1. Six wether sheep were each provided with a permanent cannula in the rumen and re-entrant cannulas in the proximal duodenum.2. In a preliminary study, the sheep consumed 200 g hay and 400 g concentrates supplemented with up to 40 g linseed oil, coconut oil or cod-liver oil daily. Feed was refused at higher levels of supplementation.3. Five of the sheep were used in a 5 x 5 Latin-square experiment. They were given 200g hay and 4OOg concentrates alone (B) or supplemented with 40 g linseed oil (L), coconut oil (C), protected linseed oil or protected coconut oil daily. The protected oils were prepared by emulsifying the free oils with formaldehyde-treated sodium caseinate. Formaldehyde-treated sodium caseinate was also included in the other three diets.4. Digestion in the stomach was measured by spot sampling duodenal digesta, using chromic oxide-impregnated paper as the marker. Microbial flow at the duodenum was measured by use of both diaminopimelic acid (DAPA) and RNA as microbial markers.5. Both the free oils had broadly similar effects despite their very different fatty acid compositions. Digestion in the stomach of organic matter (OM) was reduced from 0.48 (diet B) to 0.29 (diets L and C) and that of neutral-detergent fibre from 0.50 (diet B) to 0.19 (diet L) and 0.12 (diet C). The molar proportions of acetic acid and n-butyric acid were decreased and that of propionic acid was increased. Protozoal numbers were reduced by 78% (diet L) and 90% (diet C). The flow of total nitrogen and microbial N was increased by both oils and the efficiency of microbial protein synthesis (g N/kg OM apparently digested in the rumen) was increased from 30 (diet B) to 85 (diet L) and 74 (diet C) when based on DAPA and from 41 (diet B) to 94 (diet L) and 81 (diet C) when based on RNA. The efficiency when based on true digestion of OM (g N/kg OM truly digested in the rumen) was increased from 23 (diet B) to 46 (diet L) and 44 (diet C) when based on DAPA and from 29 (diet B) to 49 (diet L) and 46 (diet C) when based on RNA. The amounts of microbial OM (g/d) at the duodenum were increased from 68 (diet B) to 124 (diet L) and 106 (diet C) when based on DAPA and from 92 (diet B) to 136 (diet L) and 115 (diet C, non-significant) when based on RNA.6. When the oils were given in the protected form, the effects on digestion in the stomach were reduced but not eliminated. No significant increases in the amount of total N or microbial N at the duodenum were established, though there was a tendency for an increase in the efficiency of microbial protein synthesis with protected linseed oil. The results suggested that the method of protection used reduced the effects of the oils on rumen digestion and synthesis but was only partially successful in preventing hydrogenation of the fatty acids.7. It is concluded that free oils can markedly increase the efficiency of microbial protein synthesis, possibly by their defaunating effect, and that this may enhance the potential for using non-protein-N on oil-supplemented diets.

I. Sheep, cows and calves fitted with rumen cannulas were given diets mostly containing 10-16 g nitrogen/kg dry matter and consisting of roughage and cereals. Mixed bacteria w-ere separated from samples of their lumen contents.2. Bacteria taken 4-6 h after a feed from calves which were kept in an experimental calfhouse with no contact with adult animals (environment -4) contained more a-dextran, less total N and higher nucleic acid : total N ratios than similar bacteria from calves reared in contact with adult sheep (environment C ) but otherwise treated in an identical way. 3.Mixed bacteria taken 4-6 h after a feed from sheep and cows were similar in composition, with respect to nitrogenous components, to those from the 'environment C' calves. This composition did not vary significantly when diets containing differing proportions of roughage were given. 4 . The 'environment A' calves were free of ciliate protozoa. When they were placed in contact with, and were inoculated with rumen contents from, adult cattle (environment B), they rapidly developed a normal protozoal population and the chemical composition of their rumen bacteria became like that of the bacteria from the 'environment C' calves.5 . Mixed bacteria taken just before a feed, from either cows or 'environment A' calves, showed significantly lower RNA-N : total N ratios and slightly (but not usually significantly) higher DNA-N:total N ratios than bacteria taken 4-6 h after feeding. Total N contents of the bacteria did not change consistently with time after feeding.6 . The possible significance of these differences in relation to the nutrition of the host animal is discussed.The bacterial population in the rumen generally contributes a considerable part of the nutrient material entering the small intestine of the ruminant. Knowledge of the chemical composition of this population and how it varies is necessary for a proper understanding of the nutrition of the host animal and to enable calculations to be made, for example, of the contribution of bacterial protein and carbohydrate to the digesta. Results, gencrally for small numbers of samples, have been reported for total nitrogen, amino acids, nucleic acids, carbohydrates, lipids and ash as proportions of the dry matter in some samples of mixed rumen bacteria

