Effects of protein source and lipid supplementation on conservation and feed value of total mixed ration silages for finishing beef cattle.
The objective of this study was to examine the conservation process and feed value of total mixed ration (TMR) silages. In Exp. 1 we evaluated the fermentation pattern and aerobic stability of TMR silages containing different protein and lipid supplementations. In Exp. 2 we compared the performance of finishing beef heifers fed those TMR silages. In both experiments, treatments were as follows: ensiled TMR with urea (U); ensiled TMR without a protein supplement at ensiling, but soybean meal supplemented at feeding to balance diet crude protein in Exp. 2 (SMnf; where the acronym nf indicates nonfermented); ensiled TMR with soybean meal (SM); and ensiled TMR with rolled soybean grain (SG). Thirty-two Nellore heifers (313 ± 8.8 kg shrunk body weight (SBW)) were blocked by initial SBW, housed in individual pens, and enrolled in the Exp.2 for 82 d. In Exp. 1, treatment without a protein supplement (SMnf) had lower content of crude protein, soluble crude protein, NH3-N, pH and clostridia count compared to U (P ≤ 0.03). Lactic acid concentrations tended to be reduced for SMnf compared to U (P = 0.09). Ethanol concentration was reduced in SG compared with SM (P < 0.01). 1,2-Propanediol concentration was increased in SMnf compared with U (P < 0.01), reduced in SM compared with SMnf (P = 0.02) and increased in SG compared with SM (P = 0.02). Dry matter (DM) loss during fermentation was low and similar among treatments (~3.7%). All silages remained stable during 10 d of aerobic exposure after feedout. Considering fermentation traits such as pH (≤4.72), NH3-N (<10% of N, except for U treatment), butyric acid (<0.05 % DM), and DM losses (<3.70% DM) all silages can be considered well conserved. In Exp. 2, diets were isonitrogenous because of soybean meal was added to SMnf before feeding. Compared with SM, cattle fed SG made more meals per day (P = 0.04) and tended to have a decreased intermeal interval (P = 0.09). Dry matter intake, average daily gain, final SBW, hot carcass weight, Biceps femoris fat thickness, and serum levels of triglycerides and cholesterol were increased for SG compared to SM (P ≤ 0.05). In brief, TMR silages exhibited adequate fermentation pattern and high aerobic stability. The supplementation of true protein did not improve animal performance, whereas the addition of soybean grain as a lipid source improved the performance of finishing cattle fed TMR silages.