Introduction
⌅Most studies with yeasts in ruminant feeding have been carried out using live yeasts (Marrero et al. 2015Marrero, Y., Montoya, C. A., Ruiz, O., Elías, A. & Madera, N. 2015. Growth of Pichia guilliermondii strain Levica 27 in different energy sources and nitrogen. Cuban Journal of Agricultural Science, 49(1): 47, ISSN: 2079-3480. and Marrero et al. 2020Marrero, Y., Galindo, J., Castillo, Y. & Ruiz, O. 2020. Development of yeast additives for feeding ruminants in Cuba. Cuban Journal of Agricultural Science, 54(4): 457-469, ISSN: 2079-3480.). However, the use of its hydrolyzates as additives in the ruminant feeding has been little explored, although it constitutes a promising way that make possible the activation of the ruminal microbial population, specifically the cellulolytic one, as well as the main sensitive sites of the complex ruminal ecosystem.
In S. cerevisiae, approximately 90 % of the cell wall is composed of polysaccharides, of 5-10 % of proteins and does not exceed 1 % of lipids, although the protein portion is relatively small and approximately 50 % of the cell wall is composed of glycoproteins (Klis et al. 2006Klis, F.M., Boorsma, P. & De Groot, J. 2006. Cell wall construction in Saccharomyces cerevisiae. Yeast, 23(3): 185-2002, ISSN: 1097-0061. https://doi.org/10.1002/yea.1349. and Díaz et al. 2018Díaz, A. 2018. Strategies for improving the nutritive value of conventional and organic forages. Tesis PhD. Universidad de León, Fac. de Veterinaria, Departamento Producción animal. España). According to these authors, the main components of the cell wall of these yeasts are mannan proteins and β-glucans, in more or less equal proportions, and a small amount of N-acetylglucosamine.
Among the raw matters available for the production of yeast wall derivatives, the waste from the alcohol industry (distillery creams or yeast creams, vinasses) constitutes a very aggressive pollutant for the environment. Approximately 12-15 L of wastewater/L is produced from distilled alcohol, with an annual production of 2.6 million m3. Its organic load is 60 - 150 g COD/L, approximately 1000 times greater than that permitted by environmental protection standards. These reasons justify its use to produce animal food through biotechnological procedures, which also constitutes a way to improve the environment and the ecological management of the alcohol industry.
Galindo et al. (2010Galindo, J., Diaz, A., González, N., Sosa, A., Marrero, Y., Aldana, A.I., Moreira, O., Bocourt, R., Torres, V., Sarduy, L. & Noda, A. 2010. Effect of hydrolized enzymatic product of Saccharomyces cerevisiae yeasts on the ruminal microbial population with substrate of Pennisetum prupureum vc. Cuba CT-115 under in vitro conditions. Cuban Journal of Agricultural Science. 44(3): 275–279, ISSN: 2079-3480., 2019Galindo, J., Rodriguez, M., Valenciaga, D., Milian, G., López, J.R., Díaz, A., Bocourt, R., García, R., Camacho, Y., Rondón, A.J., Perez, M., Marrero, Y., Gonzalez, N., Sosa, A. & Herrera, M. 2019. Hidrolizate de Saccharomyces cerevisiae (PROBIOLEV®): su efecto como activador de la fermentacion ruminal y produccion de leche vacuna . Premio CITMA Mayabeque.) suggested the hypothesis that the hydrolyzate obtained from these creams can be used in ruminant feeding under the concept of microbial additives. Microbial additives activate the microbial population that lives in the ruminants’ rumen, increasing the digestive use of food and the degradation of fiber (Valenciaga et al. 2019Valenciaga, D., López, J. R., Delgado, A., Galindo, J., Herrera, M. & Monteagudo, F. 2019. Effect of the enzymatic hydrolyzate of Saccharomyces cerevisiae yeast on the kinetics of ruminal degradation of nutrients of Cenchrus purpureus hybrid OM - 22 (Cenchrus purpureus x Cenchrus americanus) forage. Cuban Journal of Agricultural Science, 53(3): 249-262, ISSN: 2079-3480.). In addition, they can reduce methane production to that level and in that way provide an environmental service in two ways. These antecedents offer the possibility of thinking that the use of an enzymatic hydrolyzate of S. cerevisiae could favor the action of ruminal microorganisms in animals that intake fibrous diets. Hence, the objective of this study was to determine the effect of S. cerevisiae hydrolyzate on the ruminal microbial population of star grass.
