Yeasts are unicellular eukaryotic organisms of the kingdom Fungi that ferment carbohydrates (1–3). Yeasts have been used in animal feed for more than 100 years, and the use of yeasts in animal feed has increased in recent years. There are more than 500 cataloged species of yeasts, and among them the most studied in animal nutrition is Saccharomyces cerevisiae, which has approximately 4000 registered strains (4). The observed responses regarding the use of S. cerevisiae in animal feed depend on the dosage offered to the animal, the type of strain used, the animal’s diet, feeding management, and the animal’s physiological characteristics (1, 5, 6).

Commercially available products containing yeasts used in ruminant nutrition are composed of a mixture of live cells or mixtures of different proportions of living and dead yeasts in the presence of the culture medium, called yeast culture. These products are based on S. cerevisiae, and differ in the chosen strains and other characteristics, such as concentration (colony forming units, CFU/g), cell viability, and processing. As different products differ in these characteristics, discrepant effects of such supplements are found in different studies.

Although there are many possible mechanisms of action for yeast, the action of yeast with regards to its effects on performance of ruminants is still not sufficiently clear. Positive effects of live yeast supplementation on the ruminal environment have been attributed to changes in the microbial population, providing an increase in cellulolytic bacteria, and bacteria that consume lactic acid (7, 8), and prevent the reduction of ruminal pH (9).

Yeasts are unicellular microorganisms that act in different biological processes, such as fermentation. In general, yeasts are involved in the production of volatile fatty acids, which are considered the main source of energy for buffaloes. In addition, yeasts help to prevent acidification in the rumen, as well as producing microbial proteins that are subsequently absorbed by the animal, contributing to the animal’s proper nutrition (6).

As for the specificity of the different buffalo diets, it is essential to take into account the fact that buffalo are herbivores and have a digestive system adapted to fermenting fibers. In general, their diet is based on grasses and leaves found in different places, especially in flooded areas. Supplementing cattle with specific strains of live yeasts has resulted in increased digestibility of (mainly low quality) fiber (10, 11) and increases in dry matter consumption (12, 13). Furthermore, Chaucheyras-Durand et al. (7), reported that the main beneficial effect of live yeasts with regards to fiber digestibility is the ability of living yeast cells to reduce ruminal oxygen, which improves the ruminal environment and allows other microorganisms to colonize the rumen and digest fiber.

Although there are several studies using yeast supplementation in the bovine diet, research on the use of yeast in the buffalo diet is scarce. However, some studies on yeast supplementation in the diet of buffalo calves have found signs of increases in the bacterial ruminal population through modified production of short chain fatty acids, lower acetate and propionate ratios (14), and improved feed efficiency in young animals consuming diets based on grass hay (15, 16). Thus, the objective of this study was to evaluate the effect of S. cerevisiae strain KA500 supplementation on feed performance, feed efficiency, and digestion ability in feedlot buffaloes.

The data on dry matter intake (DMI), feed efficiency in kilograms per kg of dry matter intake, plasma urea nitrogen (PUN) concentrations, plasma glucose concentrations, the allantoin creatinine concentration, allantoin creatinine ratio of urine, and morphometry of buffaloes supplemented with live yeast (S. cerevisiae) or not (control) are presented in Table 2. Although not statistically different, yeast supplementation reduced the daily dry matter intake and percentage of live weight of buffaloes.

The efficiency in gain/kg CMS, and the morphological measurements of height at the withers and rump, and thoracic perimeter, as well as body condition score (BCS) were not affected by yeast supplementation (Table 2). The mean BCS values were 3.8 and 3.7 for buffaloes supplemented with yeast and buffaloes in the control treatment, respectively.

No effect of yeast supplementation on plasma urea nitrogen (NUP) concentrations was found (Table 1 and Figure 1). The mean NUP concentration, assessed throughout the day, was between 14.5 and 19.0 mg/dL. The highest NUP concentrations were found 3 h after the morning and afternoon meals.

Purine derivatives (allantoin and creatinine) were not affected by yeast supplementation (Table 2). The microbial protein synthesis estimated by the relationship between allantoin and creatinine concentration in urine was higher when buffaloes were supplemented with yeast, although this was not statistically significant.

