Single cell protein is the edible unicellular microorganism. The microorganisms like fungi, yeast, bacteria etc. are extensively being employed in fermentation of many kinds of waste materials to get more protein12. In our study we observed an increase in protein contents from 5.40% to up to 34.34% after addition of S. cerevisiae as protein supplement even after 96 hours of incubation. Our results were supported by others34, 35 who also reported an increase in protein contents after S. cerevisiae supplementation. In a study performed by Darwish et al.36, S. cerevisiae was used in combined mixture to upgrade the nutritional value of maize stalks using solid state fermentation technique. The crude protein increased from 3.60–11.80% when S. cerevisiae was used as biological additive material after incubation of 7 days at 28°C.
Aggelopoulos et al.37 also reported similar findings. A study performed by Araújo et al.38 also reported that use of S. cerevisiae in fermentation would help to increase in protein contents. Correia et al.34 reported that Saccharomyces cerevisiae had significantly increased the crude protein of pineapple waste from 6.4–16%. Hassaan et al.39 prepared soybean meal using S. cerevisiae to enhance protein contents and also supported our results. After 96 hours of incubation, protein amount was found to be decrease which may be due to proteolysis or more production of nitrogen metabolites during fermentation.
Growth Performance And Feed Efficiency
Lack of significant effect on body weight gain is in consistent with Sartori et al.23 who observed that supplementing yeast in the feed of beef cattle showed non-significant effect on daily weight gain. Titi et al.40 also observed no effect of yeast supplementation on average daily gain in lambs. However, Sunato et al.22 found that addition 25% yeast fermented in total mixed ration of dairy cattle resulted in improved body weight. Other researchers41, 42 observed improved daily weight gain in ruminant animals by the supplementation of yeast. It was also found that supplementation of yeast improved growth performance of calves43. This improvement might be due to the supplementation of yeast which enhanced the fiber digestion and ultimately enhanced feed intake44.
Contray to our findings, Özsoy et al.45 reported that goat kids fed diets containing yeast culture consumed less feed dry matter per kg weight gain than those without supplementation during the experiment. Lima et al.17 also found that Saanen goats had higher average daily gain and feed conversion fed dry yeast compared to control. Panda et al.46 reported lower feed to gain ratio in cross-bred calves fed without supplementation compared to supplemented animals. No differences on feed efficiency in calves fed yeast was in consistent with the findings of other researchers47, 48 which might be attributed to lack of significant effect on feed intake and daily weight gain.
Non-significant results were observed when animals were fed diet containing yeast fermentative biomass. Our findings were in consistent with Prado et al.49 who reported that the replacement of cotton seed meal with yeast as a protein source did not influence nutrients intake in 18 months old heifers. In another study, Cherdthong et al.21 replaced soybean meal with yeast fermentative biomass (0, 33 67 and 100% substitution) and found non-significant effect on the feed intake and digestibility. Similarly, Promkot et al.50 reported that addition of different levels of yeast fermented cassava root (10%, 20% and 30% of dry matter) in concentrate had no effect on the dry matter intake among the treatments. It was shown by Anjum et al.24 that the addition of yeast in the diet of Nili Ravi buffalo had no effect on DMI. However, Crosswhite et al.51 noticed higher feed intake by supplementing diets with fermented citrus pulp. The reason for increased intake might be likeness of animals for yeast fermented citrus pulp due to its specific smell and taste or better palatability of the citrus pulp52.
Our findings were in agreement with Cherdthong et al.21 who reported that replacing soybean meal with yeast fermentative biomass had no effect on the digestibility of nutrients. Similarly, Titi et al.40 reported that replacing SBM with inactive dried yeast in beef cattle had no effect on total digestibility and apparent digestibility of the nutrients. However, Khampa et al.53 showed that replacing concentrate with yeast fermented cassava chip in one-year old male cattle resulted in improved digestibility of nutrients. Similarly, Promkot et al.54 reported that replacing SBM with fermented cassava chip improved crude protein and neutral detergent fiber digestibility in cows (p < 0.05). In another study, Promkot et al.50 showed that by adding 20% yeast fermented cassava root improved the digestibility of neutral detergent fiber. Increase in digestibility might be due to high count of cellulolytic bacteria which resulted in efficient utilization of cellulose and more volatile fatty acids production for energy24. Moallem et al.55 also linked improvement in fiber digestion with addition of yeast in diet to enhancement in the production of cellulolytic bacteria.
Lack of effect of yeast fermentative biomass was in accordance with Mutsvangwa et al.56 who reported that supplementation of yeast in bull's ration resulted in non-significant effect on urinary and fecal nitrogen losses. Lehloenya et al.57 noticed that supplementation of yeast culture in steers had non-significant effect on nitrogen balance. Bueno et al.58 also reported similar findings regarding the effect of yeast fermented product on nitrogen balance. However, Sawsan et al.59 observed that supplementation of yeast in the diet of lambs significantly increased the nitrogen balance as compared to non-supplemented group. Cole et al.60 reported that lambs had higher nitrogen balance raised on ration supplemented with yeast culture. The higher nitrogen balance may be due to higher production of microbial protein synthesis as a result of yeast culture61.
Blood Metabolites And Hematological Index
Lack of effect on blood glucose was in consistent with Promkot et al.54 who showed that adding yeast fermented cassava chip in the diet of cows had no effect on blood glucose level. Similarly, Sunato et al.22 reported that adding yeast fermented ethanol waste (0, 25, 35 and 45% of dry matter) in the total mixed ration of the dairy cattle had no effect on blood glucose. However, Dehghan-Banadaky et al.62 found that dairy cow supplemented with live yeast had high blood glucose compared to control group (P < 0.05). In similar study, Dolezal et al.26 reported that adding yeast culture in the diet of Holstein cow increased blood glucose. The probable reason for this might be that adding glycerol enriched yeast in the diet of animals resulted in increase in plasma glucose concentration63.
Our findings on BUN was in agreement with Sunato et al.22 who pointed out that adding yeast fermented ethanol waste in dairy cattle had no effect on BUN. Similarly, Cherdthong et al.21 showed that replacing SBM with yeast biomass had no effect on concentration of BUN. Contrary to this, Dehghan-Banadaky et al.62 reported that adding live yeast in the diet of dairy cow lowered BUN compared to the control group (P < 0.05). Addition of yeast cell wall to dairy cow resulted in lower BUN concentration probably because of the better utilization of NH3-N and better stimulation for ruminal microbial protein synthesis64.
A non-signficant effect was observed on hematological index was non in line with Ghazanfar et al.25 who showed that yeast supplementation in the diet of dairy heifers increased the counts of red blood cells (RBCs) and white blood cells (WBCs) and improved the level of hemoglobin. Similarly, Osita et al.27 reported that diet containing yeast resulted in increase in packed cell volume (PCV), hemoglobin concentration and count of the RBCs and WBCs in African dwarf sheep. The erythrocyte, hematocrit and hemoglobin indices were superior in rabbit supplemented with yeast as compared to control group65.