DISCUSSION

Effects of ensiled TMF on BW, feed intake, and nutrient digestibility

This study provides original comparative evidence on the use of ensiled TMF formulated from two distinct cassava-derived agro-industrial byproducts, cassava pulp and cassava bioethanol waste, as alternative roughage sources for early-lactating dairy cows. No significant differences were observed in initial BW, final BW, or ADG among the dietary treatments (p > 0.05). These findings indicate that replacing guinea grass with ensiled TMFc or ensiled TMFe did not influence body weight change during early lactation under the conditions of the present study. Although previous studies have reported improvements in growth performance following the inclusion of cassava-derived byproducts in ruminant diets [32], such responses were not observed in the present experiment. The absence of significant differences may be attributed to biological variation among animals, the relatively small experimental population, and the limited duration of the feeding trial. Therefore, no conclusion regarding enhanced growth performance can be drawn from the present findings.

Items | Guinea grass | TMFc | TMFe | SEM | p-value
Milk production, kg/day |  |  |  |  | 
Milk yield | 13.6 ± 0.83 | 15.5 ± 0.82 | 14.4 ± 0.84 | 0.97 | 0.069
4% FCM | 13.1 ± 0.79 | 15.2 ± 0.79 | 14.1 ± 0.79 | 0.85 | 0.214
Milk composition, % |  |  |  |  | 
Fat | 3.51 ± 0.37 | 3.51 ± 0.25 | 3.57 ± 0.34 | 0.17 | 0.976
Protein | 3.14 ± 0.04 | 3.13 ± 0.05 | 3.06 ± 0.07 | 0.03 | 0.510
Lactose | 4.68 ± 0.06 | 4.55 ± 0.08 | 4.53 ± 0.09 | 0.05 | 0.133
Solids-not-fat | 8.57 ± 0.15 | 8.39 ± 0.11 | 8.30 ± 0.17 | 0.08 | 0.211
Total solids | 12.08 ± 0.33 | 11.90 ± 0.28 | 11.87 ± 0.44 | 0.20 | 0.827

The greater DMI observed in cows fed the ensiled TMFe diet was noteworthy because this diet contained relatively higher fiber and lignin concentrations than the other roughage sources. This response may be associated with favorable physical and sensory characteristics of the ensiled feed, including moisture content, texture, and fermentation aroma, which likely enhanced palatability and voluntary feed intake. Furthermore, the inclusion of cassava bioethanol waste together with the ensiling process may have modified the physical characteristics of the fiber matrix, thereby reducing the physical limitations normally associated with fibrous feeds without inducing excessive rumen fill or satiety. Consequently, cows receiving the TMFe diet achieved significantly greater nutrient and ME intakes despite consuming a diet with higher NDF and ADF concentrations. These findings agree with previous studies demonstrating that cassava-derived byproducts can be successfully incorporated into dairy cow diets to improve feed intake while maintaining rumen fermentation and nutrient utilization [33, 34]. Likewise, ME intake was significantly greater in cows fed ensiled TMFe than in those fed ensiled TMFc or guinea grass, reflecting both greater voluntary feed intake and increased energy supply. These findings support previous reports indicating that cassava bioethanol waste provides a highly fermentable energy source suitable for ruminant feeding [21, 35]. Collectively, the present results suggest that ensiled TMFe represents a practical strategy for increasing nutrient intake and energy supply in early-lactating dairy cows.

Although nutrient intake differed significantly among dietary treatments, apparent digestibility of DM, OM, CP, NDF, and ADF remained unaffected (p > 0.05). These findings demonstrate that the inclusion of ensiled TMF, including TMFe with its relatively greater fiber and lignin contents, did not compromise digestive efficiency in early-lactating dairy cows. The increased DM and ME intakes observed in cows fed TMFe were therefore achieved without adversely affecting nutrient digestion. This response may reflect the capacity of the rumen microbial ecosystem to adapt to diets containing fibrous agro-industrial byproducts while maintaining normal digestive activity. Furthermore, although feed intake increased, the increase was apparently insufficient to markedly reduce ruminal retention time or impair microbial degradation of dietary nutrients. These observations are consistent with previous reports showing that appropriately processed cassava-derived byproducts can be incorporated into ruminant diets without negatively affecting nutrient digestibility [21, 33]. Overall, the present findings indicate that ensiled TMF can improve nutrient and energy intake while maintaining digestive efficiency, supporting its suitability as an alternative roughage source for lactating dairy cows.

