Worldwide defective soybean grains are considered improper for use in animal nutrition, since it is generally assumed that these types of grains always contain mycotoxins and have a low nutritive value. However, as mentioned before, there is no information on the potential of DSG as a protein source in ruminant nutrition. To our knowledge, this is the first study evaluating the use of defective SBG in animal nutrition, since no paper published was found in PUBMED search platform relate to this topic, except studies where soybean grains were artificially damaged by heating to increase rumen undegradable protein [6, 7]. Thus, this paper brings new information regarding the potential use of Defective SBG as a protein source for ruminants by using growing ewes as animal model.
To obtain more precise information regarding the nutritive value of defective soybean grains (SBG), we evaluated in this study partially fermented and completely fermented SBG by chemical analyses, by in vitro and in vivo studies, as well as by analyses of mycotoxins.
Considering that SBG is a major protein source in animal nutrition the analysis of CP content in defective SBG is a primary analysis to be investigate. In this study, defective SBG presented a CP content 2% higher than that observed for ST-SBG (Table 2), as well as 13% higher CF contents on Defective grains than on ST-SBG. Similar to our data, Souza [8] observed an increase on CP and CF contents in defective grains, while Andrade [9] reported a positive correlation between defective grains and protein content. An increase in CF content was also observed by Hou and Chan [10], while. Wilson et al. [11] observed an increase of 7.1 and 3.3% on CP and CF contents in SBG with 80% damages caused by fungi. Contrarily, Ramos et al. [2] found lower lipid values for completely fermented and burned grains than ST-SBG.
The reduction in the TC content probably explains the higher CP and CF contents in defective SBG compared to standard SBG, which was 16.89 and 5.99% lower in CF and PF than that found in standard SBG. The lower TC content in defective SBG can be associated to oxidation of carbohydrates by grain metabolism as well as by microorganisms growing in the SBG [2].
A very interesting result found in this study is that additionally to higher CP content in Fermented SBG their CP present high proportion as rumen-undegrable protein and consequently lower proportion of RDP than Standard grain, estimated by in situ incubation. Although we have no information regarding how the Defective Grains were obtained and conserved in the farms, we could infer that the higher RUP in Fermented SBG was caused by high temperatures during fermentation process.
The higher RUP found in Fermented SBG were confirmed by N-NH3 concentrations in ruminal fluid from in vitro incubations, where Fermented SBG presented lower values than Standard Grain. However, NH3-N concentrations observed in vitro for experimental diets can be considered adequate for microbial fermentation according to the values suggested by Satter and Slytter [12], which apparently do not limit microbial growth, even those observed for Defective SBG, which present higher RUP proportion.
Considering than SBG presents high CP content and high proportion of its CP as RDP, it needs to be highlight since the research related to decrease the rumen degradability is well known in ruminant nutrition since 1970-1980s [6, 7], aiming to increase the efficiency of N use by animals fed its CO source. Since, animals fed high CP diets or high RDP trend present higher NH3-N concentrations in the rumen, which is associated to higher nitrogen losses via urine and lower efficiency of use of N [13]. Thus, considering the higher RUP in Defective Grains it would be infer that their use in ruminant diets could help to decrease the N excretion by urine and to improve N efficiency use by the animal.
Volatile fatty acids are the end products of the organic matter fermentation by rumen microorganisms and represent a major energy source for ruminants [14]. In our in vitro study, although there were no differences in total VFAs among the soybean grain types evaluated alone, there higher proportion of propionate for CF-SBG could indicate the lower methane production from fermentation its grain compared to ST-SBG. Also, Defective grains presented lower isovalerate and valerate than Standard SBG, indicating a lower fermentation of amino acids, what according with lower RDP in Defective Grains.
The lower IVDMD observed to Fermented SBG compared to Standard SBG can be explained by higher iNDF in Fermented SBG, since iNDF is not digested by rumen microorganisms [15] or by animal enzymes. Also, it can be explained by higher crude fat content in Fermented SBG than in Standard, since a higher crude fat content can inhibit rumen microorganisms [16]. As consequence of its lower IVDMD, it was observed lower final gas production (Vf) for Fermented than Standard SBG, as well as by its higher CP and CF content, which are nutrients components known to produce less gas when fermented in vitro than carbohydrates [17].
Although we detected significant differences in the chemical composition among standard and Fermented SBG, especially regarding CP, CF and iNDF contents as well as lower Vf, k and IVDMD values for Fermented SBG, such differences were not sufficient to affect these variables when we incubated diets containing the three types of grains. This can be explained by the dilution effect of soybean grains in the diets since SBG is added to experimental diets with a low participation in the total dry matter of the diet (17.5%).
Corroborating in vitro study in which SBG grains were evaluated as dietary ingredients and did not cause any negative effect on gas production and IVDMD, replacement of Standard by Fermented SBG did not cause negative effects on intake and digestibility of nutrients. This is a very important finding since dry matter intake is the most important variable affecting animal productivity, where 60 to 90% of the variation observed in digestible energy intake could be explained by DMI variation, whereas digestibility only explained 10–40% of this variation [18, 19, 20]. Thus, the absence of a negative effect of Fermented SBG on DM intake is a good indicator of its potential to be used in diets for ruminants.
The average values of dry matter digestibility (810.8 g.kg‑1) are considered adequate for grain-based diets, which are based on corn grain, where starch is the major component (around 72% in the flint corn), since starch is a non-fibrous carbohydrate and can be rapidly and almost completely digested in the gastrointestinal tract (GIT), contrarily to fibrous carbohydrates, which are slowly and incompletely available in the GIT [21]. The digestibility coefficients obtained in this study for DM were similar those observed by Reynolds et al. [22] for diets containing 75% concentrate (79.7%), using growing beef heifers as animal model, as well as the values found by Poore et al. [23], who obtained DM digestibility values ranging from 70.3 to 80.0% for diets containing 60 and 90% concentrate, respectively.
As consequence of the absence of effect on nutrient intake and digestibility, replacing Standard by Fermented SBG also did not affect animal performance or feed efficiency. The average values of animal performance variables can be considered as normal for crossbreed ewes used in Brazil in terms of ADG (177 g.animal-1), CY (49.55%), and EF (0.218 kg of body weight gain.kg-1 of feed) [24, 5].
Considering that performance variables are the most important variables evaluated by producers to select the suitable technology, given the lower cost of defective SBG associated with same animal performance proportioned by Standard SBG, the use of Fermented SBG would be a good alternative for ruminant producers which are located close to SBG farms, in order to reducing diet costs and improving the profit associated with ruminant production.
Thus, Fermented SBG presents potential to replace Standard SBG in ruminant diets without having negative effects on animal health and productivity. However, considering its lower cost, Fermented SBG can help producers to reduce the cost of diets and, thus, to increase the profit.