Use of theoretical efficiencies of protein and fat synthesis to calculate energy requirements for growth in ruminants

dc.contributor.advisor
dc.contributor.authorRoux, Carl Z.
dc.contributor.emailcarl.roux@up.ac.zaen_US
dc.date.accessioned2014-05-05T09:51:48Z
dc.date.available2014-05-05T09:51:48Z
dc.date.issued2013-12-17
dc.description.abstractThe main objection against conventional net energy systems is that owing to variation in gain composition and the different energy contents of protein and fat, the efficiency of energy gain cannot be regarded as a growth constant. The present approach shows that the separate accommodation of protein and fat in predicting ruminant nutritional requirements can easily be achieved, since growth energy retention efficiency can be replaced by protein and fat synthesis efficiencies, together with an augmentation of maintenance with the cost of protein turnover. The synthesis efficiency of protein (kPS) is taken to be kPS = (qL/qM)(6/7), with 6/7 the synthesis efficiency of protein, qL the metabolizability of the diet at an arbitrary level (L) of intake and qM the metabolizability of the diet at maintenance. The correction (qL/qM) allows for the usual evaluation of ruminant diets at the maintenance level of intake. The synthesis efficiency of fat from fermentation of digestible fibre is kFF = 1.018qM or kFF = 1.287kg, without the necessity of adjustment by qL/qM, since evaluation of metabolizability at maintenance is incorporated in the relationship between kFF and qM and where kg denotes growth energy efficiency. Maintenance estimated from fasting heat production or intake at zero energy retention should be augmented by the cost of protein turnover from (PB/6) ÷ (qL/qM), with PB/6 = 102.7 kJ/kg (FW)0.75 per day for cattle and PB/6 = 78.1 kJ/kg (FW)0.75 per day for sheep, where PB denotes protein breakdown and FW fasted body mass. Alternatively, with knowledge of the degree of protein maturity, body protein turnover can be incorporated in a theoretically derived estimate of protein retention efficiency. The effective energy system can also be improved by employing theoretical protein retention and fat synthesis efficiencies or by equivalently replacing protein retention efficiency by protein synthesis efficiency in conjunction with the augmentation of maintenance heat production by the cost of protein turnover. A comparison between average growth energy efficiencies shows excellent agreement between estimates of the present theory and those of the UK Agricultural Research Council (ARC) and the US California Net Energy System (CNES), with degrees of maturity together with protein and fat gain ratios that seem typical of original experimental conditions. This implies that the present approach should do at least as well as the ARC or CNES, but can be expected to do better with reasonable accuracy in estimating the degree of protein maturity or maintenance augmentation and the composition of energy gain. The relationship between conventional growth energy efficiency and the synthesis efficiency of fat from digestible fibre allows the accumulated information of net energy systems to be transferable to the new methodology.en_US
dc.description.librarianam2014en_US
dc.description.urihttp://www.sasas.co.zaen_US
dc.identifier.citationRoux, CZ 2013, 'Use of theoretical efficiencies of protein and fat synthesis to calculate energy requirements for growth in ruminants', South African Journal of Animal Science, vol. 43, no. 4, pp. 435-456.en_US
dc.identifier.issn0375-1589 (print)
dc.identifier.issn222-4062 (online)
dc.identifier.other10.4314/sajas.v43i4.1
dc.identifier.urihttp://hdl.handle.net/2263/39685
dc.language.isoenen_US
dc.publisherSouth African Society for Animal Scienceen_US
dc.rightsCopyright resides with the authors in terms of the Creative Commons Attribution 2.5 South African Licence.en_US
dc.subjectProtein retention efficiencyen_US
dc.subjectFat retention efficiencyen_US
dc.subjectEnergetic efficiencyen_US
dc.subjectEnergy utilizationen_US
dc.subjectRuminantsen_US
dc.titleUse of theoretical efficiencies of protein and fat synthesis to calculate energy requirements for growth in ruminantsen_US
dc.typeArticleen_US

Files

Original bundle

Now showing 1 - 1 of 1
Loading...
Thumbnail Image
Name:
Roux_Use_2013.pdf
Size:
265.54 KB
Format:
Adobe Portable Document Format
Description:
Article

License bundle

Now showing 1 - 1 of 1
Loading...
Thumbnail Image
Name:
license.txt
Size:
1.71 KB
Format:
Item-specific license agreed upon to submission
Description: