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      Level of feeding and stage of maturity affects diet digestibility and protein and fat deposition in cross-bred lambs

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          Abstract

          Metabolizable energy intake is the key determining factor for the expression of an animal’s genetic potential for growth, and current predictive growth models are not capable of accounting for all the nutritional variation that is commonly observed. The current study was designed to investigate energy transactions as lambs grow using CT scanning to assess body compositional changes at two levels of intake and two stages of maturity, and compare results to predictive equations.

          A pelleted diet was provided to cross-bred lambs ( n = 108) at approximately 2.5 and 3.5% of liveweight (LW) in dry matter when the lambs were approximately four (31.8 ± 0.3 kg LW) and eight (40.5 ± 0.3 kg LW) months of age. A digestibility trial was run sequentially using 10 lambs of the same genetic and nutritional history fed at the same feeding levels to determine the digestibility of the diet.

          In the first feeding period, metabolizable energy intake was 15.3 ± 0.03 and 9.5 ± 0.03 MJ ME/d for high and low feeding levels respectively, resulting in higher rates of empty body gain for high feeding level lambs (197.7 ± 7.8 vs. 72.8 ± 8.2 g/d; P < 0.001). In the second feeding period, metabolizable energy intake was 15.2 ± 0.01 and 12.0 ± 0.01 MJ ME/d for high and low feeding levels respectively, resulting in higher rates of empty body gain for high feeding level lambs (176.3 ± 5.4 vs. 73.9 ± 5.3; P < 0.001).

          Lambs at later stages of maturity retained proportionately more energy as fat for every unit of retained energy compared to younger lambs (95.4 ± 0.40 vs. 90.0 ± 0.42%; P < 0.001). Lambs fed the lower feeding level in period two also retained proportionately more energy as fat for every unit of retained energy than lambs at the higher feeding level (97.1 ± 0.36 vs. 94.0 ± 0.37%; P < 0.001) which is hypothesized to be because of the rapid response of visceral lean tissue to changes in nutrition. There were no significant interactions between treatments in the first and second feeding periods, indicating an absence of a compensatory gain response to a nutritional restriction in the first feeding period.

          This experiment highlights the significance of a changing feed supply and the subsequent effects on body composition and the partitioning of energy to lean and fat tissue deposition. For improvements in the accuracy of predictive ruminant growth models it is necessary to gain a greater understanding of the different tissue responses over time to changes in nutrition.

          Abstract

          Using CT scans to assess body composition, it was identified that lambs at later stages of maturity and lower levels of feeding had increased rates of fat deposition as a proportion of empty body gain. Nutritional history had no effect on the rate or composition of gain at different feeding levels, indicating that the composition of gain is driven primarily by stage of maturity and energy intake.

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          Most cited references46

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          OsiriX: an open-source software for navigating in multidimensional DICOM images.

          A multidimensional image navigation and display software was designed for display and interpretation of large sets of multidimensional and multimodality images such as combined PET-CT studies. The software is developed in Objective-C on a Macintosh platform under the MacOS X operating system using the GNUstep development environment. It also benefits from the extremely fast and optimized 3D graphic capabilities of the OpenGL graphic standard widely used for computer games optimized for taking advantage of any hardware graphic accelerator boards available. In the design of the software special attention was given to adapt the user interface to the specific and complex tasks of navigating through large sets of image data. An interactive jog-wheel device widely used in the video and movie industry was implemented to allow users to navigate in the different dimensions of an image set much faster than with a traditional mouse or on-screen cursors and sliders. The program can easily be adapted for very specific tasks that require a limited number of functions, by adding and removing tools from the program's toolbar and avoiding an overwhelming number of unnecessary tools and functions. The processing and image rendering tools of the software are based on the open-source libraries ITK and VTK. This ensures that all new developments in image processing that could emerge from other academic institutions using these libraries can be directly ported to the OsiriX program. OsiriX is provided free of charge under the GNU open-source licensing agreement at http://homepage.mac.com/rossetantoine/osirix.
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            A universal equation to predict methane production of forage-fed cattle in Australia

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              Drives and limits to feed intake in ruminants

              The control of energy intake is complex, including mechanisms that act independently (e.g. distention, osmotic effects, fuel-sensing) as well as interacting factors that are likely to affect feeding via their effects on hepatic oxidation. Effects of ruminant diets on feed intake vary greatly because of variation in their filling effects, as well as the type and temporal absorption of fuels. Effects of nutrients on endocrine response and gene expression affect energy partitioning, which in turn affects feeding behaviour by altering clearance of fuels from the blood. Dominant mechanisms controlling feed intake change with physiological state, which is highly variable among ruminants, especially through the lactation cycle. Ruminal distention might dominate control of feed intake when ruminants consume low-energy diets or when energy requirements are high, but fuel-sensing by tissues is likely to dominate control of feed intake when fuel supply is in excess of that required. The liver is likely to be a primary sensor of energy status because it is supplied by fuels from the portal drained viscera as well as the general circulation, it metabolises a variety of fuels derived from both the diet and tissues, and a signal related to hepatic oxidation of fuels is conveyed to feeding centres in the brain by hepatic vagal afferents stimulating or inhibiting feeding, depending on its energy status. The effects of somatotropin on export of fuels by milk secretion, effects of insulin on gluconeogenesis, and both on mobilisation and repletion of tissues, determine fuel availability and feed intake over the lactation cycle. Control of feed intake by hepatic energy status, affected by oxidation of fuels, is an appealing conceptual model because it integrates effects of various fuels and physiological states on feeding behaviour.
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                Author and article information

                Contributors
                Journal
                J Anim Sci
                J Anim Sci
                jansci
                Journal of Animal Science
                Oxford University Press (US )
                0021-8812
                1525-3163
                2023
                28 March 2023
                28 March 2023
                : 101
                : skad095
                Affiliations
                Fred Morley Centre, School of Agricultural, Environmental and Veterinary Sciences, Charles Sturt University , Wagga Wagga, NSW 2650, Australia
                Gulbali Institute, Charles Sturt University , Wagga Wagga, NSW 2650, Australia
                Fred Morley Centre, School of Agricultural, Environmental and Veterinary Sciences, Charles Sturt University , Wagga Wagga, NSW 2650, Australia
                Gulbali Institute, Charles Sturt University , Wagga Wagga, NSW 2650, Australia
                Fred Morley Centre, School of Agricultural, Environmental and Veterinary Sciences, Charles Sturt University , Wagga Wagga, NSW 2650, Australia
                Gulbali Institute, Charles Sturt University , Wagga Wagga, NSW 2650, Australia
                NSW Department of Primary Industries, Livestock Industries Centre, University of New England , Armidale, NSW 2351, Australia
                Author notes
                Corresponding author: tkeogh@ 123456csu.edu.au
                Author information
                https://orcid.org/0000-0002-9500-5933
                Article
                skad095
                10.1093/jas/skad095
                10132813
                36976656
                c16d91ef-0f82-4dd0-baae-0e68ac8b72b2
                © The Author(s) 2023. Published by Oxford University Press on behalf of the American Society of Animal Science.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial License ( https://creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com

                History
                : 09 August 2022
                : 26 March 2023
                : 26 April 2023
                Page count
                Pages: 11
                Funding
                Funded by: Meat and Livestock Australia Donor Company;
                Funded by: Fred Morley Centre;
                Funded by: Australian Government Research Training Program Scholarship;
                Categories
                Ruminant Nutrition
                AcademicSubjects/SCI00960

                body composition,compensatory growth,digestibility,feed intake,lamb growth,nutrition

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