Nutritional variations of brewers’ grain collected from different breweries
All chemical compositions and in vitro digestibility with exception of some nutritional parameters of wet brewery grain from the present trial were found within ranges a recent finding (Heuzé et al., 2017). However, slight deviations were noted against NRC (2001) for all measured parameters. The acid detergent fiber and neutral detergent fiber components of wet brewery grain in this study were differed with the report of Westendorf and Wohlt (2002) and dry matter was also different with the report of Senthilkumar et al. (2010). The reasons for this variations maybe speculated to a variety of factors that include: grain and/or varietal difference among the malt grain used as foundation grain, harvesting time and the conditions under which it was cultivated; the conditions used for malting and mashing and the amount and type of the adjuncts added in mixture with the barley malt during the process of wort production. In addition, period of fermentation, processing techniques and analytical procedures followed may be partly responsible for the observed variations.
In agreement to the present finding, Mussatto et al. (2006) and Waters et al. (2012) found nutritional variations among wet brewery grain (WBG) derived from brewing processes without addition of adjuncts (i.e. using 100% barley malt), but the former used Brazilian barley malt while the latter used barley malt from Ireland. Differences can also be observed when comparing the results of these authors with those reported by Meneses et al. (2013) and Carvalheiro et al. (2006) who used WBG derived from a process using barley malt with adjuncts obtained from two different Portuguese breweries. The variations observed in the results of these authors suggest that the differences in the source of malt grain and the brewing process conditions affected the composition of the residual WBG material. In fact, the conditions used for the brewing process (i.e., heat applied during the malting and mashing process, and the type of procedure followed for starch extraction during the wort filtration process etc.) were not reported in any of the studies reported and this is probably another factor with signiﬁcant influence on the results indicated in Table 2 above.
Chemical composition of brewer’s grain stored under different conservation practices
Soaking is the most prominently used wet brewery grain (WBG) conservation practice under on-farm conditions despite extensive losses in feed and microbial quality compared to the other storage methods evaluated in the current study. Sodium chloride is reported to have good anti-microbial property and often considered as “fermentation inhibitor” in feed preservation process (McDonald et al., 1991). However, sufficient scientific literature was not found to substantiate this with the result obtained from the soaking method in the present study. In line to this, the level of salt used in the soaking process and the storage duration that optimizes proper storage of fresh WBG need further research. Lower dry matter (DM) loss for the ensiled sample was a good sign of the absence of any significant degradation of nutrients during the ensiling process as compared to the other two local WBG conservation practices. Higher DM loss in the soaked and sun-dried brewery grain compared to the control (freeze-dried) and ensiled brewery grain could probably be associated to the relatively higher fungal colony count that arise from the slow sun drying process mainly attributed to the lower solar energy and to the frequent opening of the storage container for feed removal that often induces aerobic deterioration in the soaked sample. In general, during sun drying and soaking process, residual soluble carbohydrates in brewery grain possibly have been converted into ethanol, CO2 and water in the presence of large colonies of yeast and mold (McDonald et al., 1991) thereby leading to excessive loss of dry matter (DM) and other nutrients from the WBG. Moreover, in agreement to same author, the lower CP observed for brewery grain conserved using these two preservation practices could probably be associated to the extensive proteolysis that might have occurred during the open air storage conditions. The greater values of neutral detergent fiber, acid detergent fiber and permanganate lignin across the preservation practices except ensiling indicated that there were undesirable microbial activities which can be witnessed from the larger fungal colony counts in the present study, as soluble nutrients have been degraded, the proportion of fiber components tended to have proportionally increased. Likewise, lower values of digestible organic matter in sun-dried and soaked sample, can be possibly linked to the loss in DM and other soluble nutrients and a sharp increase in cell wall fractions. In a related study Baskett et al. (2009) also reported losses in DM equivalent to 8.6% and 9.6% for wet distiller grains stored in aerobic and anaerobic storage conditions in bunker silos.
Fungal load dynamics of brewery spent gain conserved under different practices
The higher fungal count in the soaked brewery spent grain (WBG) compared to the other two conservation practices and the control can be speculated to the aerobic exposure of WBG during feed removal for routine feeding on the one hand and the proportion of salt to water that might not have optimized proper fermentation partly due to lack of research recommendations for the soaking technique. Longer storage durations may also hold responsible for the larger fungal contamination seen in the soaking process. Nutrient loss from the sun drying brewery grain in the present study was also relatively higher since drying was done under a low temperature that increased risks of mold growth and mycotoxin production (Chulze, 2010). According to Thus, The efficiency of ensiling in brewery spent grain conservation has also been noted by some other authors (Heuzé, et al. 2017; Geron et al., 2008). According to Woolford (1990) and Dairy one (2017) the presence of yeasts and mold in a stored feed greater than 5.00 CFU/g DM, is considered undesirable leading to higher losses of DM and other essential nutrients. Hence, based on these recommendations both yeast and mold colony counts from the present study were considerably lower implying such feeds can safely be fed to dairy cattle. The average yeast and mold forming colony units (log CFU/g DM) obtained from the current study were slightly higher than the values of 2.7 and 1.8 which was reported earlier in aerobically and anaerobically conserved WBG using organic acids (lactic acid strains) (Marston et al., 2009), the variation being attributed to the strong inhibitory effect of the organic acid used in the latter case.
Crude protein degradability of brewer’s grain conserved under different storage practices
The result of degradability constants excluding water-soluble crude protein fraction from the current study is in line with the previous report (NRC, 2001; Kazemi et al., 2014; Heuzé et al., 2017). The variation of the “a” fraction in crude protein degradability can related with differences in the type of WBG conservational practices employed and differences in the type of washing methods (hand Vs machine). In agreement to the present finding, Gao et al. (2015) noted low repeatability for rapidly soluble ruminal and post-ruminal nitrogen and amino acids fractions of three supplemental protein sources. The ‘’c’’ and ‘’ED’’ values of CP fraction varied greatly among the conservation practices and the control sample. This variation could be related in the differences modes of dry, fresh or ensilage (Nocek, 1985. In agreement to the present finding, Kamalak et al. (2005) noted that in situ DM disappearance after 48 and 96 h to be negatively correlated with neutral detergent fiber of the WBG stored under different preservation practices. The poorest ‘ED’ and rate constant ‘c’ values in CP degradability of the ensiled wet brewery grain than the control, soaked and dried grain in the present study provided a clear evidence of ensiling have relatively lower rumen fermentable protein. Similar observations have been reported earlier by Armentano et al. (1986) and NRC (2001). The estimated rumen undegradable protein (RUP) in this study was 53.8, 43.7, 58.2 and 56.4% in control, soaked, ensiled and sun-dried samples, respectively. This estimated RUP percentage for the fresh and the remaining local storage techniques from the present study was slightly higher than the mean values reported by NRC (1989) for cottonseed meal (41%) and sunflower meal (26%) but was lower than the content of RUP for dried distillers’ grain (67.1%) (Kelzer et al., 2010). Lower potential CP degradability (a + b) values was found for the control, ensiled and sun-dried samples compared to WBG preserved using the soaking method. Similar results were noted from related research work by Promkot et al. (2007). But, in general, WBG reportedly have lower ruminal protein solubility and degradability (Armentano et al., 1986) while in-situ degradability results have been affected by different factors such as feed particle and sample size, bag material pore size; test animal diet and washing procedures (Nocek, 1985; Gao et al., 2015).