Effect of dietary starch at similar energy intake during backgrounding on subsequent finishing performance and carcass characteristics in beef cattle: a meta-analysis

Abstract Text: Intramuscular fat is reported to utilize glucose for fatty acid synthesis rather than acetate, but inconsistent results have been reported on the effect of dietary starch on marbling in beef cattle. The objective of this study was to use meta-analysis methods to determine the effect of dietary starch during backgrounding on subsequent finishing performance and carcass characteristics in beef cattle. Following a literature search, 14 studies were identified where diets differing in grain inclusion level were fed to normal-weaned steers such that energy intake was controlled for similar ADG. All treatments within a study were fed the same finishing diet. Treatments within study were classified as low, medium, or high starch based on grain inclusion level of the diet.  This resulted in subdividing the dataset to analyze comparisons of high (HI1) vs. medium (MED) starch (9 studies) and high (HI2) vs. low (LOW) starch (7 studies); not enough studies had a medium vs. low starch comparison. Data were analyzed using a linear mixed model (Proc Mixed of SAS) that included diet as a fixed effect and intercept as a random effect with the unstructured option and study as the subject. Least square means were computed using the inverse of the squared standard error for the dependent variable as a weighting factor. The mean grain inclusion level, calculated NEg concentration, and growing phase ADG were 79.4 and 45.2% of DM, 1.42 and 1.02 Mcal/kg DM, and 1.07 and 1.12 kg/d for HI1 and MED, respectively, and were 72.8 and 16.4% of DM, 1.42 and 1.03 Mcal/kg DM, and 1.30 and 1.26 kg/d for HI2 and LOW, respectively. Growth rate, DMI, and G:F were similar (P > 0.05) between HI1 and MED and HI2 and LOW. Likewise, HCW, LM area, and 12^th-rib fat thickness were similar (P > 0.05) between HI1 and MED and HI2 and LOW.  Marbling score was similar (P > 0.05) between HI1 and MED (427 and 436 ± 17; 400 = Small⁰⁰) and HI2 and LOW (443 and 434 ± 19). These data indicate that dietary starch inclusion level at similar energy intake during the growing phase does not impact subsequent finishing performance or carcass characteristics.

Keywords: backgrounding, dietary starch, marbling