Dictyocaulus viviparus in calves: effect of rotational grazing on the development of infections.

A study was made of the possibility of reducing lungworm infections in young grazing calves by rotational grazing for weekly periods on six paddocks. For this purpose three groups of four calves each were grazed on separate pastures in 1989, whereas a fourth group served as a permanently housed control group. Two groups of calves were infected experimentally with six doses of 10 larvae of Dictyocaulus viviparus during the first 3 weeks on pasture. In the third group, low natural infections with overwintered larvae occurred. One of the experimentally infected groups was rotationally grazed for weekly periods on six small plots while both other groups were set-stocked. Faecal larval counts and worm counts in tracer calves demonstrated lower lungworm infections in the rotationally grazed group than in both set-stocked groups. However, the numbers of worms found after challenge infection and subsequent necropsy were relatively high in the rotationally grazed group, indicating that development of immunity was less than in both other groups. Owing to the dry weather conditions in the summer of 1989, no serious clinical signs of husk developed in any of the three groups. These dry conditions, however, did not prevent the build-up of heavy pasture infectivity with gastrointestinal nematodes resulting in heavy worm burdens and serious clinical signs in tracer calves grazing for 4 days in August and September-October, respectively. This implies that rotational grazing did not have a clear effect on build-up of gastrointestinal nematode infections.     

Mechanism of resistance to fenarimol in Aspergillus nidulans

Mycelial uptake of [¹⁴C]fenarimol (10 μg/ml) by 20 fenarimol-resistant mutants of Aspergillus nidulans was compared with uptake by wild-type strain 003. Uptake of the fungicide during the initial 10 min of incubation was significantly lower in all mutant strains than in the wild-type strain indicating that resistance is related with reduced uptake. Upon prolonged incubation a gradual decrease of accumulated radioactivity in the wild-type strain was observed. A few mutants displayed resistance to unrelated chemicals such as p-fluorophenylalanine or d-serine; this phenomenon appeared not to be due to a decreased uptake of the corresponding natural amino acids. Incorporation of [³H]adenine and [¹⁴C]leucine by mycelium of mutant M193 was hardly inhibited after 5 hr of incubation with the fungicide, whereas a distinct effect was found with the wild-type strain. At this time also fungitoxicity to the wild-type strain became apparent. Probably, this effect is indirectly caused by inhibition of ergosterol biosynthesis. Mycelium of mutant M193 incorporated [¹⁴C]acetate slightly less effectively than the wild-type strain. After 2 hr of incubation with this radiochemical leakage of [¹⁴C]acetate metabolites from mycelium of the mutant strain was observed. This indicates that resistance might be correlated with increased excretion of fungal metabolites, which in turn may be related with reduced fitness of fenarimol-resistant mutants.     

Reticulosis of the visual system in a dog

A 7-year-old male Kerry Blue Terrier had been compensating for a visual deficit for approximately 2 months. Five days before examination, the dog had suddenly lost all vision and the pupils had become widely dilated and unresponsive to light. Ophthalmic examination revealed inflammation of the optic discs. Response to therapy was favourable but temporary.
Post mortem findings consisted of granulomatous optic neuritis, meningoencephalitis and chorioretinitis, similar to reticulosis.     

Serological characterization of strains of Moraxella bovis using double immunodiffusion.

Sera were produced in rabbits against nine Moraxella bovis strains isolated in Brazil and three in the United States. Antigens were prepared for double immunodiffusion tests by thawing concentrated suspensions of the strains. Sera were tested against homologous and heterologous antigen preparations by the double immunodiffusion method. Sera showing precipitin bands with heterologous antigens were absorbed. Antigenic differences were detected between the strains and a provisional grouping of strains of M. bovis was suggested on the basis of antigenic composition. Differences between isolates from different geographical locations were found and some strains appeared antigenically more complex than others. The relevance of this work to vaccine production was suggested.     

Long-term study of incidence and financial loss due to cattle babesiosis in an Argentinian dairy farm

The incidence and direct financial loss caused by babesiosis were evaluated in 121 Holstein Friesian female cattle that formed eight cohorts (1981–1988) of a dairy farm located approximately 24° 55′S 65° 29′W in Salta, Argentina. Female calves born in 1986 and 1987 (n=32) were vaccinated with a live Babesia vaccine at six months of age.

No cases of babesiosis occurred in the vaccinated cattle. The incidence of babesiosis in the six non-vaccinated cohorts was 23.6% (21/89). Eighteen of the cases were the result of Babesia bovis, one to Babesia bigemina and two to a mixed infection. Two cattle died of B. bovis infection in spite of drug treatment (diaminazene, 3.5 mg kg⁻¹). No disease occurred in cattle younger than seven months or older than 24 months. The number of cases according to age of cattle was: 7–9 months, 5; 10–12 months, 6; 13–24 months, 10.

Financial loss for the six cohorts that suffered clinical cases amounted to US $ 1624.6 (prices in October 1990)—62% were the result of physical losses and 38% to costs of control. A benefit-cost analysis of vaccination was carried out assuming that 95% of the mortality and morbidity losses of the six non-vaccinated cohorts was prevented after a single inculation of a live vaccine (cost of a dose plus administration was US $ 4.2. The benefit-cost ratio was 4:1 for each US dollar expended.     

Esperimenti di lotta contro due specie di Microlepidotteri

Ohne Zusammenfassung     

Relative sensitivity of a herbicide-resistant rutabaga genotype to cyanazine and metribuzin

Growth and photochemical response of triazine-susceptible and -resistant rutabaga ‘Laurentian’ genotypes to cyanazine (chloro-s-triazine) and metribuzin (methylthio-as-triazine) were evaluated. The young seedlings of the susceptible rutabaga were killed when cyanazine or metribuzin were applied either pre- or post-emergence. The triazine-resistant rutabaga, however, displayed a differential response to these herbicides. Metribuzin applied pre-emergence killed the seedlings at 0.4 kg ha^?1, and at 0.2 kg ha^?1 the growth was severely affected. Cyanazine even at higher rates applied pre- or post-emergence failed to inhibit growth in these plants.Chlorophyll fluorescence in leaf sections at the cotyledonary, 2-leaf and 4-leaf stages in the susceptible plants increased by 130 and 172% in response to 10^?5 M cyanazine and metribuzin, respectively, suggesting that Photosystem II reactions in these plants were severely impaired. In resistant plants, there was little or no leaf chlorophyll fluorescence (LCF) increase at this herbicide concentration. However, at 10^?4 M cyanazine and metribuzin, the LCF in resistant plants increased significantly and the increase was greater in response to metribuzin (86%) than to cyanazine (51%). This indicates that with these triazine-resistant genotypes, metribuzin is relatively more potent and at high rates is capable of interfering with photosynthesis.