Effects of Dietary Supplementation of Dried Distillers Grain with Solubles (DDGS) and Yucca (Yucca schidigera) on Broiler Performance, Carcass Traits, Intestinal Viscosity and Marketing

INTRODUCTION

Dried distillers grain with solubles (DDGS) is a commercial residual by-product of ethanol industry from grains (corn, wheat, sorghum etc.). Due to high nutrient content (protein 28-30%), it can be used as an alternative feed source especially in poultry and other domestic animals (20, 23, 31). As a feed component, there are some studies focused on the effectiveness of DDGS on broiler diets (4, 13, 36, 41, 42, 46). However, the inclusion ratio of DDGS and their reported effects on performance and carcass traits are different. For example, Dale and Batal (8) reported that 18% DDGS ratio in diet had a negative impact on performance, while according to Lumpkins et al. (23) the same ratio can be accepted for grower and finisher diets without any negative effect on broiler performance. Wang et al. (42) reported that 15% supplementation of DDGS to diet did not negatively effect on performance, however, 30% of DDGS in diet reduced the weight gain and feed conversation ratio (FCR) in broilers compared to broilers fed without DDGS. Previous reports revealed that the use of DDGS up to 15-20% in broiler diets recommended without negative effect on performance and carcass traits (35, 46, 42). However, the level of 30% and over could be accepted as critical ratio in diet due to mostly negative impacts on performance and/or carcass traits (43). Some researchers argued that high temperature applications damaged the lysine amino acid during ethanol production from cereals and this condition lead to negative effects (29). However, if the stated problem is eliminated, high levels of DDGS in poultry diets could be incorporated as an economical product. Therefore, some studies suggested that various herbal extracts or the enzyme supplementation to diets based on DDGS may prevent some of the negative effects observed in broilers (33).

Y. shidigera is a natural, nontoxic product and easy to available to use and a source of saponin, which contains 9-10% active steroid saponin (11). Kutlu et al. (19) reported that the use of yucca on broiler diets improved the live weight gain and FCR. Similarly, positive effect on FCR was reported in quail (12). There is no study about yucca and DDGS usage together and effectiveness in broilers. Therefore, the aim of present study was to determine the effect of DDGS and Y. shidigera on broiler performance, intestinal viscosity, bacterial count and, to decide marketing type (whole sale or as parts) of carcasses according to financial reflections of treatments.

MATERIAL and METHODS

Animals and Diets

A total of 360 Ross Big6 male chicks were obtained from a local commercial hatchery and they were grown until 21 days of age without any treatment. Feeds obtained from a commercial company. DDGS used in the experiment were imported from USA by the distributor. Chicks were individually weighed and allocated to four groups at 21 days-old with six replicate each of 15 chicks (15 chicks x 6 replicates = 90 chicks per group). Maizewheat-soybean meal based diets were utilized and all of them were formulated using linear programming to be isoenergetic, isonitrogenic. The basal diet was formulated to meet nutrient requirements (26) for 21 to 42 d. Experimental groups were as follows; 1: control group (C, basal diet), 2: DDGS (30%) group, 3: C+Y group (120 mg/kg, Yucca schidigera, Ekomix Yucca, Ekol Feed Additive Ltd., Istanbul). and 4: DDGS (30%) + Y group (120 mg/kg). Small amounts of the basal diet were first mixed with the respective amounts of yucca powder as a small batch, and then with a larger amount of the diets until the total amount of the respective diets were homogeneously mixed. The experimental diets used in this study are given in Table 1. Feed and water were provided ad libitum. The experiment was performed between 21 to 42 days of age (3 weeks). Chicks were housed on a 1.5m x 1.5 m sized wire separated floor pens covered with dry wood shavings litter. Lighting schedule was 23 h light and 1 h dark throughout the experiment. Each pen contained a round feeder and waterer.

Data Collection

The body weight (BW) as individually and feed consumption (FC) by pen bases were obtained at 42 days. Feed conversion ratio (FCR) and body weight gain were calculated for 21 to 42 days. Mortality was recorded daily when occurred and considered for feed consumption.

For carcass and internal organ traits evaluation, 12 broilers (which were represented group mean live weight) in each group were slaughtered by cervical dislocation at the 42 d. The feathers were plucked, and the carcasses were eviscerated by hand. The carcass, liver, proventriculus, empty gizzard, heart, kidney, empty intestine (large+small intestine) weights were recorded. Individually and part yields were obtained as part weight: carcass weight× 100. Cold carcass weight was recorded after the carcasses had been stored at +4°C for 24 h.

