Chemical composition and <em>in vitro</em> evaluation of the feeding value of brewery by-products for ruminants

Abstract

Livestock production plays a crucial role in food security and nutrition, especially in developing countries. In Ethiopia with its huge livestock population – more than two-thirds of population own livestock – lack of feed is a critical challenge, and the productivity of livestock remains very low. Feed scarcity in terms of quantity and quality is one of the key constraints for livestock to reach the potential productivity level. In this regard, utilisation of non-conventional feed resources efficiently becomes a considerable alternative to tackle feed scarcity and improve productivity. Use of cereals as ruminant feed in Ethiopia is unlikely considering its shortage and the direct competition with humans. Brewery by-products cost less than concentrate feeds and, as a supplement, could enhance protein and energy values of low-quality cereal crop residues and herbage from pastures. However, brewery by-products are highly variable feeds in terms of chemical composition and the nutrient value related to the brewing processes, and type of cereal grains used. These variables in turn may vary based on breweries and localities. Hence, the main goal of this thesis was to evaluate chemical composition and in vitro feeding value of brewery by-products – brewers grains (BG), and tella-atella (TA): a by-product of locally produced tella drink – obtained from Ethiopia; and investigate the potential variability within and between brewery by-products. The first part of the thesis comprises a review focusing on the chemical composition, feeding value, and storage and preservation conditions of BG as a ruminant feed in general and without restriction to Ethiopia. In addition, the review analyzes factors contributing to the variation of chemical composition of BG. Based on the findings of the review, the variables of the brewing processes, malt barley varieties used, and cereal grains added are main factors that contribute to the variation in chemical composition and nutrient value of BG. Particularly, several enzymes produced during malting and mashing processes, and use of several heat treatments (temperature regimes) are key factors of brewing processes influencing the components that hydrolyzed in to wort, and the components that remain in the BG. Both variables are interrelated, and the production and activity of the enzymes again depend on the specific optimal temperature used. In the second part, in vitro methods were applied to examine nutritive value of BG and TA samples with particular focus on crude protein (CP); and investigate the potential variability. A total of 17 samples of BG obtained from nine breweries, representing about 70% of the total available breweries in Ethiopia, and 3 TA samples were collected, and subjected to analysis of chemical composition and CP fractionation. Moreover, an in vitro rumen gas production technique was applied to estimate energy values, ruminally undegradable feed CP (RUP) and utilisable CP at the duodenum (uCP). The overall results show that BG and TA are relatively high in most nutrients, mainly containing high CP and neutral detergent fibre concentrations. Both by-products contain CP with low rumen degradability indicating great potential for milk production of dairy animals provided that the RUP is accessible in the small intestine. Hence, digestibility of RUP and its amino acid patterns in the small intestine of the animal require further investigation. However, substantial variations within BG, and compared with TA were observed in terms of chemical composition and nutritive value. The attempt to relate BG to the origin of cereal grains showed the tangible influence of the original grains on the nutrient values of BG. Particularly high starch concentrations in non-pure barley malt BG, and TA samples were most likely related to the brewing process and type of grains used. Considerable energy contents of these by-products make them also valuable energy supplements especially in regions like Ethiopia where the largest portion of the available feed is roughage. Overall, findings of the thesis underline that BG and TA, both as potential protein and energy supplements, could contribute to improved livestock productivity. Thus, considering the potential to the expansion of breweries in Ethiopia, both by-products could contribute to tackle the feed scarcity for ruminants. Due to the variability in terms of chemical composition and nutritive value, a periodic evaluation of feeding value is vital for efficient utilisation of the by-products. Further studies on the digestibility of RUP and composition of amino acids in the small intestine would also be essential to utilise the by-products efficiently in feed formulation. Moreover, utilisation of an additional agro-industrial by-product as a feed supplements should be considered to meet the existing huge feed demand in Ethiopia.