Energy: Protein Ratio in Ruminants: Insights from the Intragastric Infusion Technique

Studies on energy:protein ratio in ruminants are constrained by rumen fermentation since it governs nutrient metabolism and the ratio of energy:protein yielding nutrients available for absorption. By circumventing rumen fermentation, the total intragastric infusion technique (IIT) allowed objective quantification of maintenance energy and protein requirements, volatile fatty acid utilisation efficiency, efficiency of energy utilisation for maintenance (Km) and growth (Kf) and the origin of N retention responses to independent variation of energy and protein intake. This review outlines the key IIT findings and whether they are reflected in current feeding systems with implications for different production systems worldwide. Maintenance energy requirements are similar to those derived from comparative slaughter but maintenance N requirements are significantly lower. No differences in utilisation efficiency exist between acetic, propionic and butyric acids. At low energy intakes, endogenous energy reserves are utilised to retain amino acids and fuel substantial tissue protein gains. The use of fasting metabolism to measure the utilisation of nutritionally balanced diets is questioned since it is a glucose-deficient state. Inter-species differences in glucose metabolism appear to exist, suggesting that glucose requirements may be higher in cattle than sheep. The difficulty in predicting nutrient requirements, particularly protein, with any one technique is highlighted.

Lactate and the GPR81 receptor in metabolic regulation: implications for adipose tissue function and fatty acid utilisation by muscle during exercise

Lactate is increasingly recognised to be more than a simple end product of anaerobic glycolysis. Skeletal muscle and white adipose tissue are considered to be the main sites of lactate production and release. Recent studies have demonstrated that there is a specific G-protein coupled receptor for lactate, GPR81, which is expressed primarily in adipose tissue, and also in muscle. Lactate inhibits lipolysis in adipose tissue by mediating, through GPR81, the anti-lipolytic action of insulin. A high proportion (50 % or more) of the glucose utilised by white adipose tissue is converted to lactate and lactate production by the tissue increases markedly in obesity; this is likely to reflect a switch towards anaerobic metabolism with the development of hypoxia in the tissue. During exercise, there is a shift in fuel utilisation by muscle from lipid to carbohydrate, but this does not appear to be a result of the inhibition of lipolysis in the main adipose tissue depots by muscle-derived lactate. It is suggested instead that a putative autocrine lactate loop in myocytes may regulate fuel utilisation by muscle during exercise, operating via a muscle GPR81 receptor. In addition to being an important substrate, lactate is a key signal in metabolic regulation.

Combined pre-degradation and anaerobic digestion for the treatment of a baker's yeast factory effluent

A Chryseomonas luteola strain was isolated from raw baker's yeast factory effluent as the dominant part of the microbial community and evaluated for its biodegradative activity, using the raw effluent as substrate. The strain was able to utilise the raw effluent and produce higher concentrations of energetically favourable metabolites and thereby, could contribute to the first degradation step in an anaerobic biological treatment process. A 3×4×3 factorial design indicated optimal degradation conditions in a specific environmental framework of 48 h incubation time, COD concentration of 30 g/l, pH of 6.0 and temperature of 35°C. The C. luteola strain was thereafter used in a pre-degradation step followed by an anaerobic digestion step in a 5 1 laboratory-scale hybrid digester. With the use of the pre-degraded effluent, significant improvements were found in the overall anaerobic digestion performance. These included increased COD (>15%) and TVFA (>50%) removals, especially propionic acid (88%) removal, as well as higher biogas yields (18%). The results also showed a prominent improvement in fatty acid utilisation and methanogenesis. The pre-degradation step resulted in better process control and increased stability of the system, even at relatively high organic loading rates (10 kg COD/m3.d). When the raw effluent was not pre-treated (control bioreactor), no improvement in bioreactor efficiency was observed.