Custom services
text in 
English (pdf)
Article in xml format
Article references
Send this article by e-mail
Cited by SciELO 
Similars in
SciELO 
Permalink
INTRODUCTION
Currently, the global energy crisis and the increase in the price of crude oil have led human beings to seek new means for obtaining alternative and less polluting energies that gradually replace oil as a non-renewable resource. With this purpose, biofuels emerged (Aristizabal 2016 and Jones and Mayfield 2016).
Biofuels represent the final product of the use of crops like sugar cane, maize, soy bean, sunflower, r a p e se e d a n d o t h e rs. T h i s t e c h n o l o g y, d e sp i t e contributing to environmental decontamination, has brought a new source of volatility in the markets of basic agricultural products, affecting the food security of many countries, especially those that are importers of these foods (Romero 2013). This industry generates a large amount of byproducts, and dried distillery grains with solubles (DDGS) are among them, which availability, nutritional value and costs are an opportunity for animal feed.
DDGS are used in the feeding of all types of animals, whether they are ruminants or monogastric animals, mainly pigs and birds (Adedokun et al. 2015 and Wu et al. 2016). However, there is still limited knowledge about its use in rabbits, since rabbit breeding studies are scarce.
The objective of this review is to collect information related to the nutritional composition of DDGS from different sources (maize, sorghum, wheat and barley), as well as to summarize the research that has been carried out with the use of this byproduct in rabbits.
OBTAINING DDGS
Ethanol can be produced from a cereal or from a combination of different cereals. The most commonly used are maize, in the United States, wheat in Canada, sorghum in certain American states (Kansas) and barley in northern European countries. In Spain, these four cereals have been used indistinctly during the last years. The name of the grain that is used in greater quantity is taken to denominate the resulting by-product. Maize distillery grains, for example, generated in ethanol production plants, receive this denomination because maize is the most used cereal (US Grains Council 2007).
The process of developing DDGS is relatively simple. Grains are milled, moistened and cooked under pressure to gelatinize the starch (occurs between 50 and 70 ºC) and significantly reduce the microbial population of the mixture.
For the complete hydrolysis of the starch polymer, a combination of thermostable amylases, such as α amylase and glucoamylase, is added. Then yeast (Sacharomyces ceriviseae) is included to convert sugars into alcohol (ethanol). Approximately, after 40-72 h of fermentation, ethanol is distilled and the residual mixture is separated into light distillate and coarse solids. Maize oil is extracted from the light distillate and water is removed by centrifugation to produce condensed distillers solubles (CDS). Finally, 75 to 100 % of the CDS are mixed with the fraction of humid grains and dried using rotary dryers to produce DDGS (Rosentrater et al. 2012).
Among the by-products of dry-mill ethanol plants, dried distillery grains (DDGS), distillery dried solubles (DDS) and dried distillers' grains with solubles or DDGS are included.
GLOBAL PRODUCTION OF DDGS
The United States is the world's largest producer of ethanol and, consequently, of DDGS. Its productions have increased in recent years from 2.7 million tons in 2000 to 40 million tons in 2015, with forecasts for 2018 of 44 million (Jensen et al. 2013). For the same year, globally, a production of approximately 57 million tons of DDGS is projected (table 1) (Jensen et al. 2013).
Regarding the use in animal production, the largest consumers of DDGS in the United States are ruminants, with an intake of 80 % of the total DDGS produced, followed by pigs that already reach 12 %, while poultry industry uses around 8 % (table 2). There is little evidence of significant amounts being used in aquaculture.
CHEMICAL COMPOSITION OF DDGS OF DIFFERENT GRAINS
Processing conditions before grain fermentation for the production of ethanol may affect, to a large extent, the quantity, quality and nutritional composition of the different by-products. Likewise, due to the variation of nutrient composition of the grains that are used to produce ethanol varies, the nutrient composition of resulting distillery grains also changes. Table 3 shows the composition of nutrients (under dry basis) of DDGS from different sources.
