INTRODUCTION

Indonesia’s smallholder cattle production system is a critical pillar of national food security, rural livelihoods, and the preservation of genetic resources. Smallholders contribute approximately 90% of domestic cattle production, yet national beef output meets only about 45% of total demand, creating a persistent supply deficit that increases reliance on imports [1, 2]. This structural imbalance imposes considerable pressure on rural producers, who typically operate on limited land and capital and whose productivity is constrained by feed scarcity, fluctuating input costs, and restricted market access [3]. The dual challenge of increasing production while maintaining livelihood stability underscores the importance of strengthening smallholder feeding systems.

A central limitation in Indonesian smallholder cattle systems is the inadequate year-round access to high-quality feed. Feed shortages are intensified by competition for land, seasonal variability, and the high cost of commercial concentrates, which many smallholders cannot afford [2]. Consequently, producers rely heavily on low-quality natural pastures and crop residues that provide insufficient nutrients to sustain optimal growth, particularly in intensively fattened cattle. This nutritional gap suppresses average live weight gain (LWG), compromises reproductive performance, and adversely affects animal health. Studies have demonstrated that introducing improved feed resources, such as forage tree legumes and high-quality silage, yields substantial gains in smallholder systems. For example, the use of Leucaena has been reported to double cattle growth rates under traditional management [4, 5]. Despite their potential, the adoption of such innovations remains uneven because of knowledge gaps and limited local processing capacity.

Indigenous cattle breeds play an essential role in this context, contributing not only to household income but also to the ecological and cultural resilience of livestock-based livelihoods. Breeds such as Madura cattle are deeply integrated into local production environments and are valued for their adaptability to harsh tropical conditions and tolerance to parasitic challenges. These animals can maintain productivity under limited feed availability [6, 7], making them indispensable to smallholder production systems. Madura cattle are small, hardy, and heat-tolerant, typically reaching market weights of 200–300 kg, whereas Madrasin (Madura × Limousin) crossbreds are larger, faster growing, and more feed-efficient, often achieving market weights of 350–450 kg. Although Madura cattle excel in adaptation to tropical environments, Madrasin cattle have been selected primarily for enhanced productivity [8]. Consequently, safeguarding indigenous genetic resources has become increasingly important because uncontrolled crossbreeding threatens population integrity and long-term breed sustainability.

Another important challenge involves the strategic utilization of agricultural by-products as alternative feed resources. Across Southeast Asia, farmers routinely incorporate by-products derived from rice, palm oil, fruit, and tuber processing into ruminant diets, thereby providing inexpensive sources of fermentable energy and structural fiber [3, 9]. In Indonesia, particularly in East Java, abundant agro-industrial residues, including cassava waste, tofu waste, rice bran, and copra meal, remain underutilized due to limited information on their nutritional value, processing requirements, and optimal inclusion rates. Improving the utilization efficiency of these resources is essential for reducing feed costs while maintaining adequate nutrient supply. Previous studies have shown that appropriate processing and ration formulation can markedly improve the nutritive value of agricultural by-products and stabilize feed availability throughout the year [9–11].

The incorporation of local by-products into smallholder feeding systems aligns with Indonesian national strategies to reduce dependence on commercial concentrates and imported feed ingredients. Nevertheless, the successful adoption of by-product-based feeding systems requires a comprehensive evaluation of their nutritional characteristics, effects on feed intake and digestibility, and economic feasibility. Cassava waste, particularly in the form of ground tubers, provides abundant fermentable energy but contains limited crude protein (CP) and may contain anti-nutritional compounds such as cyanogenic glycosides. In contrast, tofu waste is rich in protein and lipids but may contain anti-nutritional substances, including trypsin inhibitors, phytates, and phytoestrogens, thereby necessitating careful ingredient balancing to maintain ruminal function and microbial protein synthesis. No previous study has simultaneously manipulated the proportions of cassava waste and dried tofu waste in a single concentrate formulation while comparing responses across specific cattle breeds. Therefore, understanding the interactions among these ingredients in rations is essential for optimizing nutrient utilization, ruminal fermentation, and growth performance.

Breed-specific responses to by-product-based diets represent another important aspect. Crossbred cattle, such as Limousin-influenced Madrasin bulls, generally exhibit superior growth performance compared with indigenous breeds due to greater rumen capacity, enhanced microbial activity, and improved energy-partitioning efficiency [12–14]. These physiological advantages are often associated with greater feed intake, improved fiber digestibility, and higher average daily gain under supplemented feeding systems. Although crossbreds provide greater short-term economic returns, their higher nutrient requirements and lower adaptability to resource-constrained environments may limit their suitability for some smallholders and accelerate the erosion of indigenous Madura cattle genetic resources. Empirical information comparing the productive and economic performance of crossbred and indigenous cattle fed locally available feed resources under smallholder conditions remains scarce. Consequently, comparative evaluations are needed to quantify breed differences under standardized feeding regimes based on local by-products.

Despite increasing interest in the use of agricultural by-products in tropical livestock production, several important knowledge gaps remain. First, direct comparisons between indigenous Madura cattle and Madrasin crossbreds receiving locally formulated rations are limited, thereby restricting evidence-based decision-making for farmers and breeding programs. Second, previous studies have generally investigated cassava waste and tofu waste separately, leaving uncertainty regarding their combined effects on feed intake, nutrient digestibility, growth performance, and profitability. Third, most studies have focused on either nutritional characteristics or productive responses alone and have rarely integrated feed characterization, controlled feeding experiments, and economic evaluation within a single framework. Moreover, information generated under practical smallholder production environments remains limited. These shortcomings hinder the development of scientifically validated feeding strategies that can improve productivity while supporting the conservation of indigenous cattle genetic resources.

Addressing these limitations is essential for improving the productivity and sustainability of Indonesian smallholder cattle systems. Therefore, the present study was conducted to characterize the nutrient composition of locally available feed ingredients and to evaluate the effects of different inclusion levels of cassava and tofu waste on feed intake, nutrient digestibility, growth performance, and economic returns in Madura and Madrasin bulls. Bangkalan Regency was selected as the study area because it represents the traditional center of Madura cattle production and provides abundant access to agricultural by-products, although optimized feeding recommendations remain limited. By integrating detailed feed characterization, in vivo animal responses, and economic analysis based on income over feed cost (IOFC) within a 2 × 4 factorial design under communal smallholder conditions, this study provides novel and location-specific evidence for developing flexible, low-cost, and sustainable feeding strategies that simultaneously enhance productivity and support indigenous breed conservation.

It was hypothesized that optimizing the ratio of cassava to tofu waste in a standardized concentrate would improve nutrient intake, digestibility, and growth performance. Furthermore, it was anticipated that Madrasin bulls would exhibit superior growth performance because of their physiological advantages, whereas indigenous Madura cattle would maintain competitive economic efficiency based on IOFC when fed locally available agricultural by-products. Ultimately, this study contributes to broader efforts to strengthen feed self-sufficiency, improve cattle productivity, and safeguard indigenous cattle resources in Indonesia’s evolving livestock sector. The findings are expected to support policy development, extension programs, and on-farm decision-making, thereby helping smallholders overcome feed shortages, increasing input costs, and crossbreeding pressures while promoting more sustainable, profitable, and resilient production systems.