I . Two young Friesian steers fitted with rumen cannulas were each given three different isonitrogenous and isoenergetic diets for successive periods of 2-3 weeks. The diets consisted mainly of straw and tapioca, with the nitrogen supplied mainly as decorticated groundnut meal (DCGM; diet A), in approximately equal amounts of DCGM and urea (diet B), or entirely as urea (diet C).2. At the end of each period on a given diet, part of the dietary urea of a morning feed was replaced by a solution of [lSN]urea which was infused into the rumen. Samples of rumen contents were removed just before giving the 15N dose and at I , 3 , s , 7 and 24 h afterwards, concentrations of ammonia and its I5N enrichment were determined and samples of mixed bacteria were prepared. Amino acids, ammonia derived mainly from amide groups, and hexosamines were prepared by ion-exchange chromatography of acid-hydrolysates of the bacteria and analysed for 15N.3. Approximate estimates of net bacterial N synthesis were made from turnover data for rumen fluid and I5N enrichments in rumen fractions. From the determined efficiency of incorporation of urea-N into bacteria recovered at the duodenum, it was calculated that on diets A, B and C respectively 82 x, 37 and o % of the bacterial N was derived from dietary protein or other non-urea sources.4. ['5N]urea was converted rapidly to ammonia and the 15N then incorporated into bacterial amide-N; it appeared at a slower rate in total bacterial non-amide-N. Rates of incorporation into non-amide-N were highest for glutamic acid, aspartic acid and alanine, and generally lowest for proline (pro), histidine (his), phenylalanine (phe), arginine (arg), methionine (met) and galactosamine. A similar ranking was also generally observed for relative 15N abundances (15N atoms "/, excess in N componentt15N atoms % excess in total bacterial N) achieved after several hours. Relative 15N abundances in his, arg and pro increased with decreasing protein @CGM) in the diet but those in the other protein amino acids, including the poorly labelled met, phe (and its derivative tyrosine) did not.5. It was concluded that different extents of labelling of the amino acids (at least those present mainly in protein) indicated that different amounts of preformed units (amino acids or peptides) were used. When an adequate supply of such units was available (particularly on diet A) pro, arg, his, met and phe were derived in this way to a greater extent than the other amino acids, but whereas synthesis of pro, arg and his increased on the low-protein diet C, that of met and phe did not. Thus met and phe may be limiting for bacterial growth on diets low in protein and high in non-protein-N.6. Differences in the extent of labelling of other bacteria1 N components may be due to different turnover rates.

I. The effects of various factors on rates of flow and composition of digesta leaving the abomasum of preruminant calves were studied. The possible relation of some of these effects to the development of serum antibodies to certain dietary constituents has also been examined. Two situations were distinguished : (a) unsensitized responses, shown by calves receiving milk protein or soya-bean products for the first one or two occasions; (b) sensitized responses, shown by calves receiving certain soya-bean products, after a number of these feeds had been given.2. For unsensitized calves, the rate of flow of total digesta from the abomasum was greater in the first few hours after a feed consisting of a mineral solution was given, than after cow's milk was given. This difference was apparently due to differences in the composition of digesta entering the duodenum. Total digesta flows after giving synthetic milk feeds, prepared from different protein sources, were similar to those after cow's milk was given.3. For sensitized calves, rates of flow of total digesta from the abomasum were greatly affected by the nature of the protein source used in the diet. Soya-bean flour (heated or unheated) generally caused inhibition of flow for some hours after feeding; a soya-bean protein isolate (isoelectric) had a similar but smaller effect, but a soya-bean concentrate (prepared by alcohol extraction of a soya-bean flour) and milk protein had little or no effect. The inhibition, believed to be a sign of more general disorders, appeared to be caused by a factor entering the duodenum which induced a change in the way in which the calf responded, probably as the result of a gastrointestinal allergy. 4.Calves given soya-bean flour or a soya-bean protein isolate (isoelectric) in their diets for several weeks, showed respectively high and low titres of serum antibodies to an antigen prepared from soya-bean flour. Calves given alcohol-extracted soya-bean concentrate had no similar antibodies.5. In addition to variations in total digesta flow, dietary nitrogen compounds were held up in the abomasum to different extents after different feeds. After a whole-milk feed or a synthetic feed prepared from casein, a slow, steady release of N occurred over at least 9 h. N hold-up after giving soya-bean-containing feeds was slight for the soya-bean flour, but extremely marked for the soya-bean protein isolate (isoelectric). The latter hold-up was followed after several hours by a rapid outflow of N from the abomasum.The movement of digesta from the abomasum of a calf given a feed of cow's milk is a slow, well-controlled process (Ash, 1964; Mylrea, 1966a). The rate of flow of digesta is most rapid immediately after this type of feed and decreases progressively with time, although a considerable flow continues for many hours and remains appreciable even after an 18 h fast. With increasing time the digesta contain greater proportions of materials of endogenous origin, but certain dietary constituents continue to be found for many hours. This applies ...

1. Nucleic acids introduced into the rumens of calves, or incubated with calf, sheep or cow rumen contents in vitro, were rapidly destroyed.2. The degradation products formed were separated and identified by means of column chromatography on Sephadex G-10 Dextran gel and thin-layer chromatography on cellulose.3. In vitro, RNA was rapidly (within 1 h) converted into ultrafilterable oligo-and mono-nucleotides, nucleosides, purine and pyrimidine bases. After 4 h, only the bases xanthine, hypoxanthine and uracil remained, having increased at the expense of the other constituents.4. DNA gave similar products but with a much greater proportion of ultrafilterable oligoand mono-nucleotide material which remained as a major component even after 4 h. The only bases present in appreciable amounts were thymine, hypoxanthine, uracil and xanthine.5. The same products accumulated temporarily in vivo, after addition of RNA or DNA to the rumens of calves, and were found also, in small amounts, in corresponding samples of duodenal digesta. The products disappeared from the rumen at a greater rate than could be accounted for by transfer to the duodenum.6. Cell-free preparations from calf rumen fluid contained enzymes which converted RNA and DNA into products which appeared to be ultrafilterable oligonucleotides.7. When ground hay was incubated with whole rumen contents the nucleic acids in the hay were degraded to a mixture of nucleotides, nucleosides and bases, almost as readily as were pure nucleic acids.