As in any other livestock system, feeding accounts for the majority of production costs in sheep production. Particularly in the tropics, the use of grains should be strategic, prioritizing categories with higher nutritional requirements, such as finishing lambs, to maximize productive performance without excessively increasing costs. This strategy is necessary because tropical forages, although characterized by high dry matter production, generally contain higher concentrations of neutral detergent fiber (NDF), acid detergent fiber (ADF), and lignin, as well as lower levels of crude protein and non-fibrous carbohydrates, resulting in lower digestibility and nutritional value than temperate forages (Riaz et al., 2025). Therefore, strategies that improve nutrient utilization and reduce feed costs are highly desirable.

Ensiling rehydrated corn grain has become an important strategy for improving starch digestibility and reducing field losses and damage caused by insects and rodents (Daniel et al., 2022). As with other types of corn silage, researchers have investigated various additives, such as inoculants, to improve fermentation and reduce spoilage in rehydrated corn silage (Silva et al., 2019). In addition, inoculants can alter the microbial profile of silages (Xu et al., 2019) and may remain active in the rumen after ingestion by animals (Weinberg et al., 2016). Thus, rehydrated corn silage could also be used as a vehicle for delivering live microorganisms to sheep, potentially improving animal performance.

In our previous study (Soares et al., 2025), we observed that rehydrated corn silage inoculated with Rhodotorula mucilaginosa and Trichoderma longibrachiatum reduced fiber content and dry matter intake in tropical hay-based diets, without affecting body weight gain. Similarly, Martins Júnior et al. (2022) showed that lambs supplemented with a yeast (Rhodotorula mucilaginosa) isolated from sheep rumen fluid had greater dry matter intake (DMI) when fed a diet containing low-quality forage. In another study, Magaço et al. (2020) evaluated the performance of lambs fed low-quality hay supplemented with a strain of the fungus Trichoderma longibrachiatum isolated from the gastrointestinal tract of sheep. The authors observed an increase in average daily gain which were 1.86 kg greater than those of unsupplemented lambs, after 42 days of confinement. However, the effects of the combined use of these two microorganisms in sheep diets have not been investigated, particularly regarding their effects on both animal performance and financial viability.

Based on our previous findings that rehydrated corn silage inoculated with Rhodotorula mucilaginosa and Trichoderma longibrachiatum, which reduced dry matter intake without affecting final body weight in finishing lambs (Soares et al., 2025), we hypothesized that this feeding strategy may also improve the financial viability of the finishing phase in feedlot systems. Thus, the present study was conducted to evaluate the effects of combined inoculation with Rhodotorula mucilaginosa and Trichoderma longibrachiatum, isolated from the gastrointestinal tract of sheep, on the financial viability of finishing lambs fed a tropical grass hay-based diet.

All animal care and handling procedures were approved by the Animal Care and Use Committee of the Universidade Federal de Minas Gerais, Brazil (protocol no. 251/2021).

The chemical composition of the rehydrated corn silages (Table 1) showed that the inoculated silage had lower neutral detergent fiber (NDF; 89.9 vs. 134.8 g/kg DM) and higher non-fibrous carbohydrates (NFC; 757.4 vs. 712.0 g/kg DM) compared with the control. Total digestible nutrients were similar between treatments (660 g/kg DM).

Growth performance data (Table 2) have been previously reported and discussed in detail in our preliminary studies (Soares et al., 2025). Briefly, lambs fed the INO diet showed lower total DMI (P = 0.003), ADG (P = 0.031), and total BW gain (P = 0.032) than those fed CTL (Table 2). No treatment effect was observed for the final BW (P = 0.666) or feed-to-gain ratio (P = 0.178). These performance parameters were used as inputs for the economic evaluation conducted in the present study.

Table 2

Item	Treatment		SEM	P-vaue
	Control	Inoculant
Dry matter intake (g/kg BW0.75/d)	102.51a	91.79b	2.219	0.0027
Initial body weight (kg)	14.43	15.08	0.806	0.1778
Final body weight (kg)	31.39	30.50	1.423	0.6660
Average daily gain (kg/day)	0.252a	0.230b	0.0073	0.0307
Total body weight gain (kg)	17.80a	16.26b	0.531	0.0320
Feed-to-gain ratio (kg)	4.607	4.492	0.0893	0.1765

SEM - standard error of the mean.

Purchase and selling prices were standardized on a live body weight basis to ensure comparability between treatments. Lambs were purchased at a fixed price corresponding to their initial body weight (US$ 38.38 per lamb; approximately US$ 2.60-2.70/kg BW) and marketed according to final live weight, generating total revenue of US$ 68.18 and US$ 66.49 per lamb for the CTL and INO groups, respectively. These values were used to calculate gross profit per lamb and per kilogram of body weight gain. Daily and total feed costs (Table 3) were lower for lambs fed the INO diet than for those fed the CTL diet (US$ 0.39 vs. US$ 0.423 per lamb/day, P = 0.005; and US$ 23.92 vs. US$ 26.22 per lamb, P = 0.004, respectively). No treatment effect was observed for total revenue (P = 0.1182). However, gross profit, expressed as US$/kg BW and US$/lamb, was greater (P = 0.011 and P = 0.025, respectively) for lambs fed the INO diet than for those fed the CTL diet. Despite the lower feed costs, final body weight did not differ between groups, supporting the economic interpretation.

