Biofuel co-products as livestock feed - Opportunities and challenges

362Biofuel co-products as livestock feed – Opportunities and challengesprotein feedstuff, such as fishmeal (NRC, 1993). Highavailability of amino acids from DJKM for this fish speciesis expected. In general, the digestibility coefficientsobtained for various jatropha constituents have been high,indicating that a large percentage of those constituents aredigested and absorbed by the fish for further metabolism.Lipid digestibility of DJKM-based diets ranged from 74 to90 percent (Kumar, Makkar and Becker, 2011a). High inclusionlevels of DJKM (>50 percent fishmeal protein replacement)decreased lipid digestibility probably because of itshigh content of non-starch polysaccharides (NSPs) (Kumar,Makkar and Becker, 2011a, b).Intestinal amylase, protease and lipase activities for thecontrol group were significantly higher (P 50 percent replacement of fishmeal protein byDJKM leads to significantly lower growth and higher feedconversion ratio (feed/body mass gain) in common carp,which could be attributed to factors such as: Lower digestibilities of protein and energy in the diets,leading to lower protein and energy availability fromDJKM (plant protein structures in general are much morecompact than fishmeal protein, so digestive enzymes actslowly on DJKM proteins). The DJKM contains large concentrations of antinutrientssuch as phytate and non-starch polysaccharides (NSPs),and these could adversely affect feed utilization. The digestibility of synthetic lysine, which was added asa supplement to the diets, may be less than that of thenatural amino acid present in the feed ingredients.Retention of nutrients in the whole bodyThe efficiency with which nutrients and energy are retainedfrom feeds provides a useful assessment of the efficiencyof nutrient utilization from diets (Cho and Kaushik, 1990;Booth and Allan 2003; Glencross et al., 2004). Feedingtrials performed by Kumar, Makkar and Becker (2011a,2010c) showed that inclusion of DJKM in a common carpdiet exhibited significantly higher lipid deposition in thewhole body than in the control group. The increase inwhole body fat content on using dietary DJKM-based dietscould be due to the higher content of total carbohydrate inthese diets. Carbohydrates can be converted to lipids in thebody by lipogenesis (Kumar, Makkar and Becker, 2011a).There is evidence that replacement of fishmeal protein byplant protein sources such as maize gluten meal and soyprotein concentrates increases hepatic lipogenic enzymeactivities in fish (Dias 1999; Kaushik et al., 2004), leadingto higher whole body lipid. In fish (salmonids), increasesfound in whole body fat content with the use of dietaryplant proteins, were explained by imbalances in amino acidconcentrations (Kaushik et al., 2004; Bjerkeng et al., 1997).Furthermore, it is suggested that unbalanced amino acidcomposition influences energy metabolism. Vilhelmssonet al. (2004) found an up-regulation of several proteinsinvolved in energy metabolism in fish liver when fed plantproteins (maize gluten meal, wheat gluten, extruded wholeheat, extruded peas and rapeseed meal) and concludedthat the plant proteins increase energy demands of fish.Another possible reason could be a greater supply of someof the dispensable amino acids, such as glutamic acid,in excess by the DJKM proteins that could have led tohigher lipid retention. Involvement of possible metabolicor endocrine mechanisms in eliciting such differences inwhole body lipid deposition is suggested (Kumar, Makkarand Becker, 2011a, b). Proficient protein synthesis requiresadequate availability of all EAAs. Unbalanced amino acidconcentrations in a common carp diet resulted in increasedprotein degradation, and thereby increased protein turnover(Langar et al., 1993; Kumar, Makkar and Becker,2011a, b; Martin et al., 2003). Generally, the plant proteinbaseddiets decreased nitrogen retention in fish and shrimpbecause these diets have less digestible energy and anamino acid profile that is sub-optimal for muscle growth.Interestingly, Kumar, Makkar and Becker (2011a) showedthat when compared with fishmeal, feeding DJKM to commoncarp led to higher whole body crude protein content,showing that DJKM contains optimum digestible energyand has a balanced amino acid profile ideal for fish growth.Dietary inclusion of DJKM reduced the cholesterol level