Livestock systems at Region Aysen del General Carlos Ibanez del Campo depend on forage conservation during the spring-summer season, generally with low nutritional quality to animal requirements. To reduce nutrient loss, additives are commonly used, being spent brewery yeast a potential additive. Therefore, a study was carried out with the inclusion of two spent brewer's yeast (Lager and Ale) as an additive in pasture mini silos compared to two commercial additives (SiloSolve MC (TM) and Josilac grass (TM)) and mini silo without additive. It was observed that spent brewer's yeast has a negative effect on crude protein and metabolizable energy, contents that decreased to 9.8% and 2.5%, respectively, compared to control. However, Ale yeast declined faster and maintained lower pH levels below 4.1. Spent brewer's yeast do not improve nutritional quality, however decreased pH levels of pasture silage. Therefore, it should be noted that the effect of spent brewer's yeasts has been insufficiently evaluated. Thus, is still a lack of trials within large scale of silage conservation and its effects on animal feed performance.