Determination of Intestinal pH and Viscosity

The pH value of the duodenal and ileal samples was determined with a pH meter (Hanna Instruments-8413) and measured using a direct probe by thrusting the probe into the duodenal content. The duodenum (pancreatic loop) was carefully excised. Several eppendorf tubes were filled from each samples, labeled and centrifuged (1500 rpm for 5 min). The supernatant was withdrawn and the viscosity of a 0.5 ml aliquot measured using a Brookfield Digital Viscometer (Model DV- II+PRO, Brookfield Engineering Laboratories, Stoughton, MA) maintained at 40°C.

Determination of Microbial Counts

One g of the digesta samples in the ileum the birds were sampled from 12 animals per each group and diluted with 1 ml serum physiologic (0.85% NaCl), homogenized for 3 minutes. Then the diluted ileal samples were inoculated into different media. Sheep blood agar (Merck, Turkey) was used to determine Gram positive microorganisms, and Eosine methylene blue agar (EMB, MAST Diagnostic, UK) was used to identify E.coli. Then inoculates were incubated at 37°C for 24 h. Following the incubation, colonies were counted and amount of the bacteria in the samples were determined quantitatively. The microbial counts were determined as colony-forming units (CFU) per gram of samples as E. coli, Klebsiella spp. Staphylococcus spp. Enterococcus spp. Total Gr negative and Total Gr positive were determined.

Economic Analysis

In economic analysis, the production cost (feed, chick, labour, energy etc.) was calculated, carcass weight, percentage of yield (%) and 4 carcass parts (breast, leg quarter, wing and neck) of slaughtered 12 broilers per group (a total 48 broilers) were determined. Two different marketing types (whole sale or sale as parts) and profits were analyzed. The price of control group’s diet was 1.228 TL/kg; 30% DDGS groups was 1.124 TL/kg; control + Y group’s was 1.235 TL/kg and 30% DDGS + Y group’s was 1.131 TL/kg. Whole sale price of chicks was 5 TL/kg; price of breast 6 TL/kg; thigh 5.5 TL/kg; wing 8 TL/kg and neck 0.5 TL/kg. Besides, cutting cost (labour, energy etc.) was accepted as 0.1 TL per kg of carcass.

Statistical Analysis

Data were subjected to ANOVA using General Linear Models of SPSS (34). The model included type of dietary DDGS and Yucca was presented. Pen means served as the experimental unit for statistical analysis. Differences among means were tested using Duncan’s multiple-range tests with a 5% level of probability was used. Paired sample t-test was used in comparing profits of two different marketing types.

Table 1. Composition of diets used in the study*

Effects of Dietary Supplementation of Dried Distillers Grain with Solubles (DDGS) and Yucca (Yucca schidigera) on Broiler Performance, Carcass Traits, Intestinal Viscosity and Marketing - Image 1

RESULTS

The performance parameters, carcass parts and financial impact of different marketing ways of broilers are given in Table 2.

Performance parameters such as BW, BWG, FC, FCR and mortality rate were not affected by the treatments (P>0.05). Although not significant, the highest dressing yield was determined in DDGS group (2nd) and a slight decrease was determined in 4rd group Percentage of internal organs to live weight were not affected by the treatments (P>0.05).

The percentage of carcass parts were not differs among the groups. Only the percentage of leg quarter in the 4th group was slightly less than other groups.

According to economic results, the production cost was minimum in the 2nd group and profit between different marketing types (wholesale or as cuts) was significantly different (P<0.05).

There were no significant effect of treatments on intestinal viscosity and duodenal and ileal pH values (Table 3).

The effects of treatments on intestine microorganism numbers (log transformed data) were given in Table 4. The yucca supplementation decreased E.coli counts compared to control group (P<0.05); DDGS and DDGS+Y groups were similar with C and C+Y groups. The Klebsiella spp. counts were not statistically different among the groups (P>0.05). In the C+Y and DDGS+Y groups Staphylococcus counts were higher than those of C and DDGS groups (P<0.01). In the C group the Enterococcus and total gram negative microorganisms counts were higher than those of other groups (P<0.01). In the DDGS group total gram positive microorganism count was lower than those of other groups (P<0.01).

DISCUSSION

According to authors' knowledge, there is no study on the use of DDGS and Yucca together in broiler diets. Thus, the data obtained from this study is the first attempt to use of DDGS and Yucca in broiler diets. So we discussed the results by DDGS cited references or yucca cited references in present study.