Sources: Stein et al. (2006), Widyaratne y Zijlstra (2007), Depenbusch et al. (2009), Avelar et al. (2010), Cozannet et al. (2010), Martínez (2011), Alagón (2012), FEDNA (2012), Alagón (2013) and Abdelqader and Oba (2013).
In general, DDGS from different sources have a high content of crude protein (28.2-37.3 %), which is related to starch extraction during fermentation, by tripling the proportion of protein and other nutrients (de Blas and Mateos 2010). DDGS of wheat show the highest value. In relation to sulfur amino acids, methionine and cystine have a high contribution, which allows achieving a good balance of these nutrients. As for lysine, grains of barley, maize, wheat and sorghum have low content (from 2.7 to 3.6 % of PB) (FEDNA 2012). Therefore, protein levels of their DDGS are also low in lysine (from 0.91 to 3.0 % PB).
Total ash content is among the permissible values and varies from 4.5- 5.9 %. The high phosphorus content is highlighted, higher in wheat DDGS, which is associated with the normal variation of phosphorus in the grain (Widyaratne and Zijlstra 2007). According to Pedersen et al. (2007), total digestibility of phosphorus in DDGS is 59 %, while the available phosphorus reaches values between 62 and 100 %.
This improvement in the availability of P is attributed to the extracellular phytases that release yeasts during the fermentation process and that hydrolyze the phytic acid (Morales and Valdivié 2011). All this represents a nutritional advantage for rabbits, which allows to reduce the use of inorganic phosphorus, when using DDGS in diets.
Regarding digestible energy, DDGS of barley and sorghum are less energetic than DDGS of maize and wheat. Their values range from 11.30 - 15.8 MJ kg DM-1 and are in the recommended range for rabbits, according to Machado et al. (2011). These figures depend, to a large extent, on the amount of solubles added and the lipid content, so their determination is basic when included in diets for monogastric animals (Martínez 2011).
With respect to fiber, contents of NDF, ADF and hemicelluloses ranged from 34.0-60.1 %; 13.623.8 % and from 21.26-27.25 %, respectively. All were superior in the DDGS of barley regarding DDGS of maize and wheat, which also corresponds to the fiber composition of these cereals (de Blas et al. 2010). Also, DDGS of different sources showed high values of soluble fiber in neutral detergent (NDSF), from 20.26 - 21.73 %. This component is of great interest, since it is attributed functional properties in the intestinal health of weaned rabbits (Alagón 2012).
This review do not show values of the composition of vitamins of DDGS. It is known that DDGS, like almost all foods generated in fermentation processes, where yeasts participate, are rich in water-soluble vitamins. This is due to the fact that live yeasts, during the fermentation process, release their enzymes and B complex vitamins in the substrate (Morales and Valdivié 2011), which contributes to the richness of water-soluble vitamins in DDGS.
USE OF DRIED DISTILLERS GRAINS WITH SOLUBLE IN RABBIT FEED
Very little research has been carried out to evaluate the nutritional value of DDGS in rabbits. Studies have been carried out on growth-fattening rabbits on the chemical characterization of DDGS from different sources (Alagón 2012), productive performance (Vázquez et al. 2011 and Chelminska and Kowalska 2013), digestive and physiological studies (Villamide et al. 1989, Petkova et al. 2011, Alagón et al. 2012 and Vázquez et al. 2016), as well as carcass yield (Vázquez 2014 and Alagón et al. 2015). Trials have also been aimed at the study of the partial or total substitution of ingredients of the diet for DDGS (Bernal et al. 2010 and Soliman et al. 2010) and the analysis of the combination of this by-product with different enzymes (Liñán 2012 and Khattab et al. 2014).
A) STUDIES ON CHEMICAL CHARACTERIZATION
Alagón (2012) conducted a study of chemical characterization and determination of the nutritional value of DDGS from barley, maize and wheat in growing rabbits. DDGS of wheat and maize obtained higher CP contents (35.32 and 30.31 % DM, respectively) while those of maize were richer in crude fat (14.13 % DM) and those of barley had the highest content of NDF (40.10 % DM) and ADF (12.85 % DM). Regarding NDSF, contents were considerably high (21 % DM on average) and did not differ among the different types of DDGS.
