Brewers grains are a good ingredient for ruminants, quite typical in beer-producing countries.
Digestibility and energy value
Values of OM digestibility found in the literature are variable and range from 55 to 75%. Feed tables from different regions report OM digestibilities from 59% to 67% (Sauvant et al., 2004; Beyer et al., 2003; MTT, 2013; Volden, 2011). It should be noted that chemical composition is not a significant predictor of OM digestibility in brewers grains (Sauvant, 2013, personal communication). Dried brewers grains are sometimes reported to have a lower OM digestibility than wet brewers grains (59 vs. 63%, MTT, 2013; 64 vs. 66-67%, Beyer et al., 2003), which is probably due to the heat treatment. However, a higher drying temperature (240° vs. 180°) was found to slightly increase the in vitro digestibility of brewers grains (Mesgaran et al., 2011).
The energy value for dried brewers grains, expressed as Net Energy for lactation, ranges from 5.8-6.0 MJ/kg DM (Sauvant et al., 2004; MTT, 2013) to 6.4-7.0 MJ/kg DM (Volden, 2011), and up to 7.8 MJ/kg DM (NRC, 2001). As a consequence, the value of brewers grains relative to other feeds is itself variable. For instance, feed tables usually consider brewers grains as a better ingredient than tomato pomace (Beyer et al., 2003; NRC, 2001) but one study found the opposite (Aghajanzadeh-Golshani et al., 2010).
Brewers grains have a good protein value for ruminants, and are relatively rich in rumen undegradable protein compared to feeds derived from other plants. Brewers grains are thus often used in ruminant production systems with high requirements for by-pass protein, such as high-yielding dairy cows. The effective nitrogen degradability of brewers grains reported in feed tables and in the scientific literature is about 41-49% (Sauvant et al., 2004; Batajoo et al., 1998; Nishiguchi et al., 2005; Volden, 2011; Promkot et al., 2007). These values are lower than those of soybean meal and cereal by-products (Sauvant et al., 2004; Volden, 2011; Nishiguchi et al., 2005), though in one case the protein of distillers dried grains was found less degradable (Batajoo et al., 1998). Nitrogen degradability depends on the amount of heat used during the drying process: in one experiment, the amount of by-pass protein doubled when the temperature rose from 50° to 135°C (Pereira et al., 1998). Heating also decreases protein solubility while increasing the insoluble ADF-bound nitrogen fraction (Enishi et al., 2005). Values for the intestinal digestibility of nitrogen range from 74% (Yue Qun et al., 2007) to 84% (Sauvant et al., 2004), which is much lower than the values reported by these authors for soybean meal, corn gluten meal and maize distillers grains (more than 90%). As usual for cereal grains and their by-products, lysine is the first limiting amino acid in brewers grains used for high yielding ruminants, so it needs to be blended with sources of by-pass protein rich in lysine.
It is usually recommended to include brewers grains up to 20-25% of the concentrate DM, and up to 15-20% of the total dietary DM. However, up to 30% has also been recommended (Ewing, 1997), and it has been shown that this rate did not affect milk production in dairy cattle (West et al., 1994). No difference in performance was observed when dried, re-wetted or wet brewers grains were fed to lactating dairy cattle (Porter et al., 1977). Dried brewers grains were found to successfully replace part of the forage in the diet (Younker et al., 1998). However, replacing soybean meal with wet or dried brewers grains in lactating dairy cattle was detrimental to performance (Hoffman et al., 1988). Brewers grain silage could be included at up to 15% in dairy diets with no effect on nutrient intake, production and quality of milk (Geron et al., 2010). Brewers grain silage was found to be a satisfactory replacement for maize silage in rations for lactating dairy cattle (Münger et al., 1997).
Brewers grains can be a source of fibre for dairy cattle. They have a positive effect on chewing time, which is higher for brewers grains (56.6 min/kg DM) than for other fibrous feeds such as beet pulp (32.3 min) and maize cob silage (41.6 min) (De Brabander et al., 1999). This is beneficial to the recycling of buffer substances in saliva, which may help to decrease the risk of acidosis.
Inclusion rates as high as 40% have been considered acceptable (Ewing, 1997). Up to 24% DM brewers grains in male growing cattle did not alter rumen fermentation (pH, efficiency of microbial protein synthesis and NH3) and OM digestibility (Geron et al., 2008). In a trial with finishing beef cattle fed with 0.5-1 kg or 1-2 kg of ensiled brewers grains, intake and growth performance were lower in the second group, while the performance of animals in the first group was similar to those fed a control diet based on maize silage. Using a pH stabiliser in cattle fed 1-2 kg of ensiled brewers grains resulted in similar performance and carcass quality as in the control group (Morel et al., 1997). Brewers grains were found to be a satisfactory replacement for corn gluten meal in rations for growing heifers (Lopez-Guisa et al., 1991).
Recommended inclusion rates of brewers grains in diets for lambs depend on the source. While some authors advise against them (Ewing, 1997), some reports are more positive. In Italy, feeding dehydrated brewers grain to lambs at up to 40% of the diet DM resulted in good growth performance, feed conversion ratio, and in fatter carcasses than with less dried brewers grains (Bovolenta et al., 1998). In tropical and subtropical areas, high inclusion rates have been used in growing sheep without depressing performance or digestibility: in Iraq, 50% of dried brewers grains in the concentrate (Baghdassar et al., 1986); in Mexico, 60% of diet DM from wet brewers grains (with no change in rumen pH and molar proportions of VFA) (Aguilera-Soto et al., 2007); in Brazil, 67% of wet brewers grains associated with Bermuda grass (Cynodon dactylon) (though it decreased DM intake) (Cabral Filho et al., 2007).
In Nigeria, the inclusion of 64% dried sorghum brewers grains resulted in higher growth performance than a diet based on maize bran, but adding urea to the latter diet gave a similar performance (Olorunnisomo et al., 2006). In another Nigerian trial, the optimal inclusion rate was 45%, as a 60% rate reduced intake and caused digestive problems (Anigbogu, 2003). In Brazil, wet brewers grains included at 30%, partially replacing maize grains, resulted in lower performance and feed efficiency than dehydrated citrus pulp (Gilaverte et al., 2011).
There are few trials on the use of brewers grains for goats. Wet brewers grains replaced up to 25% of the concentrate in diets for goats at the end of lactation but higher rates depressed diet digestibility (Silva et al., 2010). Wet brewers grains included at 20 to 40% in a total mixed ration resulted in lower nutrient digestibilities, but DM intake was higher at the 20% rate (Choi SunHo et al., 2006). In Samoa, a comparative study showed that dried or wet brewers grains were valuable feeds for goats (Aregheore et al., 2002).