Effects of Adding Propionic Acid on Fermentation Quality and Aerobic Stability of Mixed Silage of Hullessbarley Straw and Perennial Ryegrass in Tibet

This study was carried out to evaluate the effects of adding propionic acid on the fermentation quality and aerobic stability of mixed silages of hullessbarley straw and perennial ryegrass.There were three treatments of different propionic acid addition ratios(0.3%,0.4%or 0.5%of fresh weight) plus a control.Silos were opened on 30 th day of ensiling,six silos per treatment were used for fermentation quality determination,and other silages were exposed to the air for 12 days and subjected to an aerobic stability evaluation.The results showed that the fermentation quality of all treatments were well.There were no significant difference in pH value,lactic acid and dry matter contents among all treatments,however,lactic acid /acetic acid and water soluble carbohydrate in propionic acid treatments(except PA3) were significantly higher than control(P0.05).The propionic treatments showed significantly lower ammonia-N/total-N and butyric acid content compared with control(P0.05).During aerobic exposure,the pH value of0.4%and 0.5%propionic acid addition increased more slowly than that of control and 0.3%propionic acid addition silages.The lactic acid,water soluble carbohydrate and dry matter content decreased gradually during aerobic exposure,and increased with propionic acid addition ratio.The value of ammonia-N/total-N and butyric acid content of all silages increased during aerobic exposure,and these of 0.4%and 0.5%propionic acid addition silages were always significantly lower than control and 0.3%addition silages(P0.05).These results indicated that adding 0.4%or above propionic acid could improve the fermentation quality and aerobic stability of the mixed silage.