Materials and Methods
⌅The experiment was carried out at Instituto de Ciencia Animal, San José de las Lajas municipality, Mayabeque province, Cuba, at 92 m o. s. l, 22053’ north latitude and 82002’ west longitude. The fercialitic soil, undulating, with 4.84% organic matter, 0.26 of total nitrogen, 40.59 ppm of phosphorus, 4.60 of calcium, 0.46 of magnesium and pH of 6.34.
Experimental treatments
⌅A total of three treatments were evaluated according to a completely random design in a 3x3 factorial arrangement (three treatments and three sampling hours). The treatments were: A) control with star grass, B) star grass + yeast cream and C) star grass + yeast hydrolyzate. The cream and hydrolyzate doses were 100 mL/kg of concentrate/d, equivalent to 130 mg of (β 1.3) glucan/kg of concentrate.
The hydrolyzate and yeast cream were sprayed onto the commercial concentrate for dairy cows at the indicated dose. After homogeneous mixing, the product was ready for it use.
The remainder of the experimental diet consisted on star grass. Its chemical composition was 7.26, 74.57, 10.11, 0.42 and 0.18 for CP, NDF, ash, calcium and phosphorus, % DM, respectively (AOAC 2016AOAC. 2016. Official methods of analysis of AOAC International. 20. ed. ed., Rockville MD: AOAC International., Latimer, George W. Jr., ISBN: 9780935584875, Available at: http://www.worldcat.org/title/official-methods-of-analysis-of-aoac).
The yeast cream, raw matter from which the hydrolyzate was obtained, was removed from the Jesús Rabí sugar mill distillery in Matanzas province. The characterization of the chemical composition of the hydrolyzate was carried out according to the techniques described by the AOAC (2016)AOAC. 2016. Official methods of analysis of AOAC International. 20. ed. ed., Rockville MD: AOAC International., Latimer, George W. Jr., ISBN: 9780935584875, Available at: http://www.worldcat.org/title/official-methods-of-analysis-of-aoac and DM, OM, ash and TP are indicated. The fibrous fractions were analyzed by the Goering and van Soest (1970)Goering, H. & Van Soest, P.J. 1970. Forage fiber analysis. Agricultural Hand book. US Dept. Agriculture Washington, USA, No, 379. procedure. The crude protein (CP) was determined by the Kjeldahl method. Total reducing sugars (RS) were analyzed according to the 3.5-dinitro salicylic acid (DNS) colorimetric technique, where glucose was used as a standard sugar (Bernfeld 1955Bernfeld, P. 1955. Amylases α and β. Methods in Enzymology, 1: 149-158, ISSN: 1557-7988. https://doi.org/10.1016/0076-6879(55)01021-5.). Total carbohydrates quantification (TC) was performed using the phenol-sulfuric acid colorimetric technique (Dubois et al. 1956Dubois, M., Gilles, K.A., Hamilton, J.K., Rebers, P.A. & Smith, F. 1956. Colorimetric Method for Determination of Sugars and Related Substances. Analytical Chemistry, 28(3): 350-356, ISSN: 1520-6882. http://dx.doi.org/10.1021/ac60111a017.). The values coincide with those reported by Rodríguez et al. (2017)Rodríguez, M. 2017. Evaluación de la capacidad antibacteriana de PROBIOLEV frente a bacterias patógenas. Tesis presentada en opción al título de Doctor en Ciencias Veterinarias. Matanzas, Cuba.: 19.39, 17.83, 82.17, 40.28, 38.54, 7.93 and 6.09 % of DM, ash, OM, CP, TPLW, RS, TC. Its pH was 5.56 and the TP/CP ratio was 95.68.
