Effects of dietary fat and protein from corn coproducts on growth, carcass characteristics, ruminal metabolism, and genomic regulation of marbling development in early-weaned beef cattle

Four experiments were conducted to evaluate the effects of dietary fat and protein from corn coproducts on growth, carcass characteristics, ruminal metabolism, methane production, and transcriptional regulation of marbling. In Exp. 1, crossbred heifers (n = 150) and steers (n = 100) were used to evaluate 1 of 5 growing diets in a 2 × 2 + 1 factorial arrangement of treatments: 1) corn-based control; 2) low fat, low protein coproduct blend; 3) high fat, low protein coproduct blend; 4) low fat, high protein coproduct blend; 5) high fat, high protein coproduct blend. Low protein and low fat diets were formulated to be isonitrogenous with similar fat content to control (16.0% CP, 3.0% fat), and high protein and high fat diets were formulated to be 20.0% CP and 5.0% fat respectively. Calves were weaned at 90 d, blocked by sex and then by weight into 25 pens (10 hd/pen). The objective of this experiment was to determine if differing concentrations of protein and fat in coproduct-based growing diets of early-weaned calves affect feedlot performance and carcass composition. Calves were fed experimental diets for 112 d and then acclimated to a common feedlot diet for an additional 112 d. Body weight, hip height (HH), and ultrasound data were collected at the end of each 112d feeding phase. Carcass data included HCW, LM area (LMA), 12th rib back fat (BF), marbling score (MS), KPH, and USDA QG. No interactions (P ≥ 0.27) of fat and protein concentration were detected; therefore, main effects are discussed. No effects (P ≥ 0.12) of control, protein, or fat were detected for BW, or HH. Calves consuming increased dietary protein from coproducts had increased (P = 0.04) ADG in the growing phase. Feeding cattle control decreased (P = 0.04) DMI, and increased (P <0.01) G:F during the growing phase and feeding phase. Ultrasound revealed increased (P = 0.05) BF in calves fed high fat at d 112. High protein diets decreased (P = 0.02) ultrasound MS at d 112. Carcasses from cattle fed high fat diets had greater (P = 0.03) MS compared to those from cattle fed low levels of dietary fat. Carcasses from cattle fed high protein diets had reduced (P < 0.01) percentage of carcasses that graded Prime compared to carcasses from cattle fed increased concentrations of fat. No differences (P ≥ 0.15) were observed for HCW, LMA, BF, KPH, or YG. Cattle fed high protein diets produced fewer (P < 0.01) carcasses that graded Prime than cattle fed low protein diets. These data indicate that growth was unaffected by protein and fat concentration in growing calf diets, but MS and QG were positively influenced by fat and protein concentration in early calf diets. In Exp. 2, Longissimus lumborum of thirty crossbred calves (Age = 95 ± 1.7 d; BW = 179 ± 18 kg) were fed diets from experiment 1. Biopsies were collected from the LM at 0, 112, and 224 d for transcriptional analysis via RT-qPCR of 14 genes associated with adipogenesis and lipogenesis within the muscle. The objective of this experiment was to examine the effect of dietary fat and protein concentration on serum concentrations of leptin, IgF1 and growth hormone, and gene expression of fourteen genes that regulate lipid metabolism and adipogenesis. Serum was collected at d 0, 112, and 224 and analyzed for leptin, insulin-like growth factor 1, and growth hormone concentration. Data were analyzed to ascertain the effects of protein level, fat level, time, and their interactions on gene expression and blood metabolite concentration. Increased protein and decreased fat in the growing diet resulted in a protein × fat × day interaction characterized by a carryover effect which increased (P < 0.01) gene expression of PPAR gamma, insulin induced gene 1, thyroid hormone responsive SPOT14 protein, ATP citrate lyase, adiponectin, diacylglycerol O-acyltransferase homologue 2, fatty acid binding protein 4, fatty acid synthase, phosphoenolpyruvate carboxykinase 1, and stearoyl-CoA desaturase, as well as, serum leptin concentrations during the finishing phase. Expression of sterol regulatory element binding