Performance

In the study, broiler performance traits were not significantly affected by the DDGS and yucca supplementation. It is reported that inclusion of 25% (39) and 30% DDGS (44) to the broiler diets did not have any negative impact on performance parameters. Youssef et al (46) reported that 10-15% DDGS as a protein source could be include without negative effects on broilers’ weight gain and feed intake, however especially FCR values decline. Kaya and Sahin (15) reported that, DDGS supplementation to the broiler diets up to 15% improved performance parameters (BW, BWG, FC and FCR). Mortality rate was not affected in the current experiment. Similar results were obtained by Wang et al. (42,44) and Youssef et al. (46), that they had used the diets with 30% and 15% DDGS respectively.

Table 2. Effects of treatments on performance and marketing of broilers

Table 3. Effects of treatments on viscosity values

Table 4. The effects of treatments on intestine microorganism counts (log transformed data)

Ahmed et al. (2) reported that yucca extract is a safe product for broilers and yielded better weight gain. The yucca supplementation to corn and DDGS based diets did not affect performance traits in this study. Similarly, yucca extract supplementation to diets in broilers (7,45), in quail (9,11) and laying hens (18) did not affect positively on the body weight, feed intake and feed efficiency and carcass yields of quail (9). On the other hand, Kutlu et al. (19) reported that yucca incorporation to diets improved broiler performance parameters. Also, Begum et al. (5) noted that the addition of 100 mg/kg yucca and caprylic acid to the diet improved growth performance and reduced mortality rate in broiler chickens.

Carcass quality

In the current study, carcass yield, carcass parts, internal organ weights and their ratios to cold carcass or live weight were not influenced by the treatments. The findings of Kaya and Sahin (15) about the use of DDGS are similar with present study. Similar findings were observed by the Lumpkins et al. (23) who reported that the use of 18% DDGS in broiler diets didn’t reduce the carcass yield. In contrast to present experiment results, Wang et al. (43), Wang et al. (44) and Min et al. (24) reported that 30 % DDGS levels caused a decrease in carcass yield of broilers. Regarding to internal organ weights, Loar et al. (21) reported that increasing from 8 to 25% DDGS inclusion levels during the grower phase resulted in a linear decrease in liver relative weight. Wang et al. (41) reported that inclusion of 15 or 25% DDGS decreased the dressing percentage, and chickens fed the diet with 25% DDGS was characterized by lower breast weight. Konca et al. (17) reported that 30% DDGS inclusion to diet did not significantly effect on carcass traits in quail. Youssef et al. (46) reported that 10-15% DDGS as a protein source could be include without negative effects on carcass yield, liver weight and heart weight.

On the other hand, some previous reports claimed that inconsistent results related to carcass and parts ratio. Wang et al. (42) noted that DDGS ratio in diets more than 25% and Lukaszewicz and Kowalczyk (22) 15% decreased carcass and breast meat yield in broilers. In contrast to these results, Schilling et al. (32) reported that 18-24 % DDGS incorporation to broiler diets increased breast meat ratio compared to control group.

However, Wang et al. (44) reported that 30% DDGS declined the dressing percentage, breast meat yield and leg quarter. Adamski et al. (1) reported that, 30% inclusion of DDGS did not negatively affect the body weight, slaughter yield, breast, leg, abdominal fat, neck and wings weights in male ducks. Therefore, Adamski et al. (1) suggested that the use of DDGS up to 30% in Pekin ducks, parallel with present study.

Yucca supplementation to control and DDGS diets were not affected carcass and internal organ weights and ratios. In contrast to current results, Sahoo et al. (28) reported that, the breast meat yield of Yucca group (32.23%) was significantly higher than control group (30.33%).

Marketing

The use of DDGS in broiler diets and its impact on performance is important for reducing the feed cost. In this study, the percentage of carcass parts were not influenced by the treatments. However, according to economic results, the production cost was minimum and profit maximum in the DDGS and DDGS+Y groups. In fact that, main effect on reducing the production costs was due to DDGS. So, without negative effects, maximum level of DDGS in diets reflects on production costs and profit. In the present experiment, yucca supplementation did not affect production cost and profit. On the other hand, Sahoo et al. (28) reported that, a profit of 43.68% was received by usage of Yucca supplementation in the diet on live weight basis.

