体外产气法评价不同物理状态苜蓿干草营养价值的研究

Determination of The Nutritional Value of Alfalfa Hay at Different Physical States by in Vitro Gas Production Methods

试验旨在研究体外产气法评价不同物理状态发酵底物对产气量、pH、氨态氮、微生物蛋白和挥发性脂肪酸产量的影响。试验采用单因素试验设计,即选择粉碎至0.425 mm苜蓿干草和切短至20 mm苜蓿干草作为发酵底物,每组设置5个重复,培养期为72 h。结果表明:20 mm苜蓿干草产气速率极显著低于0.425 mm苜蓿干草(P<0.01),但两组72 h累积产气量和理论最大产气量差异不显著(P>0.05);两组p H都在正常范围波动;4 h以后0.425 mm组氨态氮(NH3-N)浓度均低于20 mm组,24 h以后两组NH-N浓度有极显著差异(P<0.01);微生物蛋白含量两组均呈现上升趋势,但两组间没有显著差异(P>0.05);乙酸、丙酸、丁酸、戊酸和总挥发性脂肪酸浓度,两组都呈现上升趋势,发酵24 h前,除丁酸外,0.425 mm组均显著低于20 mm组(P<0.05),发酵48 h后,各组总挥发性脂肪酸浓度都未出现显著性差异(P>0.05)。综上所述,应用体外产气法评价苜蓿干草饲料时,发酵底物物理状态会影响其发酵参数与产气量,应选择20 mm长度作为发酵底物更能真实准确评估饲料真实消化营养价值。

This study aimed to investigate the effects of fermentation substrates in different physical states on gas production,pH value,ammonia nitrogen,microbial protein and volatile fatty acid production by using in vitro gas production method.The single factor experiment design was used in this experiment,alfalfa hay crushed to 0.425 mm and alfalfa hay cut to 20 mm were selected as fermentation substrates.Each group had five replicates,and the culture period was 72 hours.The results showed that:the gas production rate of 20 mm alfalfa hay was significantly lower than that of0.425 mm alfalfa hay (P<0.01),but there were no significant differences in cumulative gas production of72 hours and theoretical maximum gas production between the two groups (P>0.05).The p H values of two groups fluctuated within the normal range.After 4 hours the concentration of NH-N in 0.425 mm group was lower than that in 20 mm group.After 24 hours of fermentation,the concentrations of NH-N in two groups were significantly different (P<0.01).The content of MCP in both groups showed an increasing trend.However,there was no significant difference in MCP concentration between 0.425 mm group and 20 mm group (P>0.05).The concentrations of acetic acid,propionic acid,butyric acid,valeric acid and TVFA in both groups showed an upward trend.In the first 24 hours of fermentation,except butyric acid,the concentrations of VFA in 0.425 mm group were significantly lower than those in 20 mm group (P<0.05).After 48 hours of fermentation,the concentrations of VFA in all groups showed no significant difference (P>0.05).In conclusion,when using in vitro gas production method to evaluate alfalfa hay feed,the physical state of fermentation substrate could affect its fermentation parameters and gas production,the 20 mm length of fermentation substrate should be selected to evaluate the true digestive nutritional value of feed more accurately.