Experimental procedure
⌅The experiment was conducted under in vitro conditions. The Theodorou et al. (1994)Theodorou, M.K, Williams, B.A., Dhanoa, M.S., McAllan, A.B. & France, J. 1994. A simple gas production method using a pressure transducer to determine the fermentation kinetics of ruminants feed. Animal Feed Science and Technology, 48(3-4): 185-197, ISSN: 1873-2216. https://doi.org/10.1016/0377-8401(94)90171-6. technique was used. As described, 100 mL sealed bottles were used to incubate food samples in ruminal fluid and a buffer medium. In each bottle, 0.5 g of the material to be evaluated (star grass), 50 mL of the mixture consisting of rumen fluid and buffer solution in a 1:3 ratio and the concentrate in equivalent quantities with the microbial additive (hydrolyzate or cream) were introduced. The fermentation bottles were previously sterilized at 121 °C and 1.5 a.t.m. for 15 min. The procedure was carried out in a CO2 atmosphere to ensure strict anaerobic conditions. The ruminal inoculum was obtained from four crossbred cows stabled and rumen cannulated, fed a diet of forage grass and 2 kg/day of commercial concentrate and free access to water. The ruminal fluid sample was collected through the cannula, with the help of a vacuum pump. It was kept in a hermetically sealed thermo until it was transferred to the rumen microbiology and molecular genetics laboratory at Instituto de Ciencia Animal. It was then filtered through muslin. To form the mixture to be fermented, the total ruminal fluid from the four Holstein crossbred cows was used, with the aim of eliminating the animal effect.
Sampling to determine microbial populations was carried out before incubation and at 3 and 6 hours after incubation (hour 0).
Culture techniques and microorganisms counting
⌅The Hungate (1950)Hungate, R.D. 1950. The anaerobic mesophilic cellulolytic bacteria. Bacteriological Reviews, 14(1): 1-49, ISSN: 0005-3678. https://doi.org/10.1128/br.14.1.1-49.1950. culture technique was used in roll tubes and under strict anaerobic conditions. The inoculation of total viable bacteria and cellulolytic bacteria was carried out in the culture media of Caldwell and Bryant (1966)Caldwell, D.R. & Bryant, M.P. 1966. Medium without rumen fluid for non-selective enumeration and isolation of rumen bacteria. Applied Microbiology, 14(5): 794-801, ISSN: 2471-9315. https://doi.org/10.1128/am.14.5.794-801.1966., modified by Elías (1971)Elías, A. 1971. The rumen bacteria of animals fed on a high molasses urea diet. Tesis Dr. Cs. Aberdeen and Galindo (1988)Galindo, J. 1988. Efecto de la zeolita en la población de bacterias celulolíticas y su actividad en el rumen de animales que consumen ensilaje. Tesis Dr. C. Instituto de Ciencia Animal, La Habana, Cuba. For the determination of the fungal population, the Joblin culture medium (1981)Joblin, K. N. 1981. Isolation, enumeration and maintenance of rumen anaerobic fungi in roll tube. Applied and Environmental Microbiology, 42(6): 111-112, ISSN: 1098-5336. https://doi.org/10.1128/aem.42.6.1119-1122.1981. was used.
Statistical analysis
⌅For data analysis, the methodology proposed by Herrera et al. (2015)Herrera, M., Bustillo, C.W. & Torres, V. 2015. Metodología para el análisis estadístico de diferentes tipos de variables que se miden en las investigaciones que utilizan diseños experimentales relacionados con los modelos de análisis de varianza paramétrico y no paramétrico. ISBN: 978-959-7171-57-7. was used. The theoretical assumptions of the analysis of variance were tested: normality of errors using the Shapiro and Wilk (1965)Shapiro, S. & Wilk, B. 1965. An analysis of variance test for normality (complete samples). Biometrika, 52: 591-611, ISSN: 1464-3510. https://doi.org/10.2307/2333709. test, homogeneity of variance using Levene (1960)Levene, H. 1960. Robust tests for the equality of variance. Contributions to Probability and Statistics. Stanford University Press: 278-292. test for the variables total bacteria, proteolytic bacteria, cellulolytic bacteria and cellulolytic fungi. All variables failed to fulfill these assumptions.