Intestinal viscosity and microorganism counts

In the present study, there were no any significant effect of treatments on intestinal viscosity, pH values and Klebsiella spp. counts. However, the yucca supplementation were decreased E.coli counts. Similar findings also reported that Wang and Kim (40), the addition of 120 mg/kg Yucca extract reduced the proliferation of E. coli. According to the Begum et al. (5) the addition of 100 mg/kg yucca and caprylic acid to the diet reduced caecal E. coli counts compared with those fed the control diet in broiler chickens. Alfaro et al. (3) suggested that there might be a beneficial, synergistic effect between the coccidiosis vaccine and the Y. schidigera extract.

In present study, the Staphylococcus were increased in control and DDGS based diets. Also, the Enterococcus and total gram negative microorganism counts were lower in diets containing Yucca and DDGS than control group. Y. schidigera supplements can indeed influence the growth and metabolism of microbial populations, even in artificial fermentation systems which eliminate any indirect effects that may be exerted via a host animal (6,10,27,37,38). In several studies (3,25,30,47) the addition of Yucca extract to diets positively affected the intestinal mucosal histology. Kadsunuma et al. (14) obtained that Y. schidigera extract and saponins provide useful and basic information for analyzing the effects on the constitution of microflora in intestinal tract. They also said that these results show that the principal responsible agent for antibacterial activity exhibited by the Y. schidigera extract may be the saponins.

CONCLUSION

In conclusion, supplementation of yucca to control and DDGS based rations was not improve the carcass traits and DDGS could be used in broiler diets up to 30% without negative effect on performance, carcass yield and profit.

ACKNOWLEDGEMENTS

We thank ERUTAM for poultry breeding facility in the experiment and thank Agr. Tec. Mustafa Ogretmen, Kuddusi Kuru and Reha Yildiz for technical assistant.

This article was originally published in Journal of Poultry Research 12(1): 5-11, 2015 Print ISSN:1302-3209 - Online ISSN:2147-9003. This is an Open Access article licensed under Creative Commons Attribution 4.0 International License.

REFERENCES

1. Adamski, MP., Kowalczyk, AM., Lukaszewicz, ET., Korzeniowska, M. 2011. Effects of sex and inclusion of dried distillers grains with solubles on slaughter yield and meat characteristics of Pekin ducks. British Poultry Science, 52(6): 742-749.

2. Ahmed, D., Anjum, F., Rizvi, A., Asi, E. 1999. Effect of Yucca schidigera Extract (Norponin-S) on Health of Broiler Chickens. Pakistan Journal of Biological Sciences, 2(1): 484-486.

3. Alfaro, DM., Silva, AVF., Borges, SA., Maiorka, FA., Vargas, S., Santin, E. 2007. Use of Yucca schidigera extract in broiler diets and its effects on performance results obtained with different coccidiosis control methods. The Journal of Applied Poultry Research, 16(2): 248-254.

4. Applegate, TJ., Troche, C., Jiang, Z., Johnson, T. 2009. The nutritional value of high-protein corn distillers dried grains for broiler chickens and its effect on nutrient excretion. Poultry Science, 88(2): 354-359.

5. Begum, M., Hossain, MM., Kim, IH. 2015. Effects of caprylic acid and Yucca schidigera extract on growth performance, relative organ weight, breast meat quality, haematological characteristics and caecal microbial shedding in mixed sex Ross 308 broiler chickens. Veterinarni Medicina, 60(11): 635-643.

6. Coodall, SR., Brady, P., Horton, D., Beckner, B. 1982. Steam flaked vetsus high moisture corn rations with and without sarsaponin for finishing steers. Western Section American Society of Animal Science, 33(1): 45-48.

7. Çabuk, M., Alçiçek, A., Bozkurt, M., Akkan, S. 2004. Effect of yucca shidigera and natural zeolite on broiler performance. International Journal of Poultry Science, 3(10): 651-654.

8. Dale, N., Batal, A. 2003. Nutritional value of distillers dried grains and solubles for poultry. In 19th Annual Carolina Nutrition Conf. Research Triangle Park (NC) EUA.

9. Erdogan, Z., Erdogan, S., Kaya, S. 2001. Yucca ekstraktinin bildircinlarda besi performansi ile bazi biyokimyasal ve hematolojik parametreleri üzerine etkisi. Ankara Üniversitesi Veteriner Fakültesi Dergisi, 48(1): 231-236.

10. Grobner, MA., Johnson, DE., Goodall, SR., Benz, DA. 1982. Sarsaponin effects on in vitro continuous flow fermentation of a high grain diet. Journal of Animal Science, 55(1): 491.