There were no significant differences in plasma glucose concentrations in buffaloes supplemented with yeast or buffaloes in the control group (Table 2). Plasma glucose concentrations were higher 8 h after the first feeding (Figure 2).

Dry matter digestibility (DMd) and organic matter digestibility (OMd) were lower (p < 0.05) in buffaloes supplemented with yeast (Table 3). However, the digestibility of neutral detergent fiber (NDFd) and digestibility of non-NDF organic matter (nNDFOMd) were not affected by yeast supplementation. Thus, in this study, supplementing buffaloes with live yeast did not result in beneficial changes in the digestion of fiber.

Data on the performance of buffaloes supplemented with live yeasts or not (control) is presented in Table 4. There was no effect of yeast supplementation on total buffalo weight gain. However, there was a tendency (p = 0.07) for daily weight gain to be lower in buffaloes supplemented with yeast than in buffaloes in the control treatment.

The carcass yields found in this experiment were 44.5 and 43.5% for buffaloes supplemented with yeast and buffaloes in the control treatment, respectively (Table 4). This indicates that carcass yields increased when buffaloes were supplemented with yeast in relation to the control treatment, although this difference was not statistically significant.

There was no effect of yeast supplementation on time spent chewing (Table 5). The time taken for first intake in minutes was not affected by yeast supplementation.

Although we did not find a statistical difference in DMI, there was a reduction in consumption (Table 2), which agrees with Malik and Bandla (21) and Ullah et al. (22) that reported a reduction in dry matter intake (DMI) in buffalo calves supplemented with live yeast (S. cerevisiae). Already, Di Francia et al. (15) found no effect of yeast on dry matter intake in buffalo calves.

The mean BCS values were 3.8 and 3.7 for buffaloes supplemented with yeast and buffaloes in the control treatment, respectively, indicating that the buffaloes were in good body condition. The values of thoracic perimeter found in this study, both in buffaloes supplemented with yeast and buffaloes in the control treatment, were higher than the values reported in previous studies.

Evaluation of NUP concentrations is a way to monitor the efficiency of protein use in the diet, resulting in indicators of the nitrogen-energy ruminal balance. The fact that yeast supplementation did not affect the plasma NUP concentration can be explained by the lack of effect of yeast on the digestibility of dietary organic matter. A similar result was reported by El-Ashry et al. (23), who found that the urea concentration in plasma of lambs was not significantly affected by yeast supplementation. Buffaloes are less efficient at using N on a high protein diet. Naveed-ul-Haque et al. (24) observed an increase in PUN from 21.1 to 26.6 mg/dl when the dietary protein content of milk buffaloes increased from 11 to 14.2% based on dry matter.

This trend of lower weight gain can be explained by the reduction in the digestibility of organic matter. Growth-related responses to yeast supplementation varied from no significant effect on mean daily gain to increases of more than 20% (25). This could be due to the amount of yeast provided to buffaloes in this study, which was higher than the amount used in most previous studies, or this could be due to the strain used, the animal diet, feed management, the physiological characteristics of the buffaloes (1, 7), or thermal stress, which may have contributed to the reduction in CMS, affecting the daily weight gain. Differently from our study, that we found no difference between the treatment in plasma glucose levels, Singh et al. (26) reported increases in plasma glucose concentrations in buffaloes supplemented with yeast.

In this study, supplementing buffaloes with live yeast did not result in beneficial changes in the digestion of fiber. Several studies conducted in cattle have shown that strain type, diet, and yeast dosage may affect the effect of yeast supplementation on performance and nutrient digestibility in cattle. According to Calabro et al. (27), buffaloes are more capable of digesting feed with higher fiber contents. Thus, supplementing buffaloes with yeast may not have resulted in improvements in fiber digestibility, as buffaloes are already able to efficiently digest fiber.

