Lactic acid bacteria (LAB) are usually employed as alfalfa silage inoculants to obtain high-quality feed for animal husbandry. However, the effects of these inoculants are still unclear and need to be studied extensively. Therefore, the objective of this meta-analysis was to quantitatively summarize published research studies that assess the effects of homofermentative (HoLAB) and heterofermentative lactic acid bacteria (HeLAB) on fermentation parameters, nutritive value, microbiological composition and aerobic stability of alfalfa silage. PubMed, ScienceDirect and Scopus have been screened for articles published from 1980 to 2018. The criteria for inclusion were: randomized and controlled trials using alfalfa silage and published in peer-reviewed journals. It was found that inoculation with LAB decreased silage pH, neutral detergent fibre, acid detergent fibre and ammoniacal nitrogen, while it increased dry matter and crude protein compared to control in the pooled raw mean difference random-effect model. Additionally, LAB inoculation decreased acetate, propionate, ethanol and butyrate concentrations, whereas it increased lactate. In addition, inoculants reduced the counts of yeasts and moulds. Lastly, LAB inoculation improved aerobic stability. To the best of our knowledge, this is the first meta-analysis that aims at comparing the application of HoLAB and HeLAB for alfalfa silage. In the pool estimate, positive effects attributable to the application of microbial silage inoculants were found in most of the evaluated parameters; supporting the importance of applying both types of inoculants to improve forage preservation for the livestock industry.

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同型发酵和异型发酵乳酸菌在苜蓿青贮中的作用：荟萃分析

乳酸菌（LAB）通常用作苜蓿青贮接种剂，以获得畜牧业的优质饲料。然而，这些孕育剂的作用仍不清楚，需要广泛研究。因此，本荟萃分析的目的是定量总结已发表的研究，这些研究评估了同型发酵 (HoLAB) 和异型发酵乳酸菌 (HeLAB) 对苜蓿青贮的发酵参数、营养价值、微生物组成和需氧稳定性的影响。PubMed、ScienceDirect 和 Scopus 已对 1980 年至 2018 年发表的文章进行了筛选。纳入标准是：使用苜蓿青贮饲料并在同行评审期刊上发表的随机对照试验。发现接种 LAB 降低了青贮饲料的 pH 值、中性洗涤纤维、酸性洗涤纤维和氨氮，而在汇总的原始平均差随机效应模型中，与对照相比，它增加了干物质和粗蛋白。此外，乳酸菌接种降低了醋酸盐、丙酸盐、乙醇和丁酸盐的浓度，而增加了乳酸。此外，接种剂减少了酵母菌和霉菌的数量。最后，乳酸菌接种提高了有氧稳定性。据我们所知，这是第一个旨在比较 HoLAB 和 HeLAB 在苜蓿青贮饲料中的应用的荟萃分析。在池估计中，在大多数评估参数中发现了可归因于微生物青贮接种剂的应用的积极影响；支持应用这两种类型的接种剂以改善畜牧业草料保存的重要性。