11. Güçlü, BK. 2003. Bildircin rasyonlarina katilan Yucca schidigera ekstraktinin yumurta verimi ve yumurta kalitesi ile bazi kan parametrelerine etkisi. Turkish Journal of Veterinary Animal Science, 27(1): 567-574.

12. Güçlü, BK., Iscan, KM. 2004. Bildircin rasyonlarina katilan Yucca schidigera tozunun besi performansina etkisi. Erciyes Üniversitesi Veteriner Fakültesi Dergisi, 1(1): 15-20.

13. Hassan, SM., Al Aqil, AA. 2015. Effect of adding different dietary levels of distillers dried grains with solubles (DDGS) on productive performance of broiler chicks. International Journal of Poultry Science, 14(1): 13-18.

14. Katsunuma, Y., Nakamura, Y., Toyoda, A., Minato, H. 2000. Effect of Yucca shidigera extract and saponins on growth of bacteria isolated from animal intestinal tract. Animal Science Journal, 71(2): 164- 170.

15. Kaya, Ö., Sahin, T. 2013. Effects of different levels distillers dried grains with solubles on growth performance, carcass quality and some blood parameters in broilers. Kafkas Üniversitesi Veteriner Fakültesi Dergisi, 19(1): 161-166.

16. Kleinschmit, DH., Schingoethe, DJ., Kalscheur, KF., Hippen, AR. 2006. Evaluation of various sources of corn dried distillers grains plus solubles for lactating dairy cattle. Journal of Dairy Science, 89(12): 4784– 4794.

17. Konca, Y., Kirkpinar, F., Mert, S., 2011. Effects of corn distillers dried grain with solubles (DDGS) on carcass, meat quality and intestinal organ traits in Japanese quail. Scientific Papers seria D Animal science, pp. 39-44.

18. Kutlu, HR., Görgülü, M., Ünsal, I. 2001. Effects of dietary Yucca schidigera powder on performance and egg cholesterol content of laying hens. Journal of Applied Animal Research, 20(1): 49-56.

19. Kutlu, HR., Ünsal, I., Karaman, M., Görgülü, M., Yurtseven, S., Baykal L. 1999. Etlik piliçlerin performansi üzerine Yucca schidigera Tozu (DK Toz 35)’nun etkisi. Yem Magazin, 21(1): 29-32.

20. Lim, C., Yildirim Aksoy, M. 2008. Distillers dried grains with solubles as an alternative protein source in fish feeds. 8th International Symposium on Tilapia in Aquaculture, pp. 12-14.

21. Loar, RE., Moritz, JS., Donaldson, JR., Corzo, A. 2010. Effects of feeding distillers dried grains with solubles to broilers from 0 to 28 days posthatch on broiler performance, feed manufacturing efficiency, and selected intestinal characteristics. Poultry Science, 89(10): 2242-50.

22. Lukaszewicz, E., Kowalczyk, A. 2014. Slaughter yield and breast meat quality of chicken broilers in relation to sex and level of dietary maize distillers dried grains with solubles (DDGS). Revue de Médicine Véterinaire, 165(5-6): 176-182.

23. Lumpkins, BS., Batal, AB., Dale, NM. 2004. Evaluation of distillers dried grains with solubles as a feed ingredient for broilers, Poultry Science, 83(11):1891-1896.

24. Min, YN., Hancock, A., Yan, F., Lu, C., Coto, C., Karimi, A., Park, JH., Liu, FZ., Waldroup, PW. 2010. Use of combinations of canola meal and distillers dried grains with solubles in broiler starter diets. Journal of Applied Poultry Research, 18(4): 725-733.

25. Morales-Lopez, R., Auclair, E., Garcia, F., EsteveGarcia, E., Brufau, J. 2009. Use of yeast cell walls; 1, 3/1,6-glucans; and mannoproteins in broiler chicken diets. Poultry Science, 88(3): 601–607.

26. NRC, National Research Council. 1994. Nutrient Requirements of Poultry. 9th rev. ed. National Academy Press, Washington, DC

27. Peestock, LA. 1979. An investigation into the application of Yucca schidigera extracts to biological waste treatments (Doctoral dissertation, M. Sc. Thesis, Miami University, Oxford, OH).

28. Sahoo, SP., Kaur, D., Sethi, APS., Sharma, A., Chandra, M. 2015. Evaluation of Yucca schidigera extract as feed additive on performance of broiler chicks in winter season. Veterinary World, 8(4): 556- 560.