Table 3

Item	Treatment		SEM	P-vaue
	Control	Inoculant
Purchase price of lambs	$38.38	$38.38	0.0001	0.185
Feed cost (US$/lamb.d)	$0.423a	$0.390b	0.010	0.005
Feed cost (US$/lamb)	$26.22a	$23.92b	0.641	0.004
Total revenue (US$/lamb)	$68.18	$66.49	1.041	0.118
Gross profit1 (US$/lamb)	$4.47b	$4.54a	0.0001	0.025
Gross profit1 (US$/kg BW)	$0.26b	$0.29a	0.009	0.011

SEM - standard error of the mean.

Additionally, the cost of the marginal factor (CMF) (Table 4) was lower in INO (P = 0.005), while the revenue of the marginal factor (RMF) did not differ between treatments (P = 0.118). Although the overall benefit-to-cost ratio (BCR) was similar between treatments (P = 0.977), the benefit-to-cost ratio of the marginal factor (BCRMF) was greater in lambs fed INO (P = 0.006).

Table 4

Item	Treatment		SEM	P-vaue
	Control	Inoculant
CMF (US$/lamb/day)	$0.423a	$0.390b	0.020	0.005
Total cost of the marginal factor (US$/lamb)	$26.22a	$23.92b	0.641	0.004
RMF (US$/lamb)	$68.18	$66.49	1.040	0.118
Net income (US$/lamb)	$4.47b	$4.54a	0.0001	0.025
Net income (US$/kg BW)	$0.26b	$0.29a	0.009	0.011
Benefit-to-cost ratio (BCR)	$1.06	$1.07	0.012	0.977
Benefit-to-cost ratio of the marginal factor (BCRMF)	$2.59b	$2.75a	0.0468	0.006

CMF - cost of marginal factor; RMF - revenue of the marginal factor; SEM - standard error of the mean.

In the present study, the combined inoculation of Rhodotorula mucilaginosa (RM) and Trichoderma longibrachiatum (TL) in rehydrated corn silage reduced DMI in lambs. The lower DMI observed in lambs fed the INO diet may be associated with greater ruminal starch availability resulting from the ensiling of inoculated rehydrated corn. During ensiling, proteolysis of the protein matrix surrounding starch granules can occur, increasing starch accessibility to ruminal microorganisms and potentially enhancing ruminal starch fermentation. This effect may be related to the hydrolytic activity of the inoculated microorganisms. Although high proteolytic activity is relatively uncommon in yeasts (Rodarte et al., 2011), previous studies have reported that fungi such as Trichoderma spp. are prolific producers of hydrolytic enzymes, including proteases (Lopes et al., 2012). Greater ruminal starch fermentability has been associated with reduced DMI in ruminants (Swingle et al., 1999; Parsons et al., 2007). This phenomenon is attributed to the hepatic oxidation theory, which posits that the satiety and hunger of ruminants are regulated by the energy status of hepatocytes (Allen et al., 2009). Greater ruminal fermentation of starch increases propionate production, which, after absorption and metabolism in the liver, stimulates hepatic oxidation and promotes satiety, thereby reducing feed intake (Junges et al., 2017). Although ruminal fermentation characteristics were not measured in the present study, the reduction in DMI suggests that inoculation may have increased starch availability compared with the conventional ensiling process used in the CTL treatment.

The increased fermentability of corn grain may also be attributed to the fibrolytic activity of RM and TL. Lee et al. (2015) documented a significant reduction in NDF content and an improvement in rice straw silage quality when inoculated with anaerobic fungi exhibiting cellulolytic activity. Similarly, Wang et al. (2019) reported enhanced silage quality and fiber degradation rates after introducing the fungus Piromyces sp. nov. from the rumen into corn silage. Consequently, the increased fiber degradation during silage fermentation likely intensified the grain’s susceptibility to breakdown in our study. This hypothesis is corroborated by the lower acid detergent fiber (aNDF) concentration observed in inoculated rehydrated corn silage (89.9 g/kg DM) compared to the control (134.8 g/kg DM).

The lower DMI observed in lambs fed INO can reasonably explain their reduced average daily gain (ADG). However, previous studies evaluating these microorganisms individually have reported different responses. Martins Júnior et al. (2022) supplemented Rhodotorula mucilaginosa to weaned lambs fed low-quality tropical hay (Urochloa decumbens) and reported increased DMI and ADG. Similarly, Magaço et al. (2020) supplemented Trichoderma longibrachiatum to weaned lambs receiving the same forage source and found no effect on DMI but an increase in ADG. These contrasting results suggest that using these microorganisms as silage inoculants may elicit different responses than their direct dietary supplementation. However, the lower DMI and ADG observed in the present study did not appear to compromise productive performance, as lambs fed the INO and CTL diets exhibited similar feed-to-gain ratios and final body weights after 63 days in the feedlot. From an economic perspective, lambs fed the INO diet generated greater gross profit (US$/head and US$/kg BW) than those fed the CTL diet. Similarly, Magaço et al. (2020) reported a 13.35% reduction in the cost of body weight production (US$/kg BW) when T. longibrachiatum was included in lamb diets. The economic value of improvements in feed efficiency relative to ADG depends largely on feed costs and market conditions (Allen et al., 2009). Accordingly, the lower feeding costs observed for lambs fed the INO diet were primarily responsible for the greater economic return. Because sheep producers have limited influence over market prices (Raineri et al., 2015), improving feed efficiency and reducing feeding costs are key strategies for increasing profitability. Therefore, the present findings suggest that inoculating rehydrated corn silage with R. mucilaginosa and T. longibrachiatum may represent a practical approach to improving the economic sustainability of feedlot lamb production systems.

Feeding fattening lambs rehydrated corn silage inoculated with Rhodotorula mucilaginosa + Trichoderma longibrachiatum improves the financial feasibility of tropical hay-based diets.