Subsequently, data transformation was used and did not improve their fulfilling, so analysis of variance was used, according to a non-parametric completely random design in a 3x3 Kruskal-Wallis factorial arrangement. In cases where the interaction was not significant, the main effects were reported and Fisher's LSD (1935)Fisher, R. 1935. The Design of Experiments. Biometrics Journal, 20 (2): 307–321, ISSN: 1541-0420. test was applied.
For data processing, the Infostat statistical package (Di Rienzo 2012Di Rienzo, J.A., Casanoves, F., Balzarini, M.G., González, L., Tablada, M., Robledo, C.W. InfoStat versión 2012. Grupo InfoStat, FCA, Universidad Nacional de Córdoba, Argentina. URL http://www.infostat.com.ar.) was used. In cases where the interaction was not significant, the main effects were recorded.
Results
⌅The yeast hydrolyzate evaluated has glucan oligosaccharide concentrations of 3.34 ± 0.35%. The cream from which it is made has similar concentrations of the above biomolecules, but they are only found in the yeast walls and are not available to the ruminal microorganisms in the product. From these values, the dose of 100 mL/kg of concentrate is equivalent to approximately 130 mg of β (1.3) glucan/kg of concentrate.
From the analysis of the results it can be reported that there was no significant interaction between the populations of total viable bacteria, proteolytic, cellulolytic and cellulolytic fungi with the fermentation time. Table 1 shows the main effects of treatments on these microbial groups. Yeast hydrolyzate activated the total viable bacterial populations of the rumen (P=0.0088) and its population differed from that found when supplementation was not used. The yeast cream produced intermediate values of total bacteria, without showing differences between the control treatments and with hydrolyzate.
| Treatments Variables | Control | Yeasts cream | Yeasts hydrolyzate | Significance |
|---|---|---|---|---|
| Total viable bacteria, 1011 CFU/mL | 30.94b (4.48) SD=5.00 | 41.76ab (7.70) SD=7.69 | 50.30a (9.70) SD=7.23 | P=0.0088 |
| Proteolytic bacteria, 106 CFU/mL | 41.06 (14.48) SD=15.79 | 36.76 (10.56) SD=5.67 | 41.06 (12.30) SD=5.48 | P=0.3974 |
| Cellulolytic bacteria , 106 CFU/mL | 3.91b (3.74) SD=3.15 | 39.35b (5.11) SD=2.70 | 52.22a (8.48) SD=7.23 | P=0.0042 |
| Cellulolytic fungi, 105 TFU/mL | 30.80b (2.33) SD=2.66 | 39.04b (2.52) SD=1.63 | 53.17a (4.63) SD=3.38 | P=0.0009 |
() Means of the original data
a, b: means with different letters in the same row differ at p<0.05
CFU: colony -forming units, TFU: talo-forming units
In terms of viable rumen bacterial population numbers, the inclusion of doses as small as 100 mL/kg concentrate/d produces increases of 62 % of the total rumen bacterial population, which is equivalent to 19.36 x 1011 CFU/mL more bacteria, which means an increase in bacterial biomass.
The population of cellulolytic bacteria was significantly higher (P=0.0042) when was supplemented with yeast hydrolyzate compared to the cream from which it originated and to the control treatment without supplementation, which did not differ from each other (table 1). The total number of cellulolytic fungi increased (P=0.0009) with the presence of the hydrolyzate in the animals concentrate, when related to the treatment without supplementation and that supplemented with the S. cerevisiae yeast cream. The yeast hydrolyzate and the cream that gave rise to it had no effects on the population of proteolytic bacteria in the rumen.
