AGE-DEPENDENT CHANGES OF AMINO ACID CONCENTRATION IN THE BLOOD PLASMA OF EARLY-WEANED PIGLETS

Baranyiova Eva, A. Holub, S. Standara: Age-Dependent Changes of Amino Acid Concentration in the Blood Plasma of Early-Weaned Piglets. Acta vet. Bmo, 59, 1990: 121-127. Blood plasma amino acid (AA) concentration was determined in 10 Large White x Landrace piglets weaned on the 1st postnatal day onto a liquid diet prepared from Selasan, a commercial milk feed mixture. Blood samples were obtained at 6,9, 14, 17,25 and 25 d of age from the external jugular vein using catheters. During the period under study the blood plasma concentrations of some AA, namely serine, glycine, alanine, tyrosine and valine, showed a significant rapid decrease and that of glutamic acid, proline and phenylalanine a non-significant decrease, particularly between 9 and 14 d so that their contribution to total aminoplasmia, which also decreased with age, was reduced .. The concentrations of threonine, histidine, arginine, leucine, tryptophan and isoleucine, on the other hand, showed a significant increase during the same period, particularly between 9 and 14 d. No major age-dependent changes were recorded for aspartic acid, cystine and glutamine. These fluctuations in blood plasma concentration of the individual AA resulted in changes of their mutual ratios. The ratio of branched to aromatic AA (Fischer's index), e. g., increased with advancing age from 1.27 (at 6 d) to 2.97 (at 25 to 26 d), but even so remained relatively low. Since the environmental rearing conditions and the feeding regimen were the same during the whole 3-week period, the changes in the AA concentrations could result only from internal changes occurring with advancing age in the piglets themselves. Age, pig, neonatal development, liquid diet, aromatic and branched amino acids Amino acid (AA) concentrations in the blood plasma of piglets have been studied both at the -end of intra-uterine life (J efkova et a!. 1974, 1977) and in the first postnatal hours and days <Cuperlovi~ 1967, Bengtsson 1971, Chavez and Bayley 1977). Consideration has also been given to the effects of nutrition, e. g. AA composition of sows' colostrum (Cuperlovi~ 1967, Bengtsson 1972). However, data on age-dependent changes in the aminoplasmia of piglets during their following postnatal development have been scarce (Baranyiova and Holub 1989). Consequently, its interaction with various rearing practices and feeding regimens remained 1lIldisclosed. The present study was designed to provide further information along this line. S. Standara,' Arbesova 5, Bmo


Materials and Methods
Ten Large White x Landrace littermate piglets (6 males and 4 females) were removed from their clinically healthy mother, kept under conventional conditions in a large-scale production unit, at the end of the 1st day after birth and transferred to the laboratory where they were weighed and then reared individually in cages in a thermoneutral environment (Holub 1968;Kotrbacek et a1. 1979).
Their blood plasma AA concentrations were measured at 6, 9, 14, 17,25 and 26 d after birth, invariably at 7 h in the morning.The blood samples were obtained by means of catheters (Cavaf1x> Braun, GFR and Delmed I-Cath, USA) or cannulas (Chirafiex, CSFR) implanted in the external jugular vein (Nickel et aI. 1976), tunnelled under the skin and exteriorized behind the ear.The implantations were performed aseptically at least 48 h prior to blood sampling.The catheters were perfused with heparinized saline (10 U .ml-l) once daily.
Heparinized blood samples were centrifuged for 10 min at 12 000 g, frozen immediately afterwards and stored at -20°C until processing.
The AA content of the diet (Table 1) was determined after acid (LiSka 1976(LiSka , 1980) ) and alkaline hydrolysis with 4 mol.1-1 NaOH (Simova 1972) on an AAA 881 analyzer; that of the blood elasma was determined after deproteination with 5% sulphosalicylic acid on a T 339 (Mikrotechna,.CSSR) amino acid analyzer."- The relative growth of the piglets was expressed according to Brody (1945).The significance of the results was assessed by Student's t-test and their variability was expressed in terms of standard errors of the means.

Results
The largest contributions to the blood plasma AA concentration of the piglets were by glycine (12.0 to 20.9 %) and alanine (9.1 to 13.5 %) followed by proline,.serine, tyrosine, valine and lysine, each of which accounted for more than 5 per cent of the AA concentration (proline, 6.9 to 10.3 %; serine, 7.8 to 9.8 %; tyrosine, 2.8 to 9.3 %; valine, 2.3 to 8.2 %; and lysine 5.1 to 6.0 %).Thus glycine and alanine constituted as much as one third, and together with the other five AA almost two thirds to three quarters, of total aminoplasmia.The contributions by the remaining AA were smaller.
. The concentrations of the individual AA changed with age, though not in the same way.The concentrations of serine, glycine, alanine, tyrosine and valine,.e. g., were significantly lower at the end ofthe experiment than at its start; in the two last-named AA the decrease was by more than three quarters, in the remaining ones by one fifth to a half.This downward trend was most pronounced between 17 and 25 to 26 d and in the case of tyrosine also betWeen 6 and 9 d.The concentrations of some other AA, namely lysine, glutamic acid, proline, methionine and phenylalanine, also declined with age but the decrease was not significant.
Other AA, namely threonine, histidine, arginine, leucine, tryptophan and isoleucine, on the other hand, increased with age.Significant differences between the initial and final concentrations were recorded only for the two first-mentioned AA; in threonine, arginine, leucine, tryptophan and isoleucine the increase occurred between 9 and 14 d.The concentrations of threonine, histidine, arginine and leucine, however, fluctuated temporarily showing a significant fall between 14 and 17 d or between 17 and 25 to 26 d.
No major age-dependent changes were recorded for the remaining two AA, namely aspartic acid and glutamine.
These age-dependent changes also affected the mutual relations between the individual AA and their groups.For example, the ratio of branched AA (leucine + + isoleucine + valine) to aromatic AA (phenylalanine + tyrosine) (Fischer'S index) was 1.27 in the youngest piglets and then rose with advancing age, amounting to 2.97 at 25 to 26 d.

