Wheat distillers are a good source of energy and by-pass protein for ruminants.
In the INRA-AFZ tables, the ME content of wheat DDGS varies between 12.5 (starch less than 7% as fed) to 13.1 MJ ME/kg DM (starch over 7% as fed) (Sauvant et al., 2004). The digestibility of dried distillers grain and solubles (DDGS) from wheat and wheat/barley mixtures was 76, 50 and 87% for organic matter, crude fibre and crude fat, respectively, resulting in an ME of 12.1 MJ/kg DM, and an NE for lactation of 7.3 MJ/kg DM (Losand et al., 2009). Indigestible NDF is the major parameter determining OM digestibility. An in sacco study reported that wheat DDGS had 12% DM of indigestible NDF, similar to that of rapeseed meal (12% DM) and cottonseed meal (10% DM) but much higher than that of maize DDGS (5% DM) and soybean meal (almost zero) (Chapoutot et al., 2010). In a comparative study, rumen degradability of NDF was highest for rye distillers grain (47%), intermediate for wheat and triticale distillers grain (45%) and lowest for barley distillers grain (34%) (Mustafa et al., 2000). Though wheat DDGS is not reported to induce digestive interactions, the supplementation of wheat DDGS to a barley-based finishing diet reduced OM digestibility values, with no effect on DE content (Walter et al., 2012).
In a comparison of different grains as ethanol sources, the effective protein degradability of wheat DDGS (54%) was found to be similar to that of rye DDGS and triticale DDGS (54 and 51%, respectively) and significantly higher than that of barley DDGS (49%). The protein degradability of thin stillage derived from wheat (60%) was lower than that of thin stillages derived from rye or triticale (59 and 53%, respectively), but higher than that of thin stillage from barley (48%) (Mustafa et al., 2000).
Wheat DDGS are, with maize DDGS and soybean meal, one of the best sources of by-pass protein, better than all other untreated oil meals (Nuez-Ortin et al., 2010). In a meta-analysis of a database of in situ protein degradability, wheat DDGS was reported to have an effective protein degradability (for a transit outflow rate of 6%/h) of 56±5% (n=12). This value was lower than that of rapeseed meal (73±6%, n=3) and corn gluten feed (70±6%, n=9), but similar to that of soybean meal (59±5%, n=8) and higher than that of maize DDGS (46±4%, n=14), dried brewers grains (43±6%, n=4) and formaldehyde-treated soybean meal (33±9%, n=2) (Chapoutot et al., unpublished). Wheat DDGS are also a good source of rumen degradable protein: wheat DDGS supplementing a barley-based finishing diet increased linearly rumen NH3-N concentrations and N excretion (McKeown et al., 2010a; Walter et al., 2012).
The apparent digestibility of protein in the small intestine (determined by a mobile nylon bag technique, Yue Qun et al., 2007), of wheat DDGS was reported to be 90%. This value was lower than that of soybean meal or groundnut meal (96%), similar to that of corn gluten meal (91%) and maize (90%), but higher than that of cottonseed meal (81%), rapeseed meal (82%) and brewers grains (74%), and much higher than that of alfalfa hay (40%) and maize straw (36%). The INRA-AFZ tables (Sauvant et al., 2004) and the meta-analysis of Chapoutot et al. (unpublished) reported the following values of apparent digestibility of protein in the small intestine: wheat DDGS (85 and 93%); maize DDGS (90 and 93%); soybean meal (96 and 98%); cottonseed meal (90 and 86%); and rapeseed meal (79 and 70%). It can thus be considered that by-pass protein of wheat DDGS has a good intestinal digestibility and is one of the best sources of metabolizable protein. It must be noted that the by-pass protein of wheat DDGS is poor in lysine, like that of other distillers grains, which could limit performance in certain situations. One study (Nuez-Ortin et al., 2010) reported that a wheat and maize blended DDGS was a better source of truly digested and absorbed protein in the small intestine than wheat DDGS and maize DDGS separately.
It has been shown by an in vitro incubation study that wheat DDGS diets produced more microbial N and microbial DM than control and maize DDGS diets. However, this difference was too slight to affect growth in lambs (O'Hara et al., 2011). The same effect was observed in cattle (Li Chun et al., 2012).
Increased P excretion by heifers fed wheat DDGS at 20 or 40% of dietary DM presents a challenge for cattle feeders with respect to nutrient balancing (Walter et al., 2012). This is in accordance with results observed in growing lambs (McKeown et al., 2010a).
