Abstract
Angus-cross steers (n = 20; 261 ± 21.5 kg BW) were used to examine how early exposure to high concentrates or high quality forages altered marbling deposition and lipid metabolism. Steers were randomly assigned to high concentrate diet (CONC) or high quality forages (FOR) at 30-d postweaning, fed for 127 d, and slaughtered. Data were analyzed using a mixed model that included fixed effect(s) of dietary treatment (CONC vs. FOR), time (for plasma levels, ultrasound measures, and postmortem aging time) and two-way interaction (when appropriate). Steers fed CONC had greater (P < 0.01) ADG and heavier (P < 0.001) body weight at 127 d. Ultrasound measures over time showed greater (P < 0.001) intramuscular fat deposition at d 98 and 126 for CONC than FOR steers. Steers fed CONC had elevated (P < 0.05) plasma glucose and insulin concentrations from d 57 to 127 compared to FOR. Early exposure to CONC increased (P < 0.01) dressing percent, HCW, LM area, 12th rib fat thickness, and marbling scores compared to FOR. Total lipid content of the LM was greater (P < 0.01) for CONC than FOR; however, moisture, protein, and ash content was lower (P < 0.01) for CONC than FOR. Concentrate fed steers had greater (P < 0.01) MUFA content and lower (P < 0.01) polyunsaturated fatty acids PUFA n-3 content than FOR. The n-6:n-3 ratio was greater (P < 0.01) for CONC due to decreased (P < 0.01) in n-3 fatty acid content with CONC. Gene expression was up-regulated (P < 0.05) for key lipogenic genes and downregulated for glucose transporter 4 in steers fed CONC vs. FOR. Early exposure to CONC diets for 127 d at 30 d postweaning stimulated marbling deposition and resulted in these carcasses grading 80% Choice when slaughtered at 13 mo of age and 248 kg HCW.
Highlights
IntroductionCianzio et al (1985) found that hyperplasia appeared complete in several fat depots from at 19 mo of age in steers fed a grower diet but not for intramuscular fat percentage (IMF) where adipocyte number continued to increase
Marbling or intramuscular fat deposition in beef is a major determinant of carcass quality and value in the United States
The objective of this study was to examine how exposure to high concentrate diets compared to high quality forages in calves at 30 d post weaning alters marbling deposition, plasma glucose and insulin levels, and lipogenic gene expression in steers fed for only 127 d
Summary
Cianzio et al (1985) found that hyperplasia appeared complete in several fat depots from at 19 mo of age in steers fed a grower diet but not for IMF where adipocyte number continued to increase. Hood and Allen (1973) reported that adipocyte hyperplasia was complete in subcutaneous and perirenal adipocytes at steers at 14 mo of age but still involved in intramuscular fat percentage (IMF) depositions. These early studies showed that marbling deposition was more related to animal age than diet. Koch et al (2018) discovered that early exposure to high concentrate diets in calves postweaning followed by forage finishing resulted in a high percent-
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