35Bacterial inoculants are known to improve quality of silage. The objectives of the present study were 36 to evaluate the effects of different types of lactic acid bacteria (LAB; L. plantarum, L. salivarius, L. 37 reuteri, L. brevis and S. bovis) inoculation (10 6 g -1 DM) on rice straw silage quality and to examine 38 these effects on ruminal fermentation characteristics, digestibility and microbial populations in an in 39 vitro condition. Inoculated rice straw was ensiled for 15 and 30 days. For in vitro study, rumen liquor 40 was obtained from two rumen fistulated mature cows fed on mixed forage and concentrate at 60:40 41 ratio twice daily. Inoculation of LAB improved (P˂0.05) the rice straw silage quality such as 42 increased dry matter and crude protein contents, decreased pH and butyric acid, and increased 43 propionic acid and LAB contents especially after 30 days of ensiling. Results from in vitro study 44 revealed that addition of LAB to the rice straw silage improved fermentation characteristics such as 45 increased total volatile fatty acids and dry matter digestibility (P˂0.05). LAB treatments also 46 decreased methane production and methane/total gas ratio after 15 and 30 days of ensiling. From the 47 rumen microbial population perspective, cellulolytic, and fungal zoospores were enhanced while 48 protozoa and methanogens were decreased by the LAB treatments. Based on these results, it could be 49 concluded that inoculating rice straw silage with LAB (especially for L. plantarum and S. bovis) 50 improved silage quality, rumen fermentation parameters and microbial populations in vitro. 51 However, in vivo studies need to confirm those effects.
52Keywords: in vitro, lactic acid bacteria, methane, microbial population, rice straw silage, rumen. 53 54 55 56 57 58 3 59 Introduction 60 Use of agricultural by-products is increasing because of limitations in food sources for livestock 61 which result in economic and environmental concerns. Rice straw, a major agricultural by-product, is 62 routinely utilized as a food source for ruminants in many regions of East and South-East Asia (Zhang 63 et al., 2017). In Malaysia, rice straw is one of the most abundant agricultural by-products (Ghazali et 64 al., 2013) . However, rice straw has very low nutritive values with low crude protein content and 65 metabolic energy for ruminants. Technologies to create high-quality animal feed from agricultural 66 residues need to be developed. Ensiling is a practical way to utilize water-soluble carbohydrates by 67 lactic acid bacteria (LAB) under anaerobic conditions to produce organic acids such as lactic acid to 68 reduce pH and to inhibit the growth of harmful bacteria resulting in good quality silage (He et al., 69 2018). Silage feeding is also a way of enhancing livestock production in the tropics especially during 70 periods of inadequate supply of fresh forage. According to the literature, LAB (homofermentative 71 and heterofermentative) which are widely used as inoculants, increased the concentration of l...