Discussion
The largest contributions to aminoplasmia in newborn piglets have been ascribed to alanine but also to glutamic acid, serine, valine (Cuperlovic 1967) or proline, lysine, leucine (Bengtsson 1971) or also to glycine and aspartic acid (Chavez and Bayley 1977).The differences between the published data are considerable.They can be accounted for by different sites of blood withdrawal: v. jugularis (Cuperlovic 1967), v. umbilicalis (Bengtsson 1971), sinus orbitalis (Chavez and Bayley 1977).
Another possible cause of the differences may be seen in various rearing and feeding practices.At first piglets suck colostrum in which proline accounts for almost one fifth of all AA, and leucine and also alanine, serine, glutamic acid and glycine each account for one tenth of all AA (Bengtsson 1972) so that these six AA make up almost three quarters of its total AA content.
Mter ingestion of colostrum by newborn piglets their blood plasma concentrations ofall AA increase (Cuperlovic 1967), after fasting for 6 to 9 h, on the other hand, the concentrations of all of them, except isoleucine, decrease, with interrelationships being demonstrated between the changes in the concentrations of individual AA; most of them were shown by threonine and leucine (Chavez and Bayley 1977).
Affected by the developmental changes are also the levels of branched (leucine, and valine) and aromatic (tyrosine and phenylalanine) AA, each of the two groups in a different way so that their ratio, Fischer's index, is shifted.As computed by us from the available data, Fischer's index in the plasma of newborn piglets reached 1.40 upon blood withdrawal from the vena jugularis (Cuperlovic 1967); 3.45, from the vena umbilicalis (Bengtsson 1971); and 1.69, from the orbital sinus (Chavez and Bayley 1977).After fasting it increased to 1.55 (Cuperlovic 1967) or to 1.56 (after 6 h) and to 2.77 (after 9h) (Chavez and Bayley 1977).In 3-day-old piglets it reached 2.92 (Bengtsson 1971).
Piglets in our experiments, however, were fed from the Ist day after birth a diet in whichl the predominant AA were glutamic acid (accounting for almost 20 %) and leucine and proline (each accounting for about 10 % of all AA).These three AA, together with aspartic acid and serine, made up more than half of the total molar AA concentration.With advancing age the aminoplasmia increased to almoslt three times the original level.In piglets over 20 kg in body mass, i. e. twice to three times {)lder than our experimental animals at the end of the experiment, the increase was still higher and rose further after fasting for 24 and 36 h, amounting to 2.68 and 3.34, respectively (Typpo et al. 1970).
The results of our experiments in piglets in the 2nd to the 4th postnatal week are in keeping with the data reported by other investigators except Bengtsson (1971).They are also in agreement with the data on AA levels in the plasma obtained by blood withdrawal from the vena portae in 8-to 10-day-old piglets suckled by the sows ad libitum; however, in the blood plasma obtained by blood withdrawal from the cranial vena cava the AA concentration was about 50 % lower (Shimada and Zimmerman 1973).
The live body mass ofthe piglets increased as described previously (Baranyio-V'a and Holub 1989).
Also the relative growth of the piglets was in keeping with the observations described in previous reports (Holub 1964ab, 1968Baranyiova and Holub 1989).
In the early postnatal period the hierarchy of physiological functions in piglets undergoes a change characterized by distinct developmental periods (H 0 1 u b 1968~ 1988) conditioned by a number of both external and internal signals.In consequence~ changes also occur in the blood plasma concentration of AA which are not only substrates of the metabolism but also integrative elements (Harper 1983).
In our experiments we studied the aminoplasmia in piglets subjected to a brutal intervention -weaning -on the 1st day after birth.Thus they were separated not only from the mother but also from one another.Afterwards the field of their external signals did not change any further.The stereotype of rearing remained the same.Nevertheless~ their aminoplasmia did undergo a change.Therefore its changes observed between 6 and 25 to 26 d could result only from internal signals.These led~ after an about one-week rise in aminoplasmia between 14 and to 26 d~ not only to its significant decrease (Baranyiova and Holub 1989) but also to a shift in the ratio of individual AA.
Concentrations of individual amino acids in the blood plasma of piglets (,umol.J-l) ±