Turnover of 13c in the plasma of colonial-type broilers^

The stable isotope technique can be used as a methodology that includes the natural variation of carbon 13 (¹³C) in the bodily tissues, in order to evaluate both feed quality and feed efficiency. This technique can be considered appropriate to evaluate the replacement of tissue carbon, since it directly provides carbon turnover information instead of tissue synthesis and breakdown rates in a separate fashion (Zuanon et al., 2007.)
Body/organ component turnover in adult animals can be measured using contrasting isotope-labeled diets (Gannes et al., 1998). After feed replacement, body/tissue isotope composition alterations depend on the speed of substitution of these constituents.
During the early broiler grow out turnover occurs rapidly, but with the time it becomes gradually slower until full tissue development is achieved, when turnover becomes null (Macari et al., 2002).
Most turnover research studies have used adult animals in an attempt to avoid growth-associated interpretation errors, since tissue mass increase is the main factor impacting carbon isotope dilution rates (i.e., isotope turnover) associated with metabolic turnover in growing animals (Zuanon et al., 2007).
The purpose of this study was to evaluate the turnover of ¹³C by replacing a feed based on grains with the ⁴C photosynthetic pathway for a feed based on grains with the ³C photosynthetic pathway in the plasma of 3 different colonial type broiler strains with genetic potential for slow, medium, and fast growth rates.

The experiment was carried out in the experimental farm, Faculty of Veterinary Medicine and Animal Husbandry, UNESP, Botucatu Campus, SP, Brazil. Nine hundred (900) one-day-old chicks of three different colonial type broiler strains with fast (Gray Master[Master Griss]), intermediate (Heavy Red [Vermelhão Pesado]), and slow (Red Label [Label Rouge]) growth potential rates were housed, under an intensive system. Birds were allocated to groups following a random block design with 6 treatments and 4 repetitions. Feed and water were provided ad libitum throughout the experimental period. Birds were the offspring of hens fed diets formulated with ⁴C photosynthesis grains. At hatch, chicks should show ¹³C isotope signals, similar to the ones in this diet. After placement, birds were fed diets containing mostly ⁴C cycle grains in order to start showing signal changes in their bodily tissues.

For the isotope analyses, 4 birds per treatment were selected at random on days 0, 1, 2, 3, 5, 8, 11, 14, and 21 of age. Plasma samples were thawed then analyzed in a liquid state, adding 0.3 μl to tin capsules for the determination of the carbon isotope ratios, using a mass spectrometer (DELTA-S, Finnigan Mat) coupled to an Element Analyzer (EA 1108 CHN), using the following equation:

Translator's Notice (T.N.: as is in the original document in Portuguese language:

where: d¹³C = relative enrichment of the ¹³C/¹²C ratio in each sample as compared to the PDB standard.

R = ¹³C/¹²C isotope ratio of both the sample and the standard.

In order to measure the carbon isotope turnover (isotope dilution) in the tissues for a given time interval by the first order exponential equation method in the Origin^® 6.0 Professional (Microcal Software, 1999), the time exponential function was used as expressed in the equation d¹³C(t) = d¹³C (f) + [d¹³C (i) - d¹³C(f)]e^-kt, where: d¹³C(t) = tissue isotope enrichment at any time (t); d¹³C(f) = tissue isotope enrichment at the equilibrium plateau, or final condition; d¹³C(i) = tissue isotope enrichment at initial condition; k = turnover constant on day^-1; t = time (days) from diet replacement.

¹³C mean life for muscle tissue in the condition of 50% of initial condition and 50% of final condition, in t = T is calculated using the equation  T = nl 2/k, where T = mean life (days); nl = niperian logarithm; k = constant turnover rate in the tissue on day^-1.

The mean d¹³C values in function of the time, mean life, and their corresponding equations for blood from the different colonial type broiler strains are shown in Figures 1, 2, and 3. Blood d¹³C result analysis for the Naked Neck (slow growth rate, T.N. we assume Red Label) chicken strain resulted in the equation d¹³C= -25.72 - 2.03 e^-0,5873t with a calculated carbon mean life of 1.42 days. For the Heavy Red (intermediate growth rate) chickens the equation obtained was: d¹³C= -25.57 - 2.80 e^-0,3532t with a calculated carbon mean life of 1.96 days. For the Gray Master (fast growth rate) chickens, the equation obtained was: d¹³C = -25.84 - 2.34 e^-0,4204t with a calculated carbon mean life of 1.64 days.

Figure 1. Carbon isotope dilution curves (mean ± standard deviation, n = 4) and mean life values (days) in the blood of Naked Neck chickens

Figure 2. Carbon isotope dilution curves (mean ± standard deviation, n = 4) and mean life values (days) in the blood of Heavy Red chickens

Figure 3. Carbon isotope dilution curves (mean ± standard deviation, n = 4) and mean life values (days) in the blood of Gray Master chickens

 

The mean life value in the Naked Neck chickens was the lowest (1.42 days), showing that this particular strain has the fastest ¹³C turnover rate, which was unexpected, since this is a slow growing strain. In the Heavy Red strain, mean life was the highest (1.96 days), with the slowest ¹³C turnover rate, representing the slowest growth rate among all 3 strains studied, opposite to our expectations since this was the intermediate growth strain. For the Master Grain chickens, mean life was intermediate (1.64 days), representing an intermediate growth rate for the 3 strains. These interesting results, in addition of showing a reversion among the 3 strains studied in terms of their growth rate, will also serve as the basis for and contribute with further studies using the stable isotope technique for traceability.

Using the stable isotope technique in animal nutrition research is an efficient tool leading to better understand animal metabolism.

Gratitude is expressed to FAPESP for financing the Subject Project No. 2008/57411-4, of which this study is a part. Also for the PhD funds granted in Process No. 2010/51717-4.

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Macari M, Furlan RL, Gonzales E, Sartori JR. 2007. Fisiologia aviária aplicada a frangos de corte. In: Crescimento e metabolismo muscular. Jaboticabal, FUNEP:UNESP :279-297.

Zuanon JAS et al. 2007. Muscle delta ¹³C change in Nile tilapia (Oreochromis niloticus) fingerlings fed on C₃ or C₄ cycle plants grain-base diets. Comparative Biochemistry and Physiology 147:761-765.