No abstract

In two experiments designed to test the antiketogenic properties of propylene glycol and glycerol, concentrate mixtures containing 3, 6, or 9% propylene glycol or 3 or 6% glycerol were fed for the first 8 wk of lactation to a total of 120 cows. In the first experiment there were no significant effects (P > 0.05) of supplementation on milk yield and composition, feed intake, or energy balance. The cows fed a concentrate mixture containing 6% glycerol appeared to lose less body weight than the control cows or those fed concentrate containing either 3% glycerol or 3% propylene glycol. Cows fed the unsupplemented concentrate mixture were apparently less efficient in utilizing metabolizable energy than cows receiving either of the three supplemented rations but these differences were not significant (P > 0.05). There were no incidences of clinical ketosis and only 14 occurrences of positive ketone reactions in the milk (five on control, three on the 3% propylene glycol, four on 3% glycerol, and two on 6% glycerol). In the second experiment cows were subjected to slightly greater nutritional stress, which resulted in elevated ketone levels in 31 samples of milk from control cows, six from cows fed 3% propylene glycol, two for cows fed 6% propylene glycol, and three for cows fed 9% propylene glycol. Four cows, all on the control ration, developed clinical ketosis requiring glucose therapy. There were no consistent effects of propylene glycol on feed intake, body weight change, or efficiency of ration utilization. Propylene glycol supplementation appeared to increase milk yield at the 3 and 6% level and caused a slight decrease in milk fat and an increase in milk lactose percent.

Various soluble and insoluble proteins (6.25 mg) were incubated at 37 C with partially purified protease from Bacteroides amylophilus (156 micrograms) in 2.0 ml of .1 M potassium phosphate buffer, pH 7.6, for 2, 4, 6 and 18 hr, and the liberated amino acids were determined by the ninhydrin method. Results showed that (1) although soluble, serum albumin and ribonuclease A were resistant to hydrolysis; (2) soluble and insoluble proteins of soybean meal were hydrolyzed at almost identical rates; (3) soluble proteins from soybean meal, rapeseed meal and casein were hydrolyzed at different rates, and (4) treatment of resistant proteins (serum albumin, ribonuclease A and insoluble fish meal and rapeseed meal proteins) with mercaptoethanol in 8 M urea or oxidation with performic acid rendered these proteins susceptible to hydrolysis. It is concluded that (1) solubility or insolubility of a protein is not by itself an indication of the protein's resistance or susceptibility to hydrolysis by rumen bacterial protease; (2) structural characteristics of the properties which renders feed protein resistant to degradation is the presence of crosslinking disulfide bonds.

A 1,3-1,4-beta-D-glucanase (lichenase, 1,3-1,4-beta-D-glucan 4-glucanohydrolase, EC 3.2.1.73) from Bacteroides succinogenes cloned in Escherichia coli was purified 600-fold by chromatography on Q-Sepharose and hydroxyapatite. The cloned enzyme hydrolysed lichenin and oat beta-D-glucan but not starch, CM(carboxymethyl)-cellulose, CM-pachyman, laminarin or xylan. The enzyme had a broad pH optimum with maximum activity at approx. pH 6.0 and a temperature optimum of 50 degrees C. The pH of elution from a chromatofocusing column for the cloned enzyme was 4.7 (purified) and 4.9 (crude) compared with 4.8 for the mixed-linkage beta-D-glucanase activity in B. succinogenes. The Mr of the cloned enzyme was estimated to be 37,200 by gel filtration and 35,200 by electrophoresis. The Km values estimated for lichenin and oat beta-D-glucan were 0.35 and 0.71 mg/ml respectively. The major hydrolytic products with lichenin as substrate were a trisaccharide (82%) and a pentasaccharide (9.5%). Hydrolysis of oat beta-D-glucan yielded a trisaccharide (63.5%) and a tetrasaccharide (29.6%) as the major products. The chromatographic patterns of the products from the cloned enzyme appear to be similar to those reported for the mixed-linkage beta-D-glucanase isolated from Bacillus subtilis. The data presented illustrate the similarity in properties of the cloned mixed-linkage enzyme and the 1,3-1,4-beta-D-glucanase from B. subtilis and the similarity with the 1,4-beta-glucanase in B. succinogenes.

Mixed rumen micro-organisms, maintained in continuous culture readily incorporated labelled HCO3- and acetate into amino acids. Labelled propionate, in contrast, was utilized only for isoleucine biosynthesis, but failed to label other amino acids to any significant extent. Evidence was obtained showing that in these mixed, i.e. symbiotic, cultures foward tricarboxylic acid-cycle reactions only proceed to 2-oxoglutarate. 14C distribution in amino acids clearly shows that 2-oxoglutarate is not oxidized further by tricarboxylic acid-cycle enzymes. Instead, acetate is carboxylated to pyruvate which is then carboxylated to oxaloacetate. Oxaloacetate equilibrates with fumarate and thereby carbon atoms 1 and 4 as well as carbon atoms 2 and 3 are randomized. Evidence was also obtained for the carboxylation of propionate to 2-oxobutyrate, isovalerate to 4-methyl-2-oxopentanoate, phenylacetate and hydroxyphentlacetate to the corresponding phenyl- and hydroxyphenyl-pyruvic acids and succinate to 2-oxoglutarate. Of the amino acid precursors investigated, only 3-hydroxypyruvate, the precursor of serine, appeared to be synthesized via an oxidative step, i.e. 3-phosphoglyceric acid to 3-phosphohydroxypyruvic acid. Most 2-oxo precursors of amino acids in these organisms appear to be formed via reductive carboxylation of the precursor acid.