TWO trials were conducted to investigate the effect of pre-milking teat dipping (PMTD) on mastitis caused by environmentally associated pathogens. The first trial showed considerable variation in effect between herds, so a second, larger trial was conducted. In this second trial a comparison of the rate of clinical mastitis was made between nine matched pairs of dairy herds over 24 weeks of the winter housed period. All herds were near the national average incidence of mastitis before the trial. One member of each pair used their normal method of udder preparation throughout the trial and disinfected all teats after milking with an iodophor disinfectant. In the other nine herds the preparation of all teats, at all milkings, included dipping in a 025 % available iodine disinfectant, which was left on the teat for 30 s. Every teat was then wiped with a paper towel before cluster attachment. There was no difference in the overall rate of mastitis or the incidence of mastitis caused by any particular type or group of pathogens between the trial groups of herds. Both groups showed a reduction in mastitis compared with the previous winter. Although there were apparent benefits in some pairs of herds there was no overall benefit. In comparison with the previous winter the control herds reported a greater reduction in mastitis than the PMTD herds. The effect of trial supervision on normal practice gave a benefit which overwhelmed any effect of PMTD. There appeared to be no effect of PMTD on the total bacterial count, cell count or iodine content of bulk tank milk. There appears to be no justification for wholesale use of PMTD although most farms and risk groups could benefit from better attention to conventional mastitis control.The application of mastitis control techniques has reduced the incidence of clinical mastitis by some 75% in England and Wales over the last 20-25 years (Booth, 1988). Much of the effect has come from adoption of the five-point control plan and improvements in milking technology (Bramley & Dodd, 1984). This overall reduction in mastitis has been due to a significant reduction in the incidence of infections caused by Staphylococcus aureus, Streptococcus agalactiae and Streptococcus dysgalactiae, the principal causes of contagious mastitis. It is now generally accepted that the major problems remaining are in control of infections caused by

SummaryTeat orifice hyperkeratosis, a commonly observed condition in dairy cows, has been considered a consequence of machine milking and the degree of hyperkeratosis may be increased by a poor milking system. A fully illustrated technique is described which uses a scoring system from 0 for a perfect orifice to 5 for an orifice significantly enlarged with extensively protruding fronds of teat duct keratin. A range of scores found in 25 commercial dairy herds is presented. The scores have been averaged for each cow and the markedly skewed distribution corrected by a square root transformation. This scoring procedure allows comparative measures of hyperkeratosis within and between herds. An 8-fold difference (0·17–1·31) in herd average score was found. Within all herds the score increased with lactational age of the animals and peaked, for any lactation, some 3–4 months post partum, declining as the animals dried off. There was no significant relationship between mean somatic cell count and degree of hyperkeratosis at the herd level. This implies that such chronic pathological changes are unlikely to be related to the level of intramammary infection. It appeared that some hyperkeratosis is an obvious and probably natural response to milking and occurs in a significant proportion of animals in all herds although often only to a slight degree. Much more hyperkeratosis may be a measure of the performance and management of the herd. The genetic influence is unknown. Higher yielding cows will score higher as they milk for longer, but generally high scores may reflect consistent and possibly considerable overmilking. Hyperkeratosis may be an indicator of the quality of management and show the level of attention being paid to the welfare of the herd.

PROLIFERATIVE enteropathy (ileitis) is a common disease affecting pigs under various management systems worldwide. It is particularly noticeable in herds of high health status, affecting pigs in acute and chronic disease forms. In affected pigs six to 16 weeks old, the chronic form of the disease is evident as diarrhoea, reduction of growth rate and failure to thrive. Estimates of the reduction in weight gain and feed conversion efficiency range from 20 to 50 per cent (Rowland and Lawson 1992, Mackinnon 1993). In older pigs, affected animals show bloody scours and sudden death. The causative agent is Lawsonia intracellularis, an obligate intracellular bacterium others 1993, 1995). Culture of this organism requires specialised cell culture techniques, including microaerobic conditions and cell lysis passage techniques. Data on the likely efficacy of drugs such as tiamulin and tylosin in challenge-exposure studies in conventional pigs has also been reported recently others 1996, 1997). These studies reproduce the chronic form of the disease in recently weaned pigs, with diarrhoea and reduction in weight gain evident in challenged, unmedicated pigs.The tetracycline antibiotic chlortetracycline is widely used in the pig industry as an ingredient for in-feed medication for the prevention and treatment of diseases caused by bacteria which are sensitive to its action. Tetracyclines act by binding to bacterial ribosomes and blocking their formation and protein synthesis. The minimum inhibitory and bacteriocidal concentrations of chlortetracycline-HCl for L.intracellularis have been estimated in vitro .In this study, L intracellularis strain LR189/5/83 was isolated by co-culture in the rat enterocyte cell line IEC-18 (ATCC CRL 1589), using described methods (Lawson and others 1993). The strain was originally isolated from the intestinal lesions of acute proliferative enteropathy in a British pig. Following its initial growth after inoculation of intestinal material onto cultured cells, the bacterial strain was released from the cells by cell lysis, then passaged onto fresh cells. During its isolation the cultured strain had been tested for freedom from Chlamydia species, Mycoplasma species and other bacterial contaminants by cultural and immunological methods, using commercial reagents. Intracellular bacteria were expanded during weekly passage into large cell culture flasks. Following a total of nine passages, bacteria were harvested by collection ofbacteria within the supernatant portion of the cultures, collection ofbacteria in harvested cell lysate material and a combination of these two collection procedures. Bacteria used for inoculation of pigs were finally suspended in sucrose-potassium-glutamate buffer with 5 per cent fetal calf serum. Attempted culture of the inoculum on routine bacteriological agar and broths showed no evidence of bacterial growth after two, five or seven days. Cytospin smears of the supernatant portion of the inoculum showed numerous bacteria resembling L intracellularis evident within deta...

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