Effect of adding rumen-degradable protein to a dried distillers grain supplement on growth, body composition, blood metabolites, and puberty in yearling Angus and Brangus heifers

The objective of the study was to determine whether adding soybean meal (SBM), a source of RDP, to a dried distillers grain (DDG) and bermudagrass round bale silage (RBS) diet would enhance growth, body composition, and onset of puberty in Angus (n = 30; 234 ± 19 kg) and Brangus (n = 30; 252 ± 28 kg) heifers (mean age 259 ± 21 d). On d 0, heifers were assigned to (1) RBS + DDG at 0.75% BW; (2) RBS + DDG at 0.75% BW + SBM at 7.5% of DDG; or (3) RBS + DDG at 0.75% BW + SBM at 15% of DDG for 140 d. There were no treatment or breed (P > 0.05) effects for BW, BCS, or ADG by d 140. Moreover, there were no (P > 0.05) treatment or treatment × breed effects on change in body composition from d 0 to 140 for ultrasound LM area (LMA), LMA as a percentage of BW, LMA intramuscular fat, rib fat, or rump fat. Although, Angus had greater (P ≤ 0.05) LMA intramuscular fat on d 140 than Brangus. Brangus tended (P = 0.08) to have greater rump fat and LMA and greater (P ≤ 0.05) LMA as a percentage of BW than Angus on d 140. Blood metabolites were not different (P > 0.05) among treatments from d 0 to 140. Percentage of heifers pubertal by d 140 were not different (P > 0.05) between treatments. In conclusion, addition of SBM at either 7.5 or 15% of the total DDG supplement had no beneficial effects compared with DDG alone on heifer growth, body composition, or onset of puberty.