29. Salim, HM., Kruk, ZA., Lee, BD. 2010. Nutritive value of corn distillers dried grains with solubles as an ingredient of poultry diets: A review. World's Poultry Science Journal, 66(03): 411-432.

30. Santin, E., Maiorka, A., Macari, M. 2001. Performance and intestinal mucosa development of broilers chickens fed diets containing Saccharomyces cerevisiaes cell wall. The Journal of Applied Poultry Research, 10(3): 236–244.

31. Schauer, CS., Stamm MM., Maddock TD., Berg PB. 2008. Feeding of DDGS in lamb rations. Sheep & Goat Research Journal, 23(1): 15-19.

32. Schilling, MW., Battula, V., Loar, RE., Jackson, V., Kin, S., Corzo, A. 2010. Dietary inclusion level effects of distillers dried grains with solubles on broiler meat quality. Poultry Science, 89(4):752-760.

33. Shalash, SMM., El-Wafa, SA., Hassan, RA., Ramadan, NA., Mohamed, MS., El-Gabry, HE. 2010. Evaluation of distillers dried grains with solubles as feed ingredient in laying hen diets. International Journal of Poultry Science, 9(1): 537-545.

34. SPSS, Software, 1996. Changes and Enhancements through Release 6.11, Cary, NC: SAS Institute Inc.

35. Swiatkiewicz, S., Koreleski, J. 2008. The use of distillers dried grains with solubles (DDGS) in poultry nutrition. World's Poultry Science, 64 (02): 257-265.

36. Tracker, PA., Widyaratne, GP. 2007. Nutritional value of diets containing graded levels of wheat distillers grains with solubles fed to broiler chicks. Journal of the Science of Food and Agriculture, 87(7): 1386-1390.

37. Valdez, FR., Bush, LJ., Goetsch, AL., Owens, FN. 1986. Effect of steroidal saponins on ruminal fermentation and on production of lactating dairy cows. Journal of Dairy Science, 69(6): 1568–1575.

38. Van Nevel, CJ., Demeyer, DI. 1990. Effect of antibiotics, a deaminase inhibitor and sarsaponin on nitrogen metabolism of rumen contents in vitro. Animal feed science and technology, 31(3): 323-348.

39. Waldroup, PW., Owen, JA., Ramsey, BE., Whelchel, DL. 1981. The use of high levels of distillers dried grains plus solubles in broiler diets. Poultry Science, 60(7): 1479-1484.

40. Wang, JP., Kim, IH. 2011. Effect of caprylic acid and Yucca schidigera extract on production performance, egg quality, blood characteristics, and excreta microflora in laying hens. British poultry science, 52(6): 711-717.

41. Wang, Z., Cerrate, S., Coto, C., Yan, F., Waldroup, PW. 2007a. Effect of rapid and multiple changes in level of distillers dried grain with solubles (DDGS) in broiler diets on performance and carcass characteristics. International Journal of Poultry Science, 6(10): 725-731.

42. Wang, Z., Cerrate, S., Coto, C., Yan, F., Waldroup, PW. 2007b. Use of constant or increasing levels of distellers dried grains with solubles (DDGS) in broiler diets. International Journal of Poultry Science, 6(7): 501-507.

43. Wang, Z., Cerrate, S., Coto, C., Yan, F., Waldroup, PW. 2007c. Utilization of Distillers Dried Grains with Solubles (DDGS) in Broiler Diets Using a Standardized Nutrient Matrix. Poultry Science, 6(7): 470-477.

44. Wang, Z., Cerrate, S., Coto, C., Yan, F., Waldroup, PW. 2008. Evaluation of high levels of distellers dried grains with solubles (DDGS) in broiler diets. International Journal of Poultry Science, 7(10): 990- 996.

45. Yeo, J., Kim, K. 1997. Effect of feeding diets containing an antibiotic, a probiotic, or yucca extract on growth and intestinal urease activity in broiler chicks. Poultry Science, 76(2): 381-385.

46. Youssef, IMI., Westfahl, C., Sünder, A., Liebert, F., Kamphues, J. 2008. Evaluation of dried distillers' grains with solubles (DDGS) as a protein source for broilers. Archives of Animal Nutrition, 62(5): 404-414.

47. Zhang, AW., Lee, BD., Lee, SK., Lee, KW., An, GH., Song, KB., Lee, CH. 2005. Effects of yeast (Saccharomyces cerevisiae) cell components on growth performance, meat quality, and ileal mucosa development of broilers chicks. Poultry Science, 84(7): 1015–1021.