Effects of ensiled TMF on rumen fermentation characteristics and blood metabolites

Ruminal temperature and pH remained within normal physiological ranges throughout the experiment and were not significantly influenced by dietary treatment (p > 0.05). Mean ruminal pH remained within the range considered optimal for microbial fermentation (approximately 6.5–7.0), indicating that replacing guinea grass with ensiled TMFc or ensiled TMFe did not adversely affect rumen stability or predispose cows to subacute ruminal acidosis. These findings further suggest that the inclusion of cassava-derived agro-industrial by-products as primary roughage sources can maintain a stable ruminal environment during early lactation. Similar observations have been reported previously, in which cassava bioethanol waste, including yeast-fermented products, maintained normal ruminal pH and supported stable fermentation patterns [33].

The significantly greater BUN and ruminal NH₃–N concentrations observed in cows fed the ensiled TMFc diet indicate increased ruminal nitrogen availability and greater degradation of dietary nitrogen. This response most likely reflects rapid urea hydrolysis combined with the presence of readily fermentable carbohydrates supplied by cassava pulp. Urea is rapidly converted to ammonia within the rumen, and when synchronized with an adequate supply of fermentable carbohydrates, ruminal microorganisms can efficiently utilize the released ammonia for microbial growth [36, 37]. However, elevated BUN concentrations may also indicate that nitrogen supply exceeded the availability of fermentable energy, resulting in excess ammonia absorption and subsequent conversion to urea in the liver before excretion [38]. These findings emphasize the importance of synchronizing ruminal energy and nitrogen availability when formulating TMF-based diets. Similar responses have been reported in urea-supplemented cassava diets, in which ruminal nitrogen metabolism was influenced by the balance between degradable nitrogen and fermentable carbohydrate supply [39]. Therefore, although the ensiled TMFc diet enhanced ruminal nitrogen release, optimizing the energy-to-nitrogen ratio may further improve nitrogen utilization efficiency and reduce unnecessary urea formation. Because microbial protein synthesis, microbial population dynamics, and whole-animal nitrogen balance were not determined in the present study, the efficiency with which the additional ruminal ammonia was incorporated into microbial protein could not be directly evaluated.

Differences in VFA profiles among dietary treatments further indicate that the type of cassava-derived by-product influenced ruminal fermentation pathways. The greater mean propionate concentration observed in cows fed guinea grass suggests a shift toward glucogenic fermentation compared with the ensiled TMF diets. These differences were likely associated with variation in carbohydrate composition and fermentation characteristics among the roughage sources. Diets containing ensiled TMF, which included substantial proportions of bagasse and cassava bioethanol waste, may have favored acetate-producing fermentation pathways because of their greater structural carbohydrate content. Acetate is the principal precursor for milk fat synthesis, whereas propionate serves as the major glucogenic precursor for hepatic glucose production and is therefore closely associated with lactose synthesis, energy metabolism, and milk production [40]. The relatively lower propionate concentrations observed in cows fed ensiled TMF may therefore reflect reduced starch availability together with increased fermentation of structural carbohydrates, resulting in a greater acetate-to-propionate ratio.

