Effect of Beta-propeller Phytase from Pichia pastoris on Energy Partition in Juvenile Litopenaeus vannamei Fed a Plant Protein-Based Diet

The main objective of this study was to evaluate the effect of a new isolated exogenous Beta-propeller phytase (FTEII) obtained from Pichia pastoris, on growth, survival and energy partition of juveniles of Litopenaeus vannamei fed a plant protein diet. Two treatments were designed for the experiment: a plant protein-based diet without phytase (T1), and adiet comprisingpretreated plant protein with Beta-propeller phytase (T2). The gowth rate monitored over 30 days significantly improved when phytase was added to the diet (T2) compared to control T1(p<0.05), and survival rates were similar between treatments (p>0.05). Energy partitioning was affected by basal metabolism (HeE) which was similar in both dietary treatments (p> 0.05) but the heat increment of feeding (HiE) was higher with T1 than T2 (p<0.05), whereas retained energy (RE) increased in T2 compared to T1 (p<0.05). In summary, exogenous phytase added to a plant protein-based diet decreased the negative effect of phytic acid, released phosphorus, and therefore improved weight gain.

Net energy gained by northern fur seals (Callorhinus ursinus) is impacted more by diet quality than by diet diversity

Understanding whether northern fur seals (Callorhinus ursinus (L., 1758)) are negatively affected by changes in prey quality or diversity could provide insights into their on-going population decline in the central Bering Sea. We investigated how six captive female fur seals assimilated energy from eight different diets consisting of four prey species (walleye pollock (Gadus chalcogrammus Pallas, 1814, formerly Theragra chalcogrammus (Pallas, 1814)), Pacific herring (Clupea pallasii Valenciennes in Cuvier and Valenciennes, 1847), capelin (Mallotus villosus (Müller, 1776)), and magister armhook squid (Berryteuthis magister (Berry, 1913))) fed alone or in combination. Net energy was quantified by measuring fecal energy loss, urinary energy loss, and heat increment of feeding. Digestible energy (95.9%–96.7%) was high (reflecting low fecal energy loss) and was negatively affected by ingested mass and dietary protein content. Urinary energy loss (9.3%–26.7%) increased significantly for high-protein diets. Heat increment of feeding (4.3%–12.4%) was significantly lower for high-lipid diets. Overall, net energy gain (57.9%–83.0%) was affected by lipid content and varied significantly across diets. Mixed-species diets did not provide any energetic benefit over single-species diets. Our study demonstrates that diet quality was more important in terms of energy gain than diet diversity. These findings suggest that fur seals consuming low-quality prey in the Bering Sea would be more challenged to obtain sufficient energy to satisfy energetic and metabolic demands, independent of high prey abundance.

Juvenile salmon with high standard metabolic rates have higher energy costs but can process meals faster

Basal or standard metabolic rate (SMR) has been found to exhibit substantial intraspecific variation in a range of taxa, but the consequences of this variation are little understood. Here we explore how SMR is related to the energy cost of processing food, known as apparent specific dynamic action or the heat increment of feeding. Using juvenile Atlantic salmon Salmo salar , we show that fishes with a higher SMR had a higher peak and a greater total energy expenditure when digesting a given size of meal. However, the duration over which their metabolism was elevated after consuming the meal was shorter. The greater energy costs they incur for processing food may be related to their assimilation efficiency. These relationships are likely to have implications for feeding strategies and growth rates, since individuals with a higher SMR have higher routine costs of living but recover more quickly following feeding and so may have a greater potential for processing food.

Thermal substitution and aerobic efficiency: measuring and predicting effects of heat balance on endotherm diving energetics

For diving endotherms, modelling costs of locomotion as a function of prey dispersion requires estimates of the costs of diving to different depths. One approach is to estimate the physical costs of locomotion ( P mech ) with biomechanical models and to convert those estimates to chemical energy needs by an aerobic efficiency ( η = P mech / V o 2 ) based on oxygen consumption ( V o 2 ) in captive animals. Variations in η with temperature depend partly on thermal substitution, whereby heat from the inefficiency of exercising muscles or the heat increment of feeding (HIF) can substitute for thermogenesis. However, measurements of substitution have ranged from lack of detection to nearly complete use of exercise heat or HIF. This inconsistency may reflect (i) problems in methods of calculating substitution, (ii) confounding mechanisms of thermoregulatory control, or (iii) varying conditions that affect heat balance and allow substitution to be expressed. At present, understanding of how heat generation is regulated, and how heat is transported among tissues during exercise, digestion, thermal challenge and breath holding, is inadequate for predicting substitution and aerobic efficiencies without direct measurements for conditions of interest. Confirming that work rates during exercise are generally conserved, and identifying temperatures at those work rates below which shivering begins, may allow better prediction of aerobic efficiencies for ecological models.

Biological basis for variation in residual feed intake in beef cattle. 1. Review of potential mechanisms

There is a growing body of evidence that there is genetic variation in beef cattle feed intake relative to their liveweight and weight gain. Difference in feed intake, above and below that expected or predicted on the basis of size and growth, is measured as residual feed intake. Variation in residual feed intake must be underpinned by measurable differences in biological processes. This paper summarises some plausible mechanisms by which variation in efficiency of nutrient use may occur and presents several testable hypotheses for such variation. A� companion paper [Richardson and Herd (2004) Aust. J. Exp. Ag. 44, 431–441] presents results from experiments on cattle following divergent selection for residual feed intake. There were at least 5 major processes identified by which variation in efficiency can arise. These are associated with variation in intake of feed, digestion of feed, metabolism (anabolism and catabolism associated with and including variation in body composition), activity and thermoregulation. The percentage contribution of different mechanisms, to variation in residual feed intake, was: 9% for differences in heat increment of feeding; 14% for differences in digestion; 5% for differences in body composition; and 5% for differences in activity. Together, these mechanisms may be responsible for about one-third of the variation in residual feed intake. The remaining two-thirds were likely to be associated with heat loss due to variation in other processes, such as protein turnover and ion transport. There is no shortage of candidate mechanisms that, singularly or in combination, might contribute to genetic variation in energy utilisation in ruminants. Further research in beef cattle, to better define these mechanisms and enable their incorporation into breeding programmes, may lead not only to cattle which eat less for the same performance, but are superior in other traits as well.