Saturated fatty acids (SFA) were found in greater proportion in the DDGS of barley and wheat, while the latter had, in addition, higher concentration of polyunsaturated (PUFA), and those of maize with more monounsaturated (MUFA). Digestibilities of dry matter (DM), organic matter (OM) and gross energy (GE) increased with the inclusion of DDGS of maize (59.65, 59.98 and 60.62 %) and wheat (60.03, 60.47 and 60.87%), while the inclusion of DDGS of barley only increased the digestibility of the FDA (13.38%). CP digestibility was not affected by the inclusion of DDGS. Values of amino acid digestibility for lysine, threonine and methionine were higher in feeds with DDGS of maize (0.94, 0.83 and 0.34%) and wheat (0.97, 83 and 0.33%), with respect to those that included DDGS of barley (0.87, 0.72 and 0.32%). In this study of Alagón (2012), values of 11.9, 14.7 and 15.7 MJ of DE/kg DM were obtained, and of 168, 221 and 263 g of DP/kg of DM (digestible protein per kg of DM) for DDGS of barley, maize and wheat, respectively.
This study indicates that, for rabbits, DDGS may be considered good protein sources, especially those of wheat and maize. Likewise, due to the high content of NDF and NDSF, as well as due to the increase in their digestibility, DDGS may also be evaluated as fiber sources, which is an aspect that is of interest, since functional properties in the intestinal health of rabbits are attributed.
B) STUDIES ON PRODUCTIVE PERFORMANCE
Vázquez et al. (2011) conducted a study to determine the effect of adding 0, 10 or 20 % of DDGS in the productive performance of growing rabbits. These authors found no differences on studied variabilities (initial and final weight, daily gain, food intake and food conversion).
Amani et al. (2012) led an essay to evaluate the nutritional value and the effect of inclusion of 0, 10, 20 or 30 % of DDGS in the feeding of growing rabbits, weaned at 42 d old. In these results, rabbits fed 10, 20 and 30 % of DDGS reduced food intake in 6.0, 6.6 y 7.2 % respectively, compared to rabbits fed control diet. Final weight and daily mean gain did not differ among treatments. Food conversion was significantly better for rabbits fed 30 % of DDGS (1.89), compared to those fed 0 % and 20 % of DDGS (1.97 y 1.94) and to control group (2.09). These results show that rabbits that ingested 30 % of DDGS needed less amount of food per kilogram of weight gain. The authors suggested this inclusion level on the diet of growing rabbits because they did not find differences in the final weight of animals.
In another study by Vázquez et al. (2013), the effect of including 0, 10, 20 or 30 % of DDGS in diets of sorghum-soybean meal for fattening rabbits was determined. These authors used 56 rabbits, 40 d of age and average liveweight of 752 g. As a result, they found no differences in animal weight or feed intake. Rabbits that ingested 20% of DDGS achieved the highest liveweight gain, without significantly differing from those fed diets with inclusion levels of 0 and 10 %, and those fed with 30% of DDGS.
Feed conversion was significantly lower in animals that ingested 10 % of DDGS, which only differed from those who ingested 30 % of DDGS. With these results, cited authors recommended the inclusion of DDGS only up to 20 %.Chelminska and Kowalska (2013) observed a decrease in body weight, food intake and weight gain in rabbits fed 10% of inclusion of DDGS on the diet, compared to those who received the control diet and5 % of DDGS. Food conversion also showed differences, and was lower in the group fed 10 % of DDGS. In correspondence with these results, studies on meat quality and yield showed lower carcass yield in rabbits that ingested 10 % of DDGS, so the authors suggested the inclusion of up to 5 % of DDGS in the diet of growing rabbits.
Rohloff Junior (2015) evaluated the effect of including 0, 6, 12, 18 and 24 % of DDGS in the productive performance of growing rabbits. By including 24 % of the by-product, animals showed no difference in liveweight or weight gain. However, as the level of DDGS increased, food consumption and food conversion decreased. Although these researches were carried out in different environments and conditions, results indicate that it is possible to include up to 30 % of DDGS in diets of growing rabbits.
