Improvement of the nutritional quality of Egyptian and Sudanese sorghum grains by the addition of phosphates

1. Male broilers (0 to 35 d) were given foods with two types of yellow sorghum substituted for maize in isonutrient diets. Sorghum-based foods were also supplemented with extra phosphorus, to provide a total P of about 8 g/kg; the P being from either orthophosphoric acid or food grade dicalcium phosphate. 2. Both sorghums depressed growth and food:gain ratio and increased the incidence of locomotor disorder to about 0.50 (maize control = 0). Sorghum from Sudan, with higher concentrations of both tannin and phytate, caused more severe anti-nutritive effects than sorghum from Egypt. 3. Within the limits of statistical significance the growth depressing effect of sorghum was completely reversed by extra P. With the more toxic Sudanese sorghum this amelioration was numerically less than complete (growth = 0.94, maize control = 1). Locomotor disorders were also virtually, but not completely, eliminated by phosphorus treatment. 4. Treatment of sorghum by dry-mixing with dicalcium phosphate could form the basis of a simple and economic method for extending the use of high-tannin sorghum in poultry foods. The mode of action of the treatment remains to be determined.     

The determination of the methionine requirement of laying pullets by a diet dilution technique

A method for the determination of amino acid requirements of laying hens is described. This involves the dilution of a high protein “ summit” diet with an isocaloric nitrogen‐free mixture. By ensuring that the amino acid to be assayed is first‐limiting in the summit diet, the response to dilution can be interpreted as a response to a single amino acid.

The method is applied to the determination of methionine requirement and it is shown that the response to methionine obtained is virtually independent of the protein level of the diet and is not influenced by direct effects of the dilution mixture.

From the results of the present and other published experiments, the “ available “ methionine required for maximum egg yield of pullets in the early stages of lay is estimated to be 275 mg per bird per day.     

Uptake of the systemic fungicide triadimefon by clover and its effect on symbiotic nitrogen fixation

Clover is frequently grown in rotation with cereals in order to increase soil nitrogen. The systemic fungicide triadimefon, widely used against cereal pathogens, is readily taken up from soil by clover and degraded to a single major metabolite. Plant weight and symbiotic nitrogen fixation by Rhizobium trijolii are affected only by concentrations of triadimefon in soil that are much in excess of those likely to be encountered in practice. Triadimefon residues are thus unlikely to affect nitrogen fixation by clover under field conditions.     

Re-examination of inhibitor resistance conferred by Qo-site mutations in cytochrome b using yeast as a model system

Cytochrome b from yeast (Saccharomyces cerevisiae Meyer ex Hansen) provides a convenient model system for the study of Qo-site inhibitor (QoI) resistance mutations from a variety of organisms. QoI resistance mutations from fungal plant pathogens (G143A and F129L), malaria agent Plasmodium sp (Y279C/S), and Pneumocystis carinii (L275F), an opportunistic pathogenic fungus of man, were introduced into yeast cytochrome b and their effect on the binding of a variety of natural (myxothiazol and stigmatellin) and synthetic (atovaquone, azoxystrobin and pyraclostrobin) inhibitors to the bc1 complex monitored. L275S (from a myxothiazol-resistant yeast) was also re-examined. Stigmatellin binding was relatively unaffected by the introduction of these mutations. Significant increases in resistance were observed for the strobilurin-class inhibitors myxothiazol, azoxystrobin and pyraclostrobin, with the largest increase in resistance conferred by G143A. In contrast, atovaquone binding was most effected by Y279C/S and L275S. Notably, F129L, G143A and L275S had a minor effect on bc1 activity, and so are unlikely to confer significant fitness penalties in vivo. These data are discussed in the light of the atomic structures for myxothiazol- and azoxystrobin-inhibited bovine bc1 which have recently become available. We propose that QoI resistance due to G143A arises from steric hindrance between the inhibitor and cytochrome b, whereas the mechanism of resistance for the other mutations is due to an increase in binding energy between the protein and inhibitor molecule. Site-directed mutagenesis was also used to model selected regions of the mammalian Qo site in yeast cytochrome b in order to further understand the differential efficacy of these QoI in the mammalian and pathogen bc1 complexes.     

The effect of copper sulphate on performance and the structure of the gizzard in broilers

Addition of copper sulphate (about 200 mg per kg) to conventional diets produced a small, though variable, growth response and improved food conversion in broilers maintained under commercial conditions. In some experiments interactions were found between sex or coccidiostat and copper in the diet. Broilers fed on diets containing greater concentrations of copper (between 400 and 600 mg per kg) exhibited reduced growth rate and food intake. The gizzard linings of birds receiving diets containing 600 mg CuSO₄ per kg showed extensive damage. This damage was attributable to a massive increase in the shedding of the gizzard glandular cells into the koilin layer and to disruption and cessation of koilin production. Similar though less severe gizzard changes occurred in birds which received 400 mg per kg and there was a slight increase in cellular desquamation in some of the birds receiving 200 mg per kg. High concentrations of copper were found in the gizzard lining and caecal contents of birds receiving supplementary copper and there was a progressive increase in the concentration of copper in the litter on which such birds had been reared.