Seisoenvariasie in die aminosuursamestelling van rumenprotosoë

[摘要] English: The rumen content of sheep was fractionated and analyzed. Samples wereobtained over a year, at three week intervals, from a group of sixMerino sheep on natural veld. The rumen contents of another group receiving specified crude protein feed and kept indoors under controlledconditions, were also analyzed. Rumen samples were fractionated intoprotozoal-, bacterial-, fibrous- and soluble fractions by a procedureof centrifugation. Sampling and conditions under which the sheep werekept as well as fractionating procedures are described and discussed.The rumen samples as well as the different fractions were analyzed byvarious means to determine the effects of seasonal variation. Drymass, nitrogen (micro-Kjeldahl technique) and amino acid compositionof these fractions were determined. In some cases the total carbohydrate- and tryptophane contents were determined. Observation of thedifferent fractions by microscope was used for comparative purposes.For analytical determinations, including hydrolysis procedures, allsampLes were well mixed, homogenized where necessary, freeze-dried andpulverised to facilitate representative sampling. The amount of sampleneeded for amino acid determination was calculated from the nitrogencontent. Samples were hydrolized for 22 hours at 110 °C in constantboiling HCl under vacuum. Hydrochloric acid was removed by evaporationand freeze-drying after hydrolysis and the amino acids transferredquantitavely into buffer for analysis. Amino acid analysis were conducted on a Beckman Model 120 C amino acid analyzer according to astandardized procedure. The analysis were controlled for accuracy andvalues compensated for losses of certain amino acids caused by acidhydrolysis.According to results, the nitrogen as well as the total amino acidcontent varied with seasonal variations with minimum values at theend of the winter. Each amino acid, viewed as a percentage of thetotal amino acids in the fraction, remained constant within certainlimits over the full duration of the experiment. Certain essentialamino acids, i.e. Lys, lIe and Arg occured at comparatively higherconcentration levels in the protozoal fraction, whereas Thr, Ala, Tyrand Met were present at higher levels in the bacterial fraction ascompared to the rumen sample. Pro and His seem to be degraded to amarked extent in the rumen, whereas Asp and Glu occured at relativelyhigh concentration levels in all fractions, including the feed.The quality and composition of fodder have a marked effect upon themicroflora of the rumen. The sheep on crude protein feed displayedmuch higher levels of protozoa (dry mass) than bacteria. The oppositepattern was observed with sheep on the veld. Protozoa from sheep oncrude protein feed also had higher concentration levels of Lys, Tyr,Arg, Asp and Glu but lower ,levels of Ala and Gly. Bacterial fractionsfrom both groups showed very little difference in amino acid composition.These results seem to indicate a definite role for protozoa in therumen especially when the animal is fed a high quality fodder. In addition to preferentially supplying certain essential amino acids(protozoa used as feed) these organisms also seem to aid in the break-down of complex macromolecules present in the feed.In this respect a glycoside hydrolase, obtained from the protozoalfraction of grazing sheep, was partially purified and studied. Theenzyme was purified by ethanol fractionation as well as chromatographic procedures. The optimum pH as well as the activity towardsvarious carbohydrates was also determined. The occurence of specifichydrolases in the different micro-organisms is also affected by thefeed supplied to the animal. It seems essential that further studiesspecifically concerning the metabolic role of protozoa in the rumenshould be done.

[发布机构] University of the Free State