DISCUSSION

This study characterized the nutritional composition of locally available feed ingredients, evaluated four concentrate formulations varying in the proportions of cassava and tofu waste, and compared the production responses of Madura and Madrasin bulls under smallholder conditions in Bangkalan Regency. The present work provides several original contributions. First, it is among the few in vivo studies directly comparing pure Madura and Madrasin bulls that receive identical rations based on local agricultural by-products, thereby demonstrating that breed differences in feed intake and fiber utilization persist even when diets are optimized with cassava and tofu waste. Second, the systematic replacement of tofu waste with cassava waste produced predictable nutrient shifts while maintaining comparable growth performance and IOFC, offering smallholders greater flexibility in ration formulation than previously documented. Third, by conducting the experiment in adapted communal village cattle stalls rather than under research station conditions, the findings possess greater external validity for East Java smallholder systems, an aspect often overlooked in tropical feeding studies. Overall, the results demonstrate that agricultural and agro-industrial by-products, particularly cassava waste, tofu waste, and copra meal, when incorporated into balanced concentrate mixtures, can effectively support cattle production.

Nutritional characteristics of local feed resources

The nutrient composition of the feed ingredients used in this study illustrates the complementary functional roles required for formulating balanced rations in smallholder production systems. Native grass, which served as the basal forage, had low DM and CP concentrations and high ADF and NDF fractions. These characteristics are consistent with previous reports from Bangkalan Regency [19], where native grasses are abundant but frequently deficient in nutrients necessary to sustain optimum cattle performance. The high structural fiber content of native grass may reduce digestibility and limit voluntary feed intake, thereby confirming that forage alone is insufficient to support maximum growth in either indigenous or crossbred cattle.

In contrast, concentrate ingredients provided complementary nutrient fractions. Rice bran and cracked corn supplied readily digestible energy with relatively low fiber concentrations that favor ruminal degradation. Cassava waste, characterized by high NFE and TDN contents, provided rapidly fermentable carbohydrates that stimulated microbial activity when accompanied by an adequate protein supply. Because of its low CP content, cassava waste required supplementation with protein-rich ingredients such as tofu waste and copra meal. Tofu waste supplied both protein and lipid-derived energy and therefore played an important role in formulations with greater CP concentrations (C1 and C2). Although copra meal was rich in CP, its elevated structural fiber content required careful dietary balancing to prevent reductions in digestibility. Collectively, these ingredients provided complementary energy and protein fractions, supporting previous recommendations regarding the use of cassava-based diets [26, 27].

Across treatments, increasing cassava waste and decreasing tofu waste produced predictable changes in nutrient composition. CP and EE decreased progressively, whereas NFE increased and ADF and NDF increased slightly. Nevertheless, TDN remained within a relatively narrow range (73.27%–76.16%), indicating that overall dietary energy density was maintained. This nutritional consistency provided a suitable basis for evaluating physiological and productive responses to changing ingredient proportions.

Effects of dietary treatments and breed on feed intake

The concentrate formulation significantly affected DMI and the digestibility of DM and OM. Greater DMI observed in T2–T4 suggests that increasing cassava waste inclusion improved ration palatability and fermentability. Cassava waste contains rapidly fermentable starch and soluble carbohydrates that stimulate microbial proliferation and accelerate ruminal turnover, thereby increasing feed intake. These findings are consistent with previous reports demonstrating that cassava-based supplementation enhances feed intake and ruminal function in tropical cattle systems [24, 28].

Breed differences represented a major source of variation in feed intake. Madrasin bulls consistently consumed more feed across all treatments, reflecting their larger body size and greater nutrient requirements. Previous studies have shown that crossbred cattle with European genetic influence exhibit greater feed intake capacity and enhanced ruminal fermentation efficiency [19, 29]. The greater feed intake observed in Madrasin bulls was primarily attributable to increased concentrate consumption, particularly under T2–T4, suggesting that this breed may be better adapted to diets rich in fermentable carbohydrates. However, when intake was expressed relative to LW or metabolic LW, the higher intake observed in Madrasin bulls was not statistically significant, indicating that body size differences accounted for much of the variation.

Native grass intake did not differ significantly among treatments or breeds, indicating that forage consumption was constrained by the forage's intrinsic structural characteristics rather than by dietary formulation or breed. This finding emphasizes the limited contribution of low-quality forage to productive performance in smallholder systems and highlights the importance of concentrate supplementation for satisfying nutrient requirements.

Greater intake of CP, ADF, and NDF by Madrasin bulls, together with their improved utilization of fiber fractions, reflects their superior digestive capacity and greater ability to tolerate diets containing higher structural fiber concentrations. These physiological advantages likely contribute to the superior productive performance and economic returns observed in this breed.

Nutrient digestibility and digestible nutrient intake

Digestibility of DM and OM was influenced by dietary treatment, with T1 producing the highest values. This response is likely attributable to the greater CP and EE concentrations in tofu waste-rich formulations, which support microbial proliferation and carbohydrate fermentation. The importance of dietary protein in optimizing microbial activity has been extensively documented [30], and the relatively lower CP concentrations in T3 and T4 may explain the slightly lower digestibility values observed.

Despite these differences, CP, ADF, and NDF digestibility remained relatively stable among treatments. This stability indicates that moderate variations in protein and fiber concentrations did not exceed thresholds that could impair microbial efficiency. In addition, the relatively constant TDN values among diets likely maintained adequate microbial energy supply, thereby sustaining nutrient digestibility.

Breed effects on digestibility were selective. Overall, DM, OM, CP, and ADF digestibility did not differ significantly between breeds; however, NDF digestibility was significantly greater in Madrasin bulls. Although microbial populations were not evaluated in the present study, this observation supports previous reports indicating that crossbred cattle possess greater ruminal capacity and enhanced microbial activity, thereby facilitating more efficient degradation of structural carbohydrates [30]. Improved fiber digestibility constitutes an important physiological advantage in production systems where moderate- to low-quality forage predominates.

Patterns of digestible nutrient intake reflected the combined influence of feed intake and digestibility. Although digestibility values were numerically highest in T1, digestible nutrient intake was greater in T2 and T4 because of higher feed consumption. These findings highlight the importance of considering both nutrient digestibility and animal feeding behavior when evaluating nutrient availability and productive performance.

Growth performance and feed efficiency

Differences in nutrient intake did not translate into significant differences in growth performance among treatments. All four concentrate formulations supported similar LWG, indicating that variations in the proportions of cassava and tofu waste did not compromise nutrient adequacy. These results are consistent with previous studies demonstrating that properly balanced cassava-based diets can sustain satisfactory growth in tropical cattle systems [24]. The similarity in TDN values among treatments likely contributed to the absence of treatment effects on growth performance.

Although treatment effects were not significant, breed influenced growth performance. Madrasin bulls achieved a higher average daily gain (0.77 kg/day) than Madura bulls (0.68 kg/day), reflecting their superior genetic potential for growth and nutrient utilization. Similar observations have been reported for indigenous and European crossbred cattle in Indonesia [29].

FCR did not differ significantly among treatments or breeds, indicating that cattle converted feed into body weight with comparable efficiency despite differences in nutrient intake and growth. Therefore, the superior performance of Madrasin bulls was primarily attributable to greater nutrient intake and improved fiber utilization rather than to enhanced feed conversion efficiency.

Economic implications and breed conservation

Improved productive performance has limited practical significance unless accompanied by favorable economic returns. Therefore, economic performance was evaluated using IOFC. The results demonstrated that all dietary treatments were profitable and that no concentrate formulation conferred a marked economic advantage over the others. Despite differences in ingredient composition, feed costs and growth responses remained sufficiently balanced to produce similar financial returns. This finding is particularly important for smallholder farmers who operate under fluctuating feed prices and seasonal variation in the availability of agricultural by-products.

Breed exerted a significant effect on economic performance, with Madrasin bulls generating greater IOFC values than Madura bulls owing to their superior growth performance and higher market value. These findings are consistent with previous studies conducted in East Java showing that well-balanced diets combined with high-growth genotypes enhance profitability [24, 31].

The consistently favorable performance observed across treatments demonstrates the robustness of cassava-protein meal combinations in supporting growth and confirms previous findings regarding the effectiveness of cassava-based rations [18, 24]. Furthermore, the economic neutrality of the four formulations provides flexibility in feed resource utilization, enabling farmers to adjust rations according to ingredient availability without sacrificing profitability. Such flexibility represents an important advantage for smallholder production systems characterized by limited purchasing power and inconsistent feed supply.

The breed differences observed in the present study reveal a persistent productivity gap between Madura and Madrasin cattle under improved nutritional management. The advantages of crossbred cattle in terms of LWG and IOFC clearly provide strong incentives for crossbreeding in regions where Madura cattle predominate. Nevertheless, while crossbred animals offer short-term gains in productivity, long-term sustainability must also consider the conservation of the unique adaptive characteristics of Madura cattle. Economic benefits should therefore be evaluated within the broader context of national genetic resource conservation. Excessive dependence on crossbred animals could accelerate the decline in genetic purity of Madura cattle, a concern that has been highlighted previously [25].

Practical implications, limitations, and future perspectives

Collectively, the results demonstrate the considerable potential of locally available agricultural by-products to support efficient and economically viable cattle production in Bangkalan Regency. Greater utilization of these resources can strengthen feed self-sufficiency and reduce dependence on commercial feed ingredients [27, 32]. Concentrate formulations based on cassava waste, tofu waste, and copra meal provided adequate nutritional support for both indigenous and crossbred cattle, emphasizing that local feed resources remain underutilized but highly promising.

Nevertheless, several limitations should be acknowledged. The experiment involved a relatively small number of animals per treatment combination and was conducted over a relatively short period at a single location. Consequently, caution should be exercised when extrapolating the findings to broader production environments. Future studies should involve larger populations and evaluate the effects of seasonal variation in feed prices and availability. Additional investigations should also incorporate carcass characteristics and methane emissions to provide a more comprehensive assessment of production efficiency and environmental sustainability.

Overall, the integrated evaluation of feed resources, nutrient composition, intake behavior, digestibility, growth performance, and economic returns provides valuable evidence for designing feeding strategies that balance productive efficiency with the conservation of local genetic resources. Sustainable cattle production in Bangkalan Regency will depend on feeding innovations that maximize the use of local agricultural by-products while simultaneously maintaining breeding programs that preserve the genetic integrity of Madura cattle.