In the research, there was not recorded effect of fermentation time on the populations of total viable bacteria, cellulolytic bacteria and cellulolytic fungi in the rumen (table 2). However, as shown in the table, proteolytic bacteria showed the lowest populations at 3 h after fermentation start of (P=0.0269).
| Indicators | Sampling time, h | Significance | ||
|---|---|---|---|---|
| 0 | 3 | 6 | ||
| Total viable bacteria, 1011 CFU/mL | 45.83 (8.96) SD=5.79 | 38.76 (6.85) SD=7.47 | 38.41 (6.07) SD=5.72 | P=0.3934 |
| Proteolytic bacteria, 106 CFU/mL | 46.87a (13.93) SD=9.71 | 31.24b (11.26) SD=13.76 | 44.89a (12.15) SD=5.63 | P=0.0269 |
| Cellulolytic bacteria, 106 CFU/mL | 43.31 (4.59) SD=2.63 | 44.46 (7.41) SD=7.45 | 35.71 (4.59) SD=3.88 | P=0.2913 |
| Cellulolytic fungi, 105 TFU/mL | 43.54 (3.59) SD=3.02 | 45.28 (3.78) SD=3.37 | 34.19 (2.11) SD=1.53 | P=0.1217 |
Legend: () Means of the original data
a, b: means with different letters in the same row differ at p<0.05
CFU: colony -forming units, TFU: talo-forming units
Discussion
⌅Many mechanisms have been described about how small doses of yeasts added to the diet of ruminants can stimulate microbial growth in the rumen (Marrero et al. 2015Marrero, Y., Montoya, C. A., Ruiz, O., Elías, A. & Madera, N. 2015. Growth of Pichia guilliermondii strain Levica 27 in different energy sources and nitrogen. Cuban Journal of Agricultural Science, 49(1): 47, ISSN: 2079-3480. and Marrero et al. 2020Marrero, Y., Galindo, J., Castillo, Y. & Ruiz, O. 2020. Development of yeast additives for feeding ruminants in Cuba. Cuban Journal of Agricultural Science, 54(4): 457-469, ISSN: 2079-3480.), a phenomenon that is linked to the quality and type of diet that the animals intake.
It has been reported that yeast cell walls may constitute approximately 30 % of the dry matter of the cell. At the structural level, it is made up of three groups of polysaccharides: mannose polymers or mannoproteins, up to 50 % of the DM; glucose polymers or β-glucans (1.3/1.6), up to 55 % of the DM and, to a lesser extent, N-acetyl-glucosamine or chitin polymers in 6 % of the DM of the cell wall (Díaz et al. 2017Díaz, A. Ranilla, M.J. & Saro, C. 2017. Influence of increasing doses of a yeast hydrolyzate obtained from sugarcane processing on in vitro rumen fermentation of two different diets and bacterial diversity in batch cultures and Rusitec fermenters. Animal Feed Science and Technology, 232: 129-138, ISSN: 2321-1628. https://doi.org/10.1016/j.anifeedsci.2017.08.011.).
One of the mechanisms that facilitate these biotechnological products is that the activating effect has its origin on the growth factors that yeasts provide for ruminal microorganisms, such as wall polysaccharides, B-complex vitamins, short-chain fatty acids (SCFA) and branched-chain fatty acids, provitamins and micronutrients (Chaucheyras-Durand 2006Chaucheyras-Durand, F. 2006. Effects and modes of action of live yeasts in the rumen. Biologia (Bratislava), 61/6: 741—750, ISSN: 1336-9563. https://doi.org/10.2478/s11756-006-0151-4. and Díaz et al. 2017Díaz, A. Ranilla, M.J. & Saro, C. 2017. Influence of increasing doses of a yeast hydrolyzate obtained from sugarcane processing on in vitro rumen fermentation of two different diets and bacterial diversity in batch cultures and Rusitec fermenters. Animal Feed Science and Technology, 232: 129-138, ISSN: 2321-1628. https://doi.org/10.1016/j.anifeedsci.2017.08.011.).
