INTRODUCTION

Roughage is essential for maintaining rumen function, animal health, and fermentation efficiency in dairy cows. Its fibrous structure promotes rumen stratification, microbial colonization, and saliva secretion, which buffers ruminal pH and helps prevent acidosis [1]. However, although roughage is indispensable, its inclusion must be balanced with energy-rich dietary components to avoid excessive dilution of dietary energy, particularly in high-producing dairy cows [2]. In tropical production systems, rice straw is widely used because of its abundance, but its low crude protein (CP) content and high lignin concentration restrict digestibility and reduce nutrient availability for rumen microorganisms. Although physical, chemical, and biological treatments have been developed to improve its nutritive value, their adoption remains limited because of economic and logistical constraints in smallholder farming systems. Previous in vivo studies in small ruminants have demonstrated that monosodium glutamate by-product-treated rice straw can serve as an alternative roughage source by improving growth performance and rumen fermentation at moderate inclusion levels, whereas excessive substitution may negatively affect feed intake and digestibility [3]. Furthermore, tropical forage resources generally contain low CP and high structural fiber, particularly during the dry season when forage quality deteriorates further. These nutritional limitations constrain microbial protein synthesis, reduce feed utilization efficiency, and ultimately impair animal productivity [4, 5]. Although forage legumes and nitrogen supplementation can partially alleviate these deficiencies, there remains a need for alternative roughage resources that are nutritionally superior, economically feasible, and readily available.

The continued expansion of cassava-processing industries has generated substantial quantities of agro-industrial byproducts, including cassava pulp, cassava peels, cassava bagasse, and cassava bioethanol waste. Improper disposal of these residues may contribute to environmental pollution, whereas their utilization as feedstocks for biofuel production, biodegradable materials, activated carbon, and animal feed provides opportunities for value addition and sustainable resource utilization [6–10]. Approximately 2.5 tons of cassava bagasse and 100–300 kg of cassava peel are generated for every ton of cassava starch produced, highlighting the considerable potential of these byproducts for beneficial utilization. Nutritionally, cassava-derived residues are rich in fermentable carbohydrates while providing moderate concentrations of CP and functional fiber. Cassava roots contain 81.0–87.1 g/100 g of carbohydrates, whereas cassava leaves contain 21.2–28.4 g/100 g of protein and 16.1–22.9 g/100 g of fiber [11]. In addition, cassava pulp can be processed into dietary fiber containing up to 89.2% total fiber [12]. Anti-nutritional compounds, including cyanogenic compounds, can be effectively reduced through boiling, drying, or microbial fermentation, thereby improving the safety and feeding value of cassava-derived products for livestock [11].

Total mixed fiber (TMF) is a feeding strategy that combines multiple fibrous feed ingredients, frequently including agro-industrial byproducts, into a homogeneous ration to optimize nutrient supply in ruminant diets. TMF promotes uniform feed intake, minimizes feed sorting, and improves nutrient utilization, thereby supporting rumen health and animal performance. Previous studies demonstrated that TMF improved the digestibility of dry matter (DM), organic matter (OM), and CP, resulting in greater energy intake and increased milk production in mid-lactating dairy cows compared with conventional roughage sources [13]. Ensiling TMF with sodium diacetate further improves its nutritional quality by increasing DM and OM concentrations during storage [14]. Further-more, modification of additive type and inclusion level enables optimization of fiber quality and feed preservation. TMF also positively influences rumen fermentation. Diets with lower non-fiber carbohydrate-to-neutral detergent fiber (NDF) ratios improve growth performance and nutrient digestion, whereas excessive non-fiber carbohydrate may impair ruminal function [15]. Likewise, organic mineral supplementation in TMF has been shown to improve rumen fermentation and animal performance in beef cattle [16]. An important characteristic of TMF is its peNDF, which stimulates chewing activity and saliva secretion, thereby maintaining ruminal pH and improving fiber digestibility [17]. Higher peNDF concentrations may also modify milk fatty acid composition and consequently influence milk quality [18]. Moreover, incorporating agro-industrial byproducts into TMF further enhances its nutritional and economic value. Alkali-treated sugarcane bagasse has been reported to improve milk production and body weight (BW) gain, whereas cassava pulp supplemented with yeast waste can replace up to 75% of soybean meal without adversely affecting rumen fermentation [19]. In addition, fermentation and enzymatic bioprocessing techniques further improve protein quality and fiber digestibility of these feed resources [20].

Despite increasing interest in cassava-derived by-products as alternative feed resources for ruminants, important knowledge gaps remain regarding their application as primary roughage sources in ensiled TMF systems, particularly during early lactation. Most previous studies have evaluated TMF in mid-lactating dairy cows or investigated cassava byproducts as feed supplements, protein sources, or concentrate ingredients rather than as complete roughage replacements. Furthermore, available studies have primarily focused on dried or yeast-fermented cassava byproducts, whereas information on ensiled TMF formulated from different cassava-derived residues remains scarce [13, 21]. Consequently, the comparative effects of cassava pulp- and cassava bioethanol waste-based TMF on voluntary feed intake, nutrient digestibility, ruminal fermentation, and lactational performance have not been systematically investigated under early-lactation conditions, when nutrient demands are greatest and cows are particularly susceptible to negative energy balance. Addressing these knowledge gaps is essential to establish scientifically validated, sustainable, and economically viable roughage alternatives for tropical dairy production systems while promoting circular bioeconomy principles through the valorization of cassava-processing residues.

Therefore, this study aimed to evaluate the effects of ensiled TMF formulated with cassava pulp (TMFc) or cassava bioethanol waste (TMFe) as complete replacements for guinea grass on feed intake, apparent nutrient digestibility, ruminal fermentation characteristics, and lactational performance in early-lactating dairy cows. It was hypothesized that cassava-based ensiled TMF could effectively replace conventional guinea grass without compromising nutrient utilization, rumen function, milk yield, or milk composition while providing new comparative evidence on the feeding value of two distinct cassava-derived agro-industrial byproducts and supporting the development of sustainable feeding strategies for tropical dairy production systems.