Factors influencing the shedding of verocytotoxin-producing Escherichia coli O157 by beef suckler cows.

A study was designed to investigate management factors that might influence the shedding of verocytotoxin-producing Escherichia coli (VTEC) O157 by beef cows in Scotland, where there is a particularly high rate of human infection. Thirty-two herds were visited at least monthly over approximately 1 year for collection of fresh faecal pat samples and information on management factors. The faecal pat samples were tested for VTEC O157 by established culture and immunomagnetic separation methods. Questionnaires were completed at the monthly visits to record management factors. Data were analysed using both univariate and multi-factor (GLMM) analysis. Changes in the number of cows in a group, dogs, wild geese, housing, and the feeding of draff (distillers' grains) were statistically significant as risk factors. The event of calving appeared to reduce the likelihood of shedding. Any effects of weaning or turnout were not statistically significant. It appears that the rate of shedding of VTEC O157 is influenced by several factors but possibly the most important of these are the circumstances of animals being housed, or, when outside, the presence of wild geese.

Long-term survival of Escherichia coli O157 on pasture following an outbreak associated with sheep at a scout camp.

AIMS: To monitor the decay of E. coli O157 in soil (loamy sand) on a scout campsite following an outbreak in humans. METHODS AND RESULTS: Samples of soil and sheep faeces were collected from the campsite and tested for the presence of E. coli O157 by immunomagnetic separation (IMS) after enrichment in buffered peptone water + vancomycin at 42 degrees C for 6 h. Enumeration of target was carried out by direct plating onto sorbitol MacConkey agar plates supplemented with cefixime and tellurite (CTSMAC) incubated at 37 degrees C for 24 h. Low numbers (< 100 g(-1)) were estimated by the most probable number (3-tube MPN) technique. CONCLUSIONS: Survival was observed for 15 weeks. SIGNIFICANCE AND IMPACT OF THE STUDY: A number of laboratory studies have followed the decay of E. coli O157 in soil, animal faeces and water. This study follows (for the first time) the decay of the organism in soil after an outbreak associated with sheep. It demonstrates the long-term persistence of the organism in the environment and the results will be potentially important in performing risk assessments for both human and animal infection.

Control of ovarian function in cattle.

In cattle, ovarian function is controlled by complex local and systemic feedback mechanisms involving gonadotrophins from the pituitary gland and steroids and proteins from the ovaries. This control system ensures that in more than 96% of females, only one follicle will ovulate per oestrous cycle. Follicular growth and development in cattle occurs in a wave-like pattern, with two or three waves of follicles growing and regressing per oestrous cycle. Each wave is characterized by the emergence, from a pool of growing follicles, of a large dominant follicle which reaches a mature stage of development and may be induced to ovulate and form a functional corpus luteum with a single treatment of either human chorionic gonadotrophin (hCG) or gonadotrophin-releasing hormone (GnRH). The growth of this dominant follicle is associated with a marked reduction in both the number and growth of subordinate follicles in both ipsi- and contralateral ovaries, suggesting a systemic exertion of 'dominance'. The dominance concept is further supported by the observation that the subsequent wave of follicular growth cannot be detected until after the start of the regression of the previous dominant follicle. Furthermore, the dominance mechanism does not involve an action of inhibin, as previously proposed. In addition, in cattle, inhibin may not have a primary role in the control of follicle-stimulating hormone (FSH) release, unlike its role in other species such as sheep. Gonadotrophins provide the primary endocrine drive for the growth of follicles > 2 mm in diameter, but it is now becoming evident that other systemic and locally produced factors profoundly influence ovarian function. For example, short-term treatment of cattle with recombinant bovine somatotropin (BST) can double the number of small (< 5 mm) antral follicles without altering the pattern of circulating gonadotrophin concentrations. These follicles appear to be fully functional since they can be stimulated to develop further and ovulate with superovulatory treatment regimens. Dominance also appears to be exerted via a different pathway from that involved in the BST-induced recruitment of small follicles. The identification of the factor responsible for dominance, together with the elucidation of the mechanisms controlling follicular recruitment and growth should ensure that the full benefits ensuing from the precise control of ovarian function in cattle are achieved.