C) DIGESTIVE AND PHYSIOLOGICAL STUDIES
Regarding these studies, Villamide et al. (1989), in Spain, compared nutrient digestibility of wheat bran, maize gluten meal and DDGS in hybrid New Zealand x California rabbits. Basal diet contained a low amount of energy (8.37 MJ/kg of dry matter) and a high protein energy relation (25 Kcal of DE/g of digestible protein). Although fiber content of the diet was similar, the energy digestibility and the ADF was higher for rabbits fed DDGS diet (74.0 % and 58.3 %, respectively) compared to rabbits receiving diets containing wheat bran (59.4 % and 9.6%, respectively) and maize gluten meal (65.0 % and 27.7%, respectively).
In addition, rabbits fed DDGS diet had the highest level of protein digestibility (70.1 %) compared to those who received wheat bran (66.6 %) and maize gluten meal (61.4%). These results indicate that DDGS is a suitable ingredient for rabbit diets, providing more energy, ADF and digestible protein than wheat bran and maize gluten meal.
Petkova et al. (2011) evaluated the effect of three fiber sources on biochemical and physiological changes of growing rabbits. These authors used a control treatment, with 30 % of alfalfa hay, a second treatment with 10 % of DDGS of wheat plus 20 % of hay and a third treatment with 15 % DDGS of wheat plus 15 % of wheat straw. Results showed that there was no incidence of digestive disorders in experimental groups.
Alagón et al. (2012) performed a digestibility test with 72 rabbits kept in different environmental temperature conditions to determine coefficients of nutrient digestibility and digestible energy (DE) content, digestible protein (DP) of DDGS and beet pulp. Treatments consisted of a control diet and the substitution of 20% of this diet for DDGS or beet pulp. These authors reported that environmental conditions affected all apparent digestibility coefficients. Animals subjected to heat stress showed significantly lower daily food intake, as well as an increase in apparent digestibility coefficients of the main nutrients (DM, CP, GE, NDF and ADF) in comparison with those that stayed under normal conditions and received the diet independently. Values of digestible energy were less affected by environment, being the DE of 11.6 and 11.7 MJ/kg of DM for DDGS and of 15.0 and 14.2 MJ/kg of DM of beet pulp under heat stress conditions and under normal temperature conditions, respectively.
Mohamed et al. (2013) used maize-soybean diets with 0, 10, 20, 30 or 40 % of DDGS to evaluate nutrient digestibility and productive response of growing rabbits. DDGS were replaced by maize and soybean to maintain constant levels of total lysine (0.35 %). There was no influence of these DDGS levels on weight, gain, intake or feed conversion.
Strychalski et al. (2014) evaluated the use of DDGS of wheat and rapeseed cake and its effect on the physiological changes of the gastrointestinal tract of rabbits. They used four diets: a control group with 5 % of soybean meal, 5 % of rapeseed cake, 5 % of DDGS of wheat and one last treatment with 2.5 % rapeseed cake plus 2.5 % of DDGS of wheat. They did not find differences in the performance of animals. Nutrient digestibility and energy and nitrogen retention were higher in the control group than in rabbits receiving DDGS. In turn, these animals were the ones with the highest weight of the small intestine. The activity of bacterial enzymes of the cecum was similar in all groups. The enzymatic activity of the colon microbiota of rabbits that ingested 2.5 % of rapeseed cake plus 2.5 % of DDGS of wheat had higher effect in the use of the nutrients of the diet regarding those that received 5 % of DDGS of wheat. Results indicated that soybean meal in rabbit diets can be replaced by 5% rapeseed cake and by 2.5 % rapeseed cake, plus 2.5 % of DDGS of wheat.
Rohloff Junior (2015) also evaluated the effect of including 0 and 30 % of DDGS of maize on nutrient digestibility of growing rabbits. This author found high digestibility, in particular for protein (74.10 %) and lipids (81.51 %), as well as high content of digestible protein (21.85 %) and digestible energy (2.979 kcal/kg).
