Eficácia de aditivos químicos e microbianos em silagem de gramíneas e avaliação de modelos de predição de consumo de matéria seca para bovinos de corte

Abstract

This study aimed (1) to carry out a systematic review and meta-analysis to evaluate the efficacy of chemical and microbial additives to silage on beef cattle and sheep performance (2) to include data on dry matter intake (DMI) of commercial herds to improve the accuracy and precision of the prediction of Model 2.1 BR Corte proposed by Azevedo et al. (2016). To respond to the first objective, systematic searches were performed using databases and scientific journals. 42 and 54 articles were selected for beef cattle and sheep, respectively. Data for all variables were grouped into subgroups according to the additive type. The treatment mean differences and 95% confidence intervals (p<0.05) were analyzed using a random-effects model. For beef cattle analysis, the use of homo-and-heterofermentative microbial inoculant mixtures (MMi) and chemical additives (Ch) increased the average daily gain (ADG) of beef cattle fed maize/sorghum silage. Homofermentative microbial inoculant (Ho), Ch, and a mixture of microbial inoculant and chemical additives also increased the ADG of beef cattle fed temperate grasses. Only Ch increased dry matter intake (DMI). Ch increased feed efficiency, and Ch and Ho increased carcass weight. The evaluated additives improved the silage fermentation process mainly via pH and ammonia nitrogen reduction. Overall, this meta analysis demonstrated that silage additives improved the ensiling process and beef cattle performance, with better results with Ch use. Due to the aerobic stability and microbiological profile analyses being carried out more in laboratory-scale silos, more studies are needed to determine these silage parameters after opening the silo at the farm scale. For sheep analysis, formic acid use reduced (p<0.05) the silage crude protein digestibility (CPD), and the ammonia nitrogen, acetic acid content and pH and increased the animal nitrogen retention, and the dry matter (DM), crude protein (CP) and, water-soluble carbohydrate (WSC) content. Enzymes use reduced (p<0.05) the silage neutral detergent fiber digestibility, CP, neutral detergent fiber (NDF), NH3–N, and acetic acid content. Ho use increased (p<0.05) the DMI, dry matter digestibility, CPD, WSC, nitrogen intake, retained nitrogen and lactic acid content and reduced the mold count, NH3–N, acetic acid content and aerobic stability of the silage. Heterofermentative microbial inoculant (Mhe) use increased (p<0.05) the DMI, carcass yield, DM, aerobic stability, and acetic acid content and reduced the NDF and acid detergent fiber, yeast, and mold counts. MMi use increased (p<0.05) the ADG, DM and yeast count and reduced the silage pH (-0.037). All additive types improved the silage quality, but only MMi improved weight gain in sheep. Mhe increased silage aerobic stability and can be used for this purpose on commercial farms. To the second objective, a correlation analysis between performance variables and DMI was performed to define the variables to be used to predict DMI. A correlation analysis between performance variables and DMI was performed. The metabolic body weight (MBW), average daily gain (ADG) and average daily gain squared (ADG2 ) variables were included in the model to generate the prediction equation using SAS software. The new prediction equation was validated according to accuracy and precision in two feedlots. After validation, the new equation was compared with eight other published equations using the software Model Evaluation System v. 3.2.3. The proposed equation for commercial feedlots was DMI = -2.1948 + 0.08338 * MBW + 3.9328 * ADG - 0.9030 * ADG2 . The new equation showed better accuracy and precision indicators for commercial feedlots. Therefore, it can make feeding systems for feedlot beef cattle in Brazil more accurate and precise.