Seisoenvariasie in die aminosuursamestelling van rumenprotosoë

English: The rumen content of sheep was fractionated and analyzed. Samples were obtained over a year, at three week intervals, from a group of six Merino sheep on natural veld. The rumen contents of another group receiving specified crude protein feed and kept indoors under controlled conditions, were also analyzed. Rumen samples were fractionated into protozoal-, bacterial-, fibrous- and soluble fractions by a procedure of centrifugation. Sampling and conditions under which the sheep were kept as well as fractionating procedures are described and discussed. The rumen samples as well as the different fractions were analyzed by various means to determine the effects of seasonal variation. Dry mass, nitrogen (micro-Kjeldahl technique) and amino acid composition of these fractions were determined. In some cases the total carbohydrate- and tryptophane contents were determined. Observation of the different fractions by microscope was used for comparative purposes. For analytical determinations, including hydrolysis procedures, all sampLes were well mixed, homogenized where necessary, freeze-dried and pulverised to facilitate representative sampling. The amount of sample needed for amino acid determination was calculated from the nitrogen content. Samples were hydrolized for 22 hours at 110 °C in constant boiling HCl under vacuum. Hydrochloric acid was removed by evaporation and freeze-drying after hydrolysis and the amino acids transferred quantitavely into buffer for analysis. Amino acid analysis were conducted on a Beckman Model 120 C amino acid analyzer according to a standardized procedure. The analysis were controlled for accuracy and values compensated for losses of certain amino acids caused by acid hydrolysis. According to results, the nitrogen as well as the total amino acid content varied with seasonal variations with minimum values at the end of the winter. Each amino acid, viewed as a percentage of the total amino acids in the fraction, remained constant within certain limits over the full duration of the experiment. Certain essential amino acids, i.e. Lys, lIe and Arg occured at comparatively higher concentration levels in the protozoal fraction, whereas Thr, Ala, Tyr and Met were present at higher levels in the bacterial fraction as compared to the rumen sample. Pro and His seem to be degraded to a marked extent in the rumen, whereas Asp and Glu occured at relatively high concentration levels in all fractions, including the feed. The quality and composition of fodder have a marked effect upon the microflora of the rumen. The sheep on crude protein feed displayed much higher levels of protozoa (dry mass) than bacteria. The opposite pattern was observed with sheep on the veld. Protozoa from sheep on crude protein feed also had higher concentration levels of Lys, Tyr, Arg, Asp and Glu but lower ,levels of Ala and Gly. Bacterial fractions from both groups showed very little difference in amino acid composition. These results seem to indicate a definite role for protozoa in the rumen 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 protozoal fraction of grazing sheep, was partially purified and studied. The enzyme was purified by ethanol fractionation as well as chromatographic procedures. The optimum pH as well as the activity towards various carbohydrates was also determined. The occurence of specific hydrolases in the different micro-organisms is also affected by the feed supplied to the animal. It seems essential that further studies specifically concerning the metabolic role of protozoa in the rumen should be done.