The Use of urea levels in sorghum silages subjected to aerobic exposure

Abstract

The work aimed to evaluate the effects of urea levels and aerobic exposure on the chemical-bromatological composition and aerobic stability of sorghum silages. The sorghum cultivar used was Santa Elisa. The experimental design used was completely randomized, in a 5 x 2 factorial scheme, consisting of five levels of urea - 0; 0.5; 1.5; 2.5; and 3.5% based on dry matter (DM) - and two times of aerobic exposure 0 and 72h. There were four replications per treatment, totaling 20 experimental silos. For data relating to gas losses, DM losses and recovery, only the time of 0h was used. After 100 days, the silos were opened, and sensory evalua-tion, chemical-bromatological analysis and evaluation of aerobic stability were carried out. The aerobic stabil-ity data were subjected to descriptive analysis and the chemical and chemical composition averages were analyzed using the SAS computer program. The means were subjected to analysis of variance using PROC GLM, where linear and quadratic contrasts were tested, considering a probability of 5% (p < 0.05) as the level of statistical significance. The addition of urea promoted an effect (p < 0.05) for DM, mineral matter in relation to the time of 72h of anaerobic exposure; crude protein (CP) showed an increasing effect (p < 0.05) at the time of 0h, presenting increase in levels reaching 7.5%. For ether extract, nitrogenous compounds insoluble in the acid detergent and protein insoluble in the acid detergent, the addition of urea promoted an effect at both times. Aerobic stability remained stable up to 108h of aerobic exposure. In conclusion, the addition of urea promoted changes in the chemical-bromatological composition of the material, increased the CP content and affected the fibrous fractions, without inhibiting the growth of undesirable microorganisms in silages exposed for 72h. The DM and ammonia nitrogen contents in silages exposed for 72h were outside the desired value for good quality silage, making it unfeasible for the animal to consume. Regarding stability, the silages remained for up to 84hs after opening the silos, having to be discarded after this time. Given the results obtained, the use of urea in sorghum silages that need to be exposed for a medium and long period of time is not recommended.