The stimulation of microbial growth, according to Chaucheyras-Durand (2006)Chaucheyras-Durand, F. 2006. Effects and modes of action of live yeasts in the rumen. Biologia (Bratislava), 61/6: 741—750, ISSN: 1336-9563. https://doi.org/10.2478/s11756-006-0151-4. and Díaz et al. (2017)Díaz, A. Ranilla, M.J. & Saro, C. 2017. Influence of increasing doses of a yeast hydrolyzate obtained from sugarcane processing on in vitro rumen fermentation of two different diets and bacterial diversity in batch cultures and Rusitec fermenters. Animal Feed Science and Technology, 232: 129-138, ISSN: 2321-1628. https://doi.org/10.1016/j.anifeedsci.2017.08.011., may be associated with the presence of two growth factors, located in the different cellular fractions of the yeast. One of them is thermolabile and has a lipid origin, and the other is thermostable, with a possible peptide origin. Rossi et al. (2004)Rossi, F., Di Lucia, D., Vicenti, P & Cocconcelli, S. 2004. Effects of peptidic factions from Saccharomyces cereviceae culture on growth and metabolism of the ruminal bacteria Megasphaera elsdenii. Animal Research, 53: 177-186, ISSN: 1627-3591. isolated two peptide fractions rich in lysine and histidine from S. cerevisiae, which were effective in stimulating the growth of the ruminal bacteria Megasphaera elsdenii, the main bacteria that ferments lactate in the rumen.
Other theories were postulated by those who found that malate present in yeasts is capable of stimulating the growth of some Gram-negative bacteria in the rumen. Newbold et al. (1996)Newbold, C.J., Wallace, R.J. & Mcintosh, F.M. 1996. Mode of action of the yeast Saccharomyces cerevisiae as feed additive for ruminants. British Journal of Nutrition, 76: 249-261, ISSN: 1475-2662. also found an increase in the population of cellulolytic bacteria and fiber digestion. All this results in an increase in microbial protein in the rumen, which helps to explain the beneficial effects observed when live yeasts or their hydrolyzates are included in the diet of animals.
Chaucheyras-Durand et al. (2008)Chaucheyras-Durand F., Walker, N.D. & Bach, A. 2008. Effects of active dry yeasts on the rumen microbial ecosystem: past, present and future. Animal Feed Science and Technology, 145: 5–26, ISSN: 2321-1628. https://doi.org/10.1016/j.anifeedsci.2007.04.019. showed the effectiveness of yeasts in influencing the growth and enzymatic activity of rumen fiber-fermenting microorganisms and reported in vitro stimulation of the fungus Neocallimastix frontalis by the provision by yeasts of thiamine and vitamin required by rumen fungi for zoosporogenesis. Also, these authors showed that yeasts stimulate the growth and enzymatic activity of glucosidase and hydrolase enzymes. The mentioned enzymes are present in fiber-fermenting bacteria, such as Fibrobacter succinogenes, Ruminococcus spp and Butyrivibrio fibrisolvens, due to the supply of nutrients and vitamins they provide to this fibrolytic population.
In general, there are few studies that analyze the effect of yeast hydrolyzates on ruminant animals. Its specific mechanisms of action are not clearly defined. Galindo et al. (2010)Galindo, J., Diaz, A., González, N., Sosa, A., Marrero, Y., Aldana, A.I., Moreira, O., Bocourt, R., Torres, V., Sarduy, L. & Noda, A. 2010. Effect of hydrolized enzymatic product of Saccharomyces cerevisiae yeasts on the ruminal microbial population with substrate of Pennisetum prupureum vc. Cuba CT-115 under in vitro conditions. Cuban Journal of Agricultural Science. 44(3): 275–279, ISSN: 2079-3480., when evaluating the effect of two levels of enzymatic hydrolyzate of the S. cerevisiae yeast on the ruminal microbial population of animals that intake Cenchrus purpureum cv. Cuba CT-115, reported increases in the populations of total viable bacteria and cellulolytic bacteria under in vitro conditions. The level of 100 mL/kg of concentrate/day was the one that allowed obtaining the greatest increase in the population of total viable bacteria.