Growing and finishing cattle
Growing and finishing cattle are the major users of wheat DDGS, particularly in Canada (Newkirk, 2011). Increasing levels of wheat DDGS linearly increased DMI and reduced gain:feed ratio, but had no effect on average daily gain (Gibb et al., 2008). Wheat DDGS had a similar feeding value to barley when included at 20% (diet DM), but digestibility and energy content declined with higher levels of inclusion (Gibb et al., 2008). Replacement of barley grain with maize or wheat DDGS up to 40% (diet DM) led to higher performance (improved gain:feed ratio) with no detrimental effect on carcass yield and quality in heifers (Walter et al., 2012). Similarly, growing beef cattle could be fed on wheat distillers grain replacing barley grain without compromising feed conversion efficiency (Holtshausen et al., 2011).
In steers, there was no difference in DMI or efficiency of gain in a basal diet supplemented or not with wheat thin stillage. Carcass traits indicated a trend towards increased fat with increasing thin stillage DM concentration (Walter et al., 2012). In another trial carried out with steers, there was a linear improvement in apparent digestibility of energy of the diet as thin stillage DM concentration increased. It was concluded that supplementing growing and finishing cattle with wheat thin stillage reduced the amount of the basal diet required for gain (Fisher et al., 1999).
In heifers, a straw + ground brome hay based diet supplemented with either wheat DDGS, soybean-canola, or grain-canola did not alter intake, passage rate or digestibility. More study is required to assess the feasibility of feeding these supplements at greater levels with forage-based beef cattle diets (Kerckhove et al., 2011).
Feeding triticale DDG to beef cattle did not affect carcass and meat quality but it increased n-3 fatty acids and reduced trans-fatty acids contents in the meat (He et al., 2012).
Effects on feeding behavior and digestion in cattle
Moderate amounts of wheat DDGS were used to replace both barley grain and silage to meet energy and fibre requirements of finishing cattle. However, when silage content was very low (under 10%), wheat DDGS was not an efficient fibre source and it decreased rumen pH even though the rapidly fermentable starch content of the diet was considerably reduced (Li et al., 2011). When barley grain was replaced with wheat DDG and maize DDG in diets fed to growing beef cattle feeding behaviour and incidence of rumen acidosis were unchanged (Holtshausen et al., 2011). Increasing the inclusion rate of wheat DDGS in a barley-based finishing cattle diet resulted in decreasing rumen propionate levels, whereas butyrate level increased (Walter et al., 2012). Replacement of barley grain with up to 40% wheat or maize DDGS did not mitigate rumen pH conditions associated with mild to moderate acidosis in heifers fed a barley-based finishing diet (Walter et al., 2012).
Because of its protein content, wheat DDGS can be used as a substitute to rapeseed meal and even sometimes to soybean meal. Studies have shown that this substitution does not affect rumen fermentation, microbial protein production and milk yield (Azarfar et al., 2013; Abdelqader et al., 2013; Chibisa et al., 2012; Franke et al., 2009; Penner et al., 2009). The partial substitution of dietary concentrates with wheat DDGS does not generally affect milk yield, milk composition or chewing activity (Penner et al., 2009). However, when wheat DDGS was used as a forage substitute, it did not promote chewing activity to the same extent as barley silage, resulting in reduced milk fat concentration and a higher risk of rumen acidosis (Penner et al., 2009). Partially replacing barley silage with wheat DDGS was able to improve productivity of lactating dairy cows, but decreased chewing time, rumen pH, and milk fat concentration. That response was not alleviated by the addition of alfalfa hay (Zhang et al., 2010).
Feeding increasing amounts of wheat DDGS can alter the fatty acid profile of milk fat. There was a linear increase in milk concentrations of CLA cis-9, trans-11, trans-13, C18:1 trans-11, and total CLA, when the level of wheat DDGS increased (Chibisa et al., 2013).
In growing lambs, wheat DDGS and triticale DDGS replaced a mixture of barley grain and rapeseed meal at 20% dietary level (DM basis) without adversely affecting DM intake, average daily gain and carcass characteristics. Including triticale DDGS improved the fatty acid profile of subcutaneous fat (McKeown et al., 2010b). In lambs, triticale DDGS replaced up to 60% barley grain without adverse affects on growth performance or carcass traits (McKeown et al., 2010a). In finishing lambs, replacing rapeseed meal and part of the barley grain with 20% (DM basis) of either high-oil maize DDGS, low-oil maize DDGS or wheat DDGS, maintained healthy rumen function, growth performance and carcass characteristics (O'Hara et al., 2011).