Recently, Vázquez et al. (2016) determined the morphometry of the gastrointestinal tract (GIT) and internal organs in growing rabbits, by including 0, 10, 20 and 30 % of DDGS of maize in the diet. With 30 % of DDGS, these authors obtained the highest weights of full and empty stomach, absolute (93.75 and 33.75 g) as relative (4.54 and 1.58 g) and metabolic (0.31 and 0.11 g g0.75-1). These authors also showed a decrease in the absolute weight of liver with the inclusion of 30 % of this by-product, but these differences disappeared when the metabolic weights were analyzed.
These researches suggest that the use of 20 % of DDGS increases nutrient digestibility of the diet, mainly of CP, ADF, NDF and energy, while the inclusion of up to 30 % of this byproduct does not cause morphometric disorders of the gastrointestinal tract and internal organs of growing rabbits.
DDGS contain oligosaccharides from mannan, from the walls of yeast, which have the potential to improve immunity. Results obtained by these authors can be attributed to the beneficial effect of the oligosaccharides, favoring the development of intestinal villi and improving liveweight gain and absorption efficiency and use of nutrients (Morales 2007).
D) STUDIES ON CARCASS PERFORMANCE
Vázquez (2014) evaluated the quality characteristics of carcasses and meat in rabbits fed 0DDGS (0, 10, 20 or 30 %). He did not find differences in the performance of the carcass nor in the performance of edible viscera (liver, heart, kidneys and spleen). Out of the commercial parts of the carcass, the highest percentages were of hinder limbs and loin. In the sensorial analysis of meat, pleasant smell, pale color and smooth texture were evident. With these results, the author concluded that it is possible to include up to 30% of DDGS in rabbit diets, without changes in the quality of the meat.
E) STUDIES ON PARTIAL OR TOTAL REPLACEMENT DIET INGREDIENTS BY DDGS
Bernal et al. (2010) determined the effect of partially replacing sorghum grain and soybean meal with DDGS in isonitrogenated (17.4 % PC) and isoenergetic diets (11.72 MJ/kg) of growing rabbits. No significant differences were found in the performance of rabbits, so the authors concluded that it is possible to replace 30 % of the sorghum and soy of the diet by DDGS in the feeding of growing rabbits.
Soliman et al. (2010) published their results on the partial replacement of diet protein by DDGS in growing rabbits. For the study, they used six diets with the inclusion of DDGS to replace 10, 20, 30, 40 and 50 % of the protein from the protein source (soybean meal) of the control diet or 6.25, 12.50, 18.75, 25.00 and 31.25 % of the total diet, respectively. They found no negative effects on the productive performance of rabbits fed DDGS, as well as on carcass traits and organoleptic characteristics of meat, regardless of the substitution level, except for the food conversion that was unfavorable with 40 and 50 % substitution. The lowest values of liveweight, weight gain and food conversion were obtained in rabbits fed diet containing 50 % of substitution, as well as a significant increase in the pH and ammonia of the caecum. The best nutrient digestibility coefficients and the lowest cost/kg of liveweight gain were obtained in rabbits fed 30 % of substitution. They concluded that it is possible to replace 30 % of DDGS (or 18.75 % of the diet) as protein source in rabbit feeding.
Both results show that DDGS can partially replace the protein in the diet, without negative effects on the development of growing rabbits.