Reddy (28) found no effects supplementing buffaloes with 5 g of yeast on nutrient digestibility of DM, OM, NDF. Kumar et al. (29) conducted an experiment with buffalo calves supplemented with S. cerevisiae strain CNCM I-1077 at a rate of 0.25 g/calf/day and found that yeast supplementation resulted in a significantly higher digestibility of DM, EE, OM, CP, ADF, and NDF, compared to the control diet. In another study by Kumar et al. (30) on the effect of yeast culture supplementation, buffaloes were supplemented with S. cerevisiae (0.5 g/buffalo/day; 1.5 × 10⁸ cfu/kg) and reported that dry matter intake (kg/100 kg body weight), CP digestibility, total digestible nutrients (TDN), nutrient digestibility, and crude fiber fractions were not affected by yeast supplementation as compared to the control diet.

Previous studies found that the addition of 0.25 to 5 g/buffalo/day resulted in improvements in the performance of buffalo calves (29). This suggests that the addition of 10 g/buffalo/day (2.0 × 10¹⁰ cfu/kg) of yeast (S. cerevisiae) in this study may have been high, which may limit consumption, reduce nutrient digestibility, and consequently affect the daily weight gain.

The final body weight (FBW), carcass yield (%), and carcass weight (kg) increased during the study period, but these increases were not statistically significant. The tendency for daily weight gain to be lower in buffaloes supplemented with yeast than in buffaloes in the control treatment can be explained by the reduction in the digestibility of organic matter. Growth-related responses to yeast supplementation varied from no significant effect on mean daily gain to increases of more than 20% (25). This could be due to the amount of yeast provided to buffaloes in this study, which was higher than the amount used in most previous studies.

The carcass yields increased when buffaloes were supplemented with yeast in relation to the control treatment, although this difference was not statistically significant. The carcass yields found in this study are smaller than those reported in most other studies, (49.9 to 51.7%) (31). The lower carcass yield found in buffaloes is a consequence, mainly, of the greater weights of leather and heads in these animals (32). In other cases, there is a large variation between animal weights, and the breed effect is confounded by the effect that body weight has on carcass yield. The lower carcass yield of buffaloes in our experiment can be explained by the lower age of the animals (approximately 14 months at slaughter).

The absence of effect, by yeast supplementation, on time spent with chewing and the time taken for first intake in minutes may be correlated with the digestibility of NDF, which also did not change with the supplementation of live yeasts. The higher or lower digestibility of NDF could cause an increase or reduction in the time of first intake, respectively. A greater digestibility of NDF would reduce the physical limitations of consumption (33), which would lead to a longer intake time. Devries and Chevaux (34) reported no effect of yeast on time spent on ingestion in dairy cows.

The limitations of this study were the length of time it took to evaluate the action of the yeasts and the number of animals, so we suggest that new studies be carried out with a larger number of animals, with more time to evaluate the yeasts and with more variables.

In conclusion, supplementing buffaloes with 10 g (2 × 10¹⁰ cfu/kg of viable cells) of S. cerevisiae strain KA500 did not significantly affect consumption, weight gain, and feed efficiency. There was a trend for daily weight gain to be lower in buffaloes supplemented with yeast, which can be explained by a reduction in organic matter digestibility. The dose of live yeast in buffalo diets appeared to be high, compared to the doses used in previous studies. However, yeast cultures do not act similarly when added to any diet. This study shows that the mode of action of yeasts is dependent on the strain and dosage used, diet, food handling, physiological characteristics of animals, and animal health. It is recommended that future studies investigate different dosages, with the addition of different yeasts or other potential additives that have potential effects on the digestion and metabolism of buffalo.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

This study was submitted to and approved by the Ethics Committee for the Use of Animals (CEUA) of the Universidade Federal do Amazonas (UFMA), under number 014/2017. The study was conducted in accordance with the local legislation and institutional requirements.

MF: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Software, Validation, Writing – original draft, Writing – review & editing. WS: Formal analysis, Investigation, Methodology, Validation, Writing – original draft, Writing – review & editing. AC: Data curation, Investigation, Methodology, Supervision, Validation, Writing – original draft, Writing – review & editing. EC: Conceptualization, Data curation, Investigation, Methodology, Supervision, Writing – original draft, Writing – review & editing. ÍC: Investigation, Methodology, Supervision, Writing – original draft, Writing – review & editing. SD: Data curation, Investigation, Methodology, Writing – original draft, Writing – review & editing. RL: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing.