Formulated in terms of protein synthesis (PS) and protein retention (PR), a definition of turnover-related protein retention efficiency (k P ) allows the expression k P ¼ ½1 þ ðPS=PRÞ=6 21 , 6 representing the ratio of the energy equivalent of protein to the cost of synthesis. By combining plausible hormonal and cellular control mechanisms of protein (P) growth, it is possible to derive ðPS=PRÞ ¼ ½Q{ðP=aÞ 2ð4=9ÞY 2 1} 21 þ 1, allowing the calculation of k P by substitution. The symbol a represents the limit value of protein growth, while the term 4/9 derives from the power in the relationship between the concentration of growth factor-related activator in the nucleus and cell volume (cv). Y is the power in the relationship between cv and total tissue protein, and Q represents the proportion of growth factor-activated nuclei in a tissue. The proportion Q can be estimated from simple functions of intake rates or blood growth factor concentrations. Estimates of Y are derived from histological considerations or calculated from experimental observations; Y ¼ 1 for multinucleated skeletal muscle fibres and Y ¼ 1/3, 1/2, 1/6 on average for mononucleated cell tissues, skin or bone and viscera, respectively. To apply k P to the whole body, an average value of Y ¼ 1/2 can be taken. Experimental observations on tissue protein synthesis and breakdown rates yield direct estimates of k P in satisfactory agreement with comparable theoretical predictions. Protein turnover: Protein retention efficiency: Body tissuesBergen and Merkel (1991) suggested that the discrepancy between regression estimates of protein retention (PR) efficiency and theoretical estimates of synthesis efficiency indicated a major contribution ascribable to protein turnover in the generally accepted estimates. Quantification by Roux (2005a,b) has shown that this is indeed the situation for whole-body PR efficiency in pigs, cattle and sheep.Theoretical values for the parameters in Roux (2005a) were derived using the assumption that heart values are representative of average values for the whole body. It was shown that the difference between protein synthesis and breakdown related to body protein according to the relationship between nuclear and tissue sizes during growth. It follows that ideas used in whole-body and heart scaling by Roux (2005a) can be extended to accommodate different aggregates of body tissues. In addition, two improved derivations are given in this paper. First, previously neglected ribosomal scaling (Roux, 2005a) is accommodated. Second, an exact estimate of k P is derived and compared with the previous approximation (Roux, 2005a), necessary for application in conjunction with established equations for growth description in the literature.From a nutritional standpoint, differences in PR efficiency between tissues are important in two ways. The first is for predicting nutrient requirements for growth in different tissues from turnover-related efficiencies; the second is for estimating the contributions to maintenance from protein turnov...

NAUDÉ, T.W., BOTHA, C.J., VORSTER, J.H., ROUX, C., VAN DER LINDE, E.J., VAN DER WALT, S.I., ROTTINGHAUS, G.E., VAN JAARSVELD, L. & LAWRENCE, A.N. 2005. Claviceps cyperi, a new cause of severe ergotism in dairy cattle consuming maize silage and teff hay contaminated with ergotised Cyperus esculentus (nut sedge) on the Highveld of South Africa. Onderstepoort Journal of Veterinary Research, During December/January 1996/97 typical summer syndrome (hyperthermia and a 30 % drop in milk yield) occurred in succession in two Holstein dairy herds (n = 240 and n = 150 milking cows, respectively) on the South African Highveld. These farms are situated in the midst of the prime maize and dairy farming areas of South Africa where this condition had never been diagnosed before.The individual components of the concentrate on both farms were negative for ergot alkaloids. Endophytic fungi and/or ergot infestation of teff and other grasses fed to the cows were then suspected of being involved, but neither endophytes nor ergot alkaloids could be implicated from these sources.By measuring the serum prolactin levels of groups of sheep (n = 5) fed the first farm's total mixed ration (TMR) or its three individual fibre components for a period of 11 days, the source of the ergot alkaloids was identified. A statistically significant decrease in the level of this hormone occurred only in the group on maize silage (which constituted 28 % on dry matter base of the TMR). The involvement of the maize silage was further chemically confirmed by the high levels of total ergot alkaloids, predominantly ergocryptine, found by LC-MS in the silage as well as in the TMR (115-975 ppb and 65-300 ppb, respectively). The ergot alkaloid content (mainly ergocryptine) of the maize silage on the second affected farm was 875 ppb. Withdrawal of contaminated silage resulted in gradual recovery of stock on both farms.Nut sedge (Cyperus esculentus and Cyperus rotundus of the family Cyperaceae) has a world-wide distribution and is a common weed in annual crops, and can be parasitized by Claviceps cyperi. Careful examination of the maize silage from both farms revealed that it was heavily contaminated 1 Division of Toxicology, ARC-Onderstepoort Veterinary Institute, Private Bag X05,

From the observation that fasting heat production includes the cost of body protein resynthesis and the evidence that protein resynthesis is included in the regression estimate of protein retention efficiency it is conjectured that the estimate of maintenance from fasting heat production must be conceptually equal to the regression intercept estimate of maintenance plus the cost of body protein resynthesis. Experimental evidence for comparable situations shows an approximate observational equality in agreement with the conjectured conceptual equality. This approximate equality implies that the theoretical (stiochiometric) efficiency of protein synthesis should be used in conjunction with the estimate of maintenance from fasting heat production for the prediction of growth energy requirements. The approximate maintenance equalities suggest furthermore approximate equality of theoretical fat synthesis efficiency and regression fat retention efficiency. This conjecture is also supported by experimental evidence. Some practical nutrition and pig breeding implications of the foregoing conclusions are indicated. Estimation of energy requirements: Estimation of maintenance: Fasting heat productionThe factorial model proposed by Kielanowski (1) describes metabolisable energy (ME) utilisation as the sum of three factors, namely maintenance, the total cost of protein retention (PR) and the total cost of fat retention (FR). It follows that in a regression context maintenance can be estimated by the intercept (INT) in the simple regression relationship between ME intake (MEI) and energy retention (ER) or the INT in the multiple regression relationship between MEI and both PR and FR. As energy balance does not necessarily imply both protein and fat balance (2) , these INT are not necessarily identical. However, estimates of the two possible INT may not differ much, as indicated by a comparison between regression estimates from Tables 1.11 and 1.12 by the Agricultural Research Council (ARC) (2) .A third possibility for the estimation of maintenance is from a measurement of fasting heat production (HP), scaled by the efficiency of the utilisation of ME below maintenance. It is the purpose of the present paper to show that INT estimates of maintenance agree with fasting HP estimates if they are supplemented with estimates of the cost of body protein resynthesis. This finding is in agreement with the hypothesis that the ordinary regression estimate of PR efficiency (k P ) is deflated by the effects of body protein resynthesis. It also implies that the fasting HP estimate of maintenance should be used in conjunction with the theoretical (stoichiometric) efficiency of protein synthesis (PS).From the foregoing approximate equalities one would expect that regression estimates of FR efficiency (k F ) should be approximately equal to theoretical estimates of fat synthesis efficiency. Experimental evidence confirms this conjecture. Theory and methods Turnover-related protein retention efficiencyTaking turnover into account, k P can be ...

In pigs the quantification of breakdown and synthesis by powers of body protein led to the estimation of turn-over related protein retention efficiency by the equation kP= {1 + [1 − (P/α)(2/9)Q]−1/6}−1, with α the limit value of whole body protein (P) maturity, so that 0 ≤(P/α)≤1. The factor 2/9 is derived from diffusion attributes indicated by cell and nucleus geometries α and Q represents a scaled transformation of intake, 0 ≤ Q ≤ 1, such that a value of Q = 1 may represent ad libitum intake and Q = 0 the intake at the maintenance requirement. Published observations on finishing steers provide estimates of whole body protein synthesis and breakdown at pre-determined levels of intake in confirmation of the theoretical (2/9)Q power associated with (P/α) inkP. Further confirmation of the (2/9)Q power in cattle follows from satisfactory agreement between an estimate of conventional multiple regression retention efficiency and the turn-over related retention efficiency calculated at the given level of intake, for the mid point of the body mass interval covered by the regression estimate. In addition, a simulation experiment on cattle from the literature gives power estimates of protein breakdown and synthesis in general agreement with those accepted for pigs. Examples on both fine and coarse diets are employed to suggest a general rule for prediction on diets causing submaximal efficiency due to suboptimal intakes.In sheep, evidence derived from estimates of conventional multiple regression efficiencies suggests that the rule (a-b) = (2/9) Q for the calculation ofkPshould be reserved for the description of compensatory growth. Protein retention efficiency for ordinary growth should be described by an adaptation of the rule derived for suboptimal intakes.

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