F) STUDIES ON COMBINATION OF DDGS WITH DIFFERENT ENZYMES
In this regard, Liñán (2012) conducted an experiment to evaluate the use of DDGS and enzymes (hemicellulases and glucanases) in growing rabbits to see their effect on carcass composition and meat quality. For this, this author used four diets, which consisted of a basal diet (T1) based on alfalfa hay, milled grain of sorghum and soybean meal, T2 = basal diet, added with hemicellulases enzymes and glucanases, T3 = basal diet including 30 % DDGS and T4 = basal diet supplemented with hemicellulase and glucanase enzymes, and with 30 % DDGS. Liñán (2012) found a higher proportion of loin in rabbits that received diets without DDGS. The proportion of legs was increased in rabbits fed diets supplemented with enzymes, but without inclusion of DDGS (T2), whereas this effect was not observed in rabbits consuming diets containing DDGS. The chemical composition of rabbit leg meat was similar between treatments. In conclusion, the inclusion of hemicellulase and glucanase enzymes in the diet of growing rabbits did not have major effects on carcass composition or meat quality, so the inclusion in the diet of up to 30 % of DDGS was recommended, without affecting those indicators. Khattab et al . (2014) eva l ua t e d t he pa rt i a l replacement of maize and soybean meal by DDGS and supplementation with a natural multi-enzymatic complex (Allzyme SSF®) consisting of seven active enzymes: amylase, beta-glucanase, protease, cellulase, pectinase, phytase and xylanase, in a factorial arrangement of 2x3, with the use of weaned rabbits at 30 d of age. Diets included 0 or 0.02 % of the enzyme complex and the inclusion of 0, 10 or 20 % of DDGS, forming six experimental diets. Rabbits had free access to their respective diets. In the results, these levels of DDGS and the enzymatic complex did not influence on weight, gain and food intake. However, the feed conversion decreased with the inclusion of 20% DDGS, without supplementation of the enzyme complex.
Both studies show the feasibility of the combination of DDGS with hemicellulase and glucanase enzymes and with the combination of the natural multi-enzymatic complex Allzyme SSF®. The use of enzymes in diets of animals increases the availability and digestibility of nutrients in food and, thereby, improves animal performance.
G) STUDIES WITH DDGS FROM DIFFERENT SOURCES
Alagón et al. (2014) conducted a research to determine the productive performance and the caecal development of growing rabbits. For this, four experimental diets were formulated: T1 = control diet without DDGS, T2 = inclusion of 20 % of DDGS of barley, T3 = inclusion of 20 % of DDGS of wheat, T3 and T4 = inclusion of 20 and 40 % of DDGS of maize, respectively. At 59 d of age, they found that rabbits fed 20 % of DDGS of wheat achieved higher weight gain and dry matter intake, which did not differ from rabbits that received 20 % of DDGS of barley and maize. Food conversion was significantly better in rabbits fed 20 % of DDGS of maize, which only differed from rabbits that ingested DDGS of barley. The weight of the full digestive tract and full stomach did not show differences among treatments. The weight of caecum was higher in the animals of control group and differed from those fed 20 and 40 % of DDGS of maize. The authors concluded that the inclusion of DDGS of barley, wheat or maize in the diet of fattening rabbits up to 20 % can be an interesting alternative, since adequate productive yields are obtained, without negative consequences in the digestive tract of rabbits.Alagón et al. (2015) published their results with the use of DDGS from different sources (20 % of DDGS of barley, 20 % of DDGS of wheat and 20 or 40 % of DDGS of maize) in the quality of carcass and meat of the Longissimus dorsi muscle of fattening rabbits. They found no effects on most of the carcass features, texture or water retention capacity. Rabbits fed 20 % of DDGS of barley had higher percentage of fat (inguinal, scapular and dissectable) with respect to the control diet. The reddish color of the meat and pH was more evident in rabbits fed DDGS of wheat. The concentration of meat proteins and saturated fatty acids decreased with the inclusion of 40 % of DDGS of maize. These researchers concluded that the use of DDGS, regardless of the source of the grain, did not affect most traits of carcass and meat quality in rabbits. However, DDGS of barley increased the percentage of fat and wheat DDGS increased, also, the reddish color of the meat.
In summary, in growth-fattening rabbits, the studies cited in this review (Bernal et al. 2010, Soliman et al. 2010, Vázquez et al. 2011, Petkova et al. 2011, Amani et al. 2012, Liñán, 2012, Vázquez et al. 2013, Vázquez 2014, Rohloff Junior 2015 and Vázquez et al. 2016) have demonstrated the possibility of including up to 30 % of DDGS, without negative effects on the performance, digestibility and morphometry of digestive organs, as well as on the performance of the carcass of animals. However, other studies (Mohamed et al. 2013) suggest the possibility of including up to 40 % (table 4). Likewise, it is possible to combine DDGS with exogenous enzymes as natural alternative products to complement the endogenous enzymatic capacity and the nutritional value of feed and, thereby, improve animal performance (Liñán 2012 and Khattab et al. 2014). Research comparing the incorporation of 20 % of DDGS of barley, wheat or maize (Alagón et al 2012, Alagón et al. 2014 and Alagón et al. 2015) into the performance of rabbits indicate that it is possible to include them in the diet, regardless of the source of the grain.