Previous studies have demonstrated that fermentation of cassava pulp with urea and molasses can increase ruminal propionate production and improve energy utilization [36]. In contrast, butyrate primarily functions as an important energy source for ruminal epithelial tissues and contributes to epithelial development and function. Although significant differences were observed in propionate and butyrate concentrations among treatments, these changes were not accompanied by corresponding differences in milk yield or milk composition. This finding suggests that the observed alterations in ruminal fermentation patterns were insufficient to produce measurable changes in animal performance under the conditions of the present study. Consequently, further optimization of the roughage-to-concentrate ratio and synchronization of carbohydrate fermentation characteristics may further improve VFA production patterns and enhance energy utilization in high-producing dairy cows.

Effects of ensiled TMF on milk yield and milk composition

Although milk yield was not significantly affected by dietary treatment, cows fed the ensiled TMFc diet showed a tendency toward greater milk production than those fed ensiled TMFe or guinea grass (p = 0.069). Although this tendency did not reach statistical significance, it suggests that ensiled TMFc may provide a nutritional environment that is more favorable for milk synthesis. This response may be attributed to the greater availability of rapidly fermentable carbohydrates from cassava pulp together with degradable nitrogen supplied by urea, which may have improved ruminal nutrient availability and microbial activity [36]. Similar responses have been reported previously, in which diets containing urea-treated cassava pulp enhanced rumen fermentation and were associated with improved milk production in dairy cows [32]. However, the mechanisms responsible for the tendency toward greater milk yield in the present study cannot be definitively established because microbial protein synthesis, rumen microbial populations, and metabolic indicators such as blood glucose, insulin, and VFA absorption were not evaluated. Consequently, although the observed response was likely associated with differences in nutrient availability and ruminal fermentation, further investigations are required to confirm the underlying physiological mechanisms.

The milk yields obtained in the present study were lower than those commonly reported for high-producing Holstein cows managed under temperate production systems. This difference is likely attributable to the use of Holstein Friesian crossbred cows raised under tropical environmental conditions in Thailand, where heat stress, forage quality, management practices, and genetic background may limit milk production potential. Therefore, the production levels observed in the present study are representative of practical dairy production systems in tropical regions and provide realistic information regarding the utilization of cassava-derived roughage resources under field conditions.

Milk composition, including fat, protein, lactose, solids-not-fat, and total solids, was not significantly affected by dietary treatment (p > 0.05). These findings indicate that replacing guinea grass with ensiled TMFc or ensiled TMFe did not adversely affect mammary nutrient partitioning or milk synthesis. The maintenance of normal milk composition despite differences in feed intake and ruminal fermentation suggests that both cassava-derived roughage sources adequately supplied nutrients required for milk component synthesis. These observations are consistent with previous studies demonstrating that cassava pulp supplementation maintains stable milk composition, particularly lactose concentration, while occasionally improving milk protein and fat depending on dietary formulation [41]. Similarly, diets containing yeast-fermented cassava bioethanol waste have been reported to support milk protein synthesis without altering milk fat or lactose concentrations because of their relatively high CP content and favorable fermentation characteristics [42]. Collectively, these findings demonstrate that both cassava pulp and cassava bioethanol waste can be successfully incorporated into ensiled TMF without compromising milk quality, thereby supporting their suitability as alternative roughage resources for lactating dairy cows.

Practical implications and study significance

The present findings provide novel comparative evidence regarding the utilization of two distinct cassava-derived agro-industrial byproducts as primary roughage sources within ensiled TMF systems for early-lactating dairy cows. Unlike previous investigations that primarily evaluated cassava byproducts as concentrate ingredients, protein supplements, or partial feed additives, the present study demonstrated their effectiveness as complete roughage replacements within an ensiled feeding system. Specifically, the results showed that TMFe increased voluntary feed intake and ME intake despite containing greater fiber and lignin concentrations, whereas TMFc enhanced ruminal nitrogen availability through increased NH₃–N and BUN concentrations without adversely affecting ruminal pH, nutrient digestibility, or milk composition.

