calves and steroidal implants utilization on growth performance and carcass characteristics of beef steers

“…Our hypothesis that including starch at greater rates during the early weaning phase was going to improve the MS of steers was not confirmed. Results from this experiment disagree with those that reported improvements in MS as a result of feeding starch-based diets to early-weaned calves ( Meyer et al, 2005 ; Moisá et al, 2014 ; Nayananjalie et al, 2015b ). Compared to these last experiments, the lesser ADG of steers observed in the present study during the early weaning phase, due to the limited amounts of feed offered daily, might partially explain such discrepancies.…”

“…Earlier studies reported no benefit of early grain feeding to beef calves in marbling deposition ( Myers et al, 1999 ; Fluharty et al, 2000 ; Schoonmaker et al, 2003 ). However, recent findings showed that early-weaned calves fed diets with 35% to 41% of cracked corn had a greater marbling score ( MS ) compared to their normal weaned contemporaries harvested at a common 12th rib fat thickness ( Nayananjalie et al, 2015b ). Early grain feeding to beef calves induced a precocious activation of the peroxisome proliferator-activated receptor gamma and its target genes in the Longissimus muscle ( LM ) leading to a greater IMF deposition than normal weaned calves ( Moisá et al, 2014 ).…”