Unfortunately, the concentration of short-chain fatty acids (SCFA) could not be determined in this experiment. In this regard, Kettunen et al. (2016)Kettunen, K., Vuorenmaa, J., Gaffney, D. & Apajalahti, J. 2016. Yeast hydrolysate product enhances ruminal fermentation in vitro. Journal of Applied Animal Nutrition, 4, ISSN: 2049-257X. https://doi.org/10.1017/jan.2015.14.1-7. and Oeztuerk et al. (2016)Oeztuerk, H., Emre, M.B. & Breves, G. 2016. Effects of hydrolysed yeasts on ruminal fermentation in the rumen simulation technique (Rusitec). Veterinární Medicína, 61(4): 195-203. https://doi.org/10.17221/8820-VETMED. reported the efficacy of two S. cerevisiae yeast hydrolyzates, which stimulated the in vitro fermentation of different substrates and increased SCFA production. This aspect, in particular, should be the subject of future studies, since with this same product Díaz et al. (2011)Díaz Reyes, A., Ranilla García, M., SaroHiguera, José., Tejido Mediavilla, C., Pérez Quintana, M. & Carro Travieso, M.D. 2011. Influence of increasy dosis of a yeast hidrolyzate obtained from sugarcane processing on in vitro rumen fermentation of two different diets and bacterial diversity in batch cultures AND Rusitec fermenters. Animal Feed Science and Technology, 232:129-138, ISSN: 1520-6882. https://doi.org/10.1021/ac601a017. obtained increases in the total concentration of SCFA, propionic and butyric acid in sheep.
More recently, Díaz et al. (2017)Díaz, A. Ranilla, M.J. & Saro, C. 2017. Influence of increasing doses of a yeast hydrolyzate obtained from sugarcane processing on in vitro rumen fermentation of two different diets and bacterial diversity in batch cultures and Rusitec fermenters. Animal Feed Science and Technology, 232: 129-138, ISSN: 2321-1628. https://doi.org/10.1016/j.anifeedsci.2017.08.011. evaluated the effect of supplementation with S. cerevisiae hydrolyzate on fermentation indicators in RUSITEC fermenters with alfalfa hay and concentrate in a 1/1 ratio. These authors observed increases in microbial growth in the rumen, especially cellulolytic bacteria, with the addition of the hydrolyzate to the diet. This result corresponds to what has been suggested in the scientific literature about the activating effect of yeast strains on populations of total viable bacteria and cellulolytic bacteria, when these strains are used as additives in diets for ruminants (Herrera 2014Herrera, M. 2014. Métodos Estadísticos alternativos de análisis con variables discretas y categóricas en investigaciones agropecuarias. Tesis en opción al título de Doctor en Ciencias Veterinarias. Instituto de Ciencia Animal. Mayabeque, Cuba. 100 p. and Casas 2018Casas, S. 2018. Saccharomyces cerevisiae y Aspergillus oryzae: estimuladores y modificadores de la fermentación y crecimiento microbiano ruminal. Artículo de revisión. Revista de Producción Animal, 30(2): 1-8, ISSN: 2224-7920.).
If it is take into account that the enzymatic hydrolyzate of S. cerevisiae is mainly composed of low molecular weight peptides, glucan and mannan oligosaccharides, vitamins, amino acids, nitrogenous bases, nucleosides and nucleotides, among other components, then it is evident that this product can exert a stimulating effect on the ruminal microbial population, just like live yeast strains, due to the presence of the mentioned substances present in the enzymatic hydrolyzate. This could directly affect the increase in the microbial population, specifically the cellulolytic one, and, as a consequence, increases in the ruminal degradability of the nutrients in the forage that the animals receive are obtained (Valenciaga et al. 2019Valenciaga, D., López, J. R., Delgado, A., Galindo, J., Herrera, M. & Monteagudo, F. 2019. Effect of the enzymatic hydrolyzate of Saccharomyces cerevisiae yeast on the kinetics of ruminal degradation of nutrients of Cenchrus purpureus hybrid OM - 22 (Cenchrus purpureus x Cenchrus americanus) forage. Cuban Journal of Agricultural Science, 53(3): 249-262, ISSN: 2079-3480.).
Conclusions
⌅The yeast produces hydrolyzate make changes in the ruminal population, increasing the populations of total viable bacteria, bacteria and cellulolytic fungi, an event that could favor the degradation of the fiber contained in star grass.