Table 4 Effect of DDGS on the productive performance of growth-fattening rabbits
a Basal diet (sorghum and soybean)
b Basal diet (maize, barley, wheat and soybean)
c Basal diet (maize and soybean)
d Basal diet (barley, wheat and soybean)
e Basal diet (maize, wheat and soybean
It should be noted that the differences found in the cited research may be related to the variability in the form of presentation of food and types of diets. It would also be necessary to consider the factors that could have an impact on the results of the different researches, such as age, weight at the beginning of the experimental phase, breed, environment and sex, among other aspects.
Although progress has been made in the studies with the use of DDGS in growing rabbits, there is still a lack of research with the use of this by-product in other rabbit categories. Similarly, studies should be conducted to determine the influence of DDGS on reproduction, prolificacy and pre-weaning growth.
ADVANTAGES AND DISADVANTAGES OF THE USE OF DDGS IN RABBITS
In rabbit nutrition, the main advantages of DDGS (maize, wheat, sorghum or barley) are their high content of protein, NDF and digestible energy and phosphorus. Similarly, its use in diets generally decreases the costs of partial or total substitution of maize and soybean, which depends on the prices of DDGS and the previously mentioned raw materials.
Several studies have demonstrated that a correct digestive transit in rabbits requires a minimum of insoluble fiber, which is between 30 and 34 % of NDF (Machado et al. 2011). This requirement can be covered by using DDGS in rabbit diets, so, together with the contributions of ADF and NDSF that DDGS possesses, they can be considered as alternative fibrous sources in the diet of rabbits.
The main disadvantage is the price of DDGS, which until the end of the first semester of this year was around 243.00 USD/t (US Grains Council 2017). In this regard, Couso (2011) and Martínez (2011) determined, by means of a formula, the limit price at which it is feasible to buy DDGS in Cuba for their inclusion in the diets for poultry and pigs. These authors reported that with import prices of soybean meal, maize meal and monocalcium phosphate, it would be feasible to buy DDGS up to 286 USD/t for poultry and $ 329 USD/t for pigs, prices that have never been reached by this by-product, despite the increase in the costs of raw materials for the production of balanced diets.
On the quality of the DDGS protein, studies carried out on pigs (Stein et al. 2006) showed a reduction of lysine digestibility related to the thermal treatment of this by-product. Apparently, this unfavorable aspect was not evident in rabbits. In this regard, Alagón (2012) obtained digestibilities for lysine of 78.4, 85.4 and 88.2 % in diets prepared with DDGS of barley, maize and wheat, respectively, in rabbits, which are much higher results than data reported by Stein et al. (2006) in pigs. It is probable that cecal digestion and cecotrofagia would reduce this effect, because, in rabbits, the amino acids produced by bacteria may be available through this way (especially lysine, sulfur amino acids and threonine).
Another unfavorable aspect to consider is the mycotoxin content of DDGS. According to the US Grains Council (2007), in the process of ethanol production and subsequent development of DDGS, mycotoxins are not destroyed, therefore, their original concentration in cereals triples in DDGS.
When information on the mycotoxin content of a batch of DDGS is not available, it is most appropriate to include a maximum of 10 % of DDGS in the diets for rabbits, because with this dose, concentrations of mycotoxins in the diet do not exceed those that provides 30 % of maize not characterized for mycotoxins, which is something very common in international practice.
It can be concluded that dried distillery grains with solubles constitute, due to their nutritional properties, an alternative for rabbit feeding. The high content of protein, digestible energy, NDF and phosphorus of this by-product makes dried distillery grains with solubles a partial substitute for some protein ingredients that can be very expensive in the market, such as soybean meal; energy foods, such as maize, and minerals, like phosphorus (mono- or di-calcium phosphate).
