| 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 x 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. 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. 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. 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. (Abstract shortened by UMI.). |