These findings also have important practical implications for sustainable dairy production in tropical regions. Cassava pulp and cassava bioethanol waste are abundantly available agro-industrial residues that are frequently underutilized or disposed of as waste. Their successful incorporation into ensiled TMF provides an opportunity to convert low-value industrial byproducts into nutritionally valuable livestock feed while reducing dependence on conventional roughage resources such as guinea grass and rice straw, whose availability and quality often fluctuate seasonally. Consequently, adopting cassava-based ensiled TMF may help reduce feed shortages, lower feeding costs, improve resource-use efficiency, and support circular bioeconomy strategies by valorizing cassava-processing residues.

Study limitations and future perspectives

Several limitations should be considered when interpreting the findings of the present study. First, the number of animals per treatment was relatively small (n = 6), which may have limited the statistical power to detect treatment effects for variables exhibiting only tendency-level significance. Therefore, the results should be interpreted with appropriate caution, particularly for milk yield and other parameters approaching statistical significance.

Second, although the ensiled TMF appeared well preserved based on the absence of visible mold, abnormal odor, and spoilage, the ensiling period was limited to 7 days, and silage fermentation characteristics, including silage pH, lactic acid, acetic acid, butyric acid, and NH₃–N concentrations, were not determined. Consequently, silage quality could only be evaluated through physical observations rather than comprehensive fermentation analyses. Future studies should include detailed silage fermentation assessments to better characterize the preservation efficiency and nutritive quality of cassava-based ensiled TMF.

Third, important indicators of rumen function and dietary fiber effectiveness were not evaluated. Measurements of peNDF, particle size distribution, chewing and rumination activities, total VFA concentration, and the acetate-to-propionate ratio were unavailable. Consequently, the effects of dietary treatments on ruminal fermentation dynamics, energy partitioning, and the physical effectiveness of dietary fiber could not be comprehensively assessed.

In addition, residual hydrogen cyanide (HCN) concentrations in the ensiled diets and blood thiocyanate concentrations in the cows were not determined. Although no clinical signs of toxicity were observed during the experimental period, the absence of these measurements precluded a comprehensive evaluation of the safety of cassava-derived byproducts. Future investigations should incorporate chemical analyses of cyanogenic compounds together with physiological biomarkers to confirm the safety of long-term feeding of cassava-based ensiled TMF.

Furthermore, microbial protein synthesis, urinary purine derivative excretion, nitrogen balance, rumen microbial populations, and metabolic indicators, including blood glucose and insulin concentrations, were not evaluated. Consequently, the mechanisms underlying nitrogen utilization, microbial efficiency, and energy metabolism could not be fully elucidated. Additional studies integrating microbial, metabolic, and molecular approaches would provide a more comprehensive understanding of the biological responses to cassava-derived ensiled TMF.

The present study also did not evaluate enteric methane emissions or other environmental indicators associated with ruminal fermentation. Therefore, the potential contribution of cassava-based ensiled TMF to reducing greenhouse gas emissions and improving environmental sustainability remains unclear. Likewise, economic evaluations, including feed cost, feed efficiency economics, milk revenue, and income over feed cost, were beyond the scope of the present study. These analyses are essential for determining the practical feasibility and economic benefits of incorporating cassava-derived ensiled TMF into commercial dairy production systems.

Finally, environmental variables associated with tropical production systems, including ambient temperature, relative humidity, temperature–humidity index, and seasonal variation, were not monitored throughout the experiment. Consequently, the potential influence of heat stress and seasonal environmental conditions on feed intake, rumen fermentation, nutrient utilization, and milk production could not be separated from dietary effects.

Future studies should therefore include larger experimental populations, longer feeding periods, comprehensive silage fermentation analyses, peNDF determination, rumen microbial characterization, microbial protein synthesis, nitrogen utilization, metabolic and endocrine profiling, HCN safety evaluations, methane emission measurements, economic assessments, and environmental monitoring. Such investigations will provide a more comprehensive understanding of the nutritional, physiological, economic, environmental, and sustainability implications of utilizing cassava pulp- and cassava bioethanol waste-based ensiled TMF as alternative roughage sources for dairy production systems.