Survival of Mycobacterium avium subsp paratuberculosis in amitraz cattle dip fluid

OBJECTIVE: To determine the survival time of Mycobacterium avium subsp paratuberculosis in amitraz-based cattle dip fluid derived from an active dip site in northern New South Wales. PROCEDURE: Following inoculation of triplicate 5 L containers with faeces (0.5 g/L) from a clinical case of bovine paratuberculosis, samples collected up to 8 weeks after inoculation were examined by conventional and radiometric culture. M a paratuberculosis colonies were enumerated on solid media. RESULTS AND CONCLUSIONS: M a paratuberculosis survived in amitraz cattle dip fluid for up to 2 weeks, but not 3 weeks. Where 1% of solids in dip fluid is derived from a clinical case of paratuberculosis, dip fluid may contain viable M a paratuberculosis for at least 2 weeks. These findings have implications for the management of cattle dip sites.     

Are pre‐spraying growing conditions a major determinant of herbicide efficacy?

To evaluate the effect of pre‐spraying growing conditions on herbicide efficacy, two years of experimentation were conducted in which Persicaria maculosa plants were exposed to different light intensities for 1–4 days before metribuzin treatment. Specific leaf area, rather than plant growth rate or plant size, was the only parameter that correlated well with herbicide efficacy in both years of experimentation. The negative relationship between the ED₅₀ and the specific leaf area indicates that leaf characteristics might be an important determinant of herbicide efficacy, for instance through an effect on herbicide uptake. In the third year of experimentation this hypothesis was further investigated by raising six cohorts of weed plants at a 1‐week interval and thus exposing them to a range of weather conditions. Clear relationships between uptake and herbicide efficacy were found for a combination of four plant species (Solanum nigrum, Senecio vulgaris, Chenopodium album and Brassica napus) and two herbicides (phenmedipham and bentazone). For phenmedipham, uptake was negatively correlated with global radiation and positively correlated with relative humidity. For the herbicide bentazone the opposite was found. These results were not species‐specific. This study shows the importance of the sensitivity of herbicide × species combinations and indicates that pre‐spraying weather information is relevant for the development of reduced dose rate recommendations.     

Alternative antimicrobial agents in the treatment of proliferative enteropathy in horses

Seven young horses 5 to 12 months old, each diagnosed with proliferative enteropathy, were studied. All seven cases responded to alternative antimicrobial therapy to the traditional treatment of erythromycin ± rifampin. Three cases were treated with chloramphenicol, two cases with doxycycline, one with azithromycin, and one with clarithromycin and rifampin. All showed resolution of clinical and clinicopathological abnormalities within 8 weeks of initiation of treatment. Proliferative enteropathy is an increasingly recognized malabsorptive and maldigestive disease of young horses. Supportive care and antimicrobial therapy are the mainstays of therapy with erythromycin being the traditional antibiotic of choice. The knowledge that alternative therapeutic antimicrobials are clinically efficacious in the treatment of Lawsonia intracellularis broadens the therapeutic options for this potentially fatal condition.     

Association of Fertility with Numbers of Antral Follicles within a Follicular Wave During the Oestrous Cycle in Beef Cattle

The association between conception rate at first service and numbers of follicles developed during a follicular wave was examined in 102 suckled beef cows and 14 heifers. Follicular development was monitored using ultrasonography for either two (trial 1) or three (trial 2) consecutive oestrous cycles (pre-breeding, breeding and post-breeding equivalent). Animals were examined on alternate days from day 6 after first oestrus (day 0) until ovulation and from day 6 after insemination until next ovulation or day 24 of pregnancy and were observed for oestrus twice daily and inseminated artificially at either the second (trial 1) or third oestrus (trial 2). Cows were classified as having two or three waves of follicular development for each oestrous cycle. Numbers of follicles >or=4 mm per wave were determined, and based on the maximum diameter they attained, were classified as small (4-6 mm), medium (7-10 mm) or large (>or=11 mm) follicles. Total numbers of follicles, and primarily numbers of small and medium follicles, were affected by trial and within trial by cow, oestrous cycle and follicular wave. Heifers had more small and total numbers of follicles, but fewer large follicles than cows in trial 1 (p < 0.05). The average number of antral follicles per wave in the breeding cycle or post-breeding period did not affect conception rates, which averaged 84%. Repeatability of the total numbers of antral follicles between and among oestrous cycles and follicular waves ranged from 0.01 to 0.97. In conclusion, fertility was not affected by the numbers of antral follicles >or=4 mm in diameter in a single follicular wave.     

Pasteurella multocida septicaemia in fallow deer (Dama dama)

Thirteen of 100 fallow deer, aged between 6 months and 10 years, died over a 5 week period. The deaths occurred in 2 outbreaks 3 weeks apart. Both outbreaks were preceded by at least 3 days of cold wet and windy weather, and were associated with water-logged pastures. Affected animals were usually found dead, with a frothy blood-stained nasal discharge. In the 8 deer necropsied, gross lesions included widespread subserosal petechial haemorrhages, severe pulmonary congestion and oedema with froth-filled airways, and fibrinous pneumonia and pleurisy in 4 deer. Two deer, also, had extensive subcutaneous petechial and ecchymotic haemorrhages and oedema of skeletal musculature. Histologically, the most significant lesions were present in the lungs. Moderate to severe pulmonary congestion and oedema, with fibrinous exudation into alveoli and septal oedema, were present in all deer. In some deer these changes were accompanied by a diffuse infiltration with polymorphonuclear leucocytes. Pasteurella multocida was isolated from a range of tissues from 7 of 8 deer examined. The remaining animal had been treated with antibiotics 8 hours before death. The isolates had identical polyacrylamide gel electrophoresis patterns and were of the same antigenic type-Carter group A, Heddleston type 3,4.