Effect of adding acetic acid on fermentation quality and aerobic stability of mixed oat and alfalfa silage in Tibet

The objective of this study was to evaluate the effects of adding acetic acid on the fermentation qualities and aerobic stability of mixed silage of oat and alfalfa.The treatments were as follows:control(CA)and three treatments of different acetic acid addition ratios(0.3%,0.4%,0.5% of fresh weight).These silos were opened 30,45 and 60days after ensiling and the fermentation quality was analyzed.Then other silos were opened 60 days after ensiling and exposed to the air,and the aerobic stability was analyzed.Addition of acetic acid significantly(P0.05)decreased the pH value of mixed silage,and the pH values of 0.4% and 0.5%acetic acid addition silages were significantly(P0.05)lower than that of 0.3%acetic acid addition silages.Lactic acid(LA)contents of all acetic acid addition silages were significantly(P0.05)higher than those of control after 60 days from ensiling,however,there was no significant(P0.05)difference among all acetic acid silages.Acetic acid addition significantly(P0.05)decreased the ratio of ammonia nitrogen/total nitrogen(AN/TN),and there was a pH decline(P0.05)with increased of acetic acid addition.Water soluble carbohydrate(WSC)contents of all silages with acetic acid added were significantly(P0.05)higher than those of the control,and 0.4%acetic acid addition silages showed the highest WSC content.During the first 10 days of aerobic exposure,the values of pH and AN/TN were stable in all silages,and those of silages with acetic acid added remained lower than these of control.After 10 days of aerobic exposure,the pH value of all silages increased,and that of the control significantly(P0.05)increased.The contents of LA and WSC decreased generally during the aerobic exposure process;all acetic-acid-treated silages showed significantly(P0.05)higher LA and WSC than control,and the silage with 0.4%acetic acid added always had the highest lactic acid content.From the above results it is suggested that 0.4%acetic acid addition is appropriate.