transcription factor 1 was increased (P < 0.01) at d 112 in steers fed high protein, high fat diets compared to those fed high protein, low fat diets. A fat × day interaction (P < 0.01) occurred for the expression of ADIPOR2 and CEBPA resulting in a carryover effect wherein low fat diets fed during the growing phase increased expression of both genes at the end of the finishing phase (d 224). Carcasses from cattle fed control during the growing phase tended (P = 0.09) to have higher marbling scores while other carcass parameters were not different (P ≥ 0.13). These data indicate that feeding differing levels of dietary fat and protein during the growing phase does affect intramuscular adipogenesis at the transcriptional level, but differences in gene expression were not sufficient to affect carcass quality among cattle fed coproducts. In Exp. 3, 40 steers (age = 134 ± 3 d; BW = 185 ± 11 kg) were randomly allotted to 1 of 5 dietary treatments: 1) corn-based control (CNT), 2) 0% corn distillers solubles (CDS), 3) 10% CDS, 4) 19% CDS, or 5) 27% CDS. Diets 2–5 included coproducts (corn gluten feed and soybean hulls) and were formulated to achieve fat concentrations of 3, 5, 7, and 9%, respectively. Diets were fed once daily for 106 d growing phase. All steers were fed a corn-based diet from d 107 to 196 (finishing phase). Contrasts were used to examine a) the difference between CNT and 10% CDS; b) linear and quadratic effects of CDS inclusion. The objective of this experiment was to evaluate differences in growth and carcass traits associated with feeding either starch or increasing levels of CDS. During the growing phase, steers fed CNT had increased (P ≤ 0.03) BW, G:F and ADG compared to those fed 10% CDS. Increasing CDS inclusion increased (linear; P = 0.01) ADG and G:F. At the conclusion of the growing phase, BF determined via ultrasound was greater (P = 0.05) in CNT-fed calves compared to 10% CDS. There were no treatment differences (P ≥ 0.14) in finishing phase ADG, DMI, or G:F. Steers fed CNT had increased (P = 0.02) overall ADG compared to steers fed 10% CDS, and increasing CDS inclusion increased (linear; P = 0.05) overall ADG. Final BW, and overall DMI and G:F were not different (P ≥ 0.06). There were no effects (P ≥ 0.10) of treatment on carcass traits. Feeding a coproduct diet with 10% CDS during the GP decreased overall ADG compared to feeding corn. Finally, in Exp. 4, steers (n = 5; BW = 345 ± 22 kg) were fed Exp. 3 diets for ad libitum intakes in a 5x5 Latin square design. The objectives of this experiment were to evaluate rumen fermentation patterns, nutrient digestibility, and ruminal methane production associated with feeding either starch or increasing levels of CDS. Apparent dry matter digestibility (DMD) increased (linear; P = 0.02) with increasing dietary CDS inclusion. Steers fed CNT increased (P = 0.01) DMD compared to those fed 10% CDS. Fat digestibility increased (linear; P < 0.01) as CDS inclusion increased, but NDF and ADF digestibility were not affected (P ≥ 0.17) by dietary treatment. Also, there was no difference (P ≥ 0.37) in ruminal methane emissions with increasing dietary inclusion of CDS. Also, increasing CDS inclusion improved DM and fat digestibility as well as overall ADG. This research provides insight into the effects of elevated protein and fat from corn coproducts on the molecular regulation of intramuscular fat development. Feeding differing levels of dietary fat and protein during the growing phase does affect intramuscular adipogenesis at the transcriptional level, but differences in gene expression were not sufficient to affect carcass quality among cattle fed coproducts in our small subset. However, coproducts with no corn fed during the growing phase resulted in carcasses with similar marbling scores to those fed corn-based growing diets suggesting that starch may not be necessary to produce high quality carcasses from early-weaned calves. Additionally, These data indicate a difference in the behavior of fat from CDS in the rumen compared to other fat supplements such as corn oil. Increased performance with increased CDS inclusion and the lack of adverse effects on ruminal metabolism and carcass traits make CDS a viable option for beef cattle diets