An introduced whitefly species, responsible for over a half billion dollars in damage to U.S. agricultural production in 1991, is morphologically indistinguishable from Bemisia tabaci (Gennadius). However, with the use of polymerase chain reaction-based DNA differentiation tests, allozymic frequency analyses, crossing experiments, and mating behavior studies, the introduced whitefly is found to be a distinct species. Recognition of this new species, the silverleaf whitefly, is critical in the search for management options.

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INTEREST in organic dairy farming has recently increased in both the UK and Europe due primarily to overproduction of food, public concerns about animal welfare and food safety and the environmental impact of many intensive systems of farming. Klenke (1989) compared the performance of organic and conventional dairy herds and reported both lower culling rates and a reduced incidence of lameness in the organic herds. However, maintaining the health status of the dairy herd by using preventive management rather than conventional treatments is a major challenge for dairy farmers converting to organic farming. The United Kingdom Register of Organic Food Standards (UKROFS 1993) stated that the objective of sustaining animals in good health in an organic farming system should be 'the adoption of effective management practices, including high standards for animal welfare, appropriate diets and good stockmanship rather than relying on the routine use of conventional veterinary treatments'. Currently there is little information in the literature on the effect of these management practices on the health status of organic dairy herds when alternative remedies (for example, homoeopathic) are introduced for the treatment of some ailments in place of conventional medicines (for example, antibiotics).In a two-year on-farm study from 1993 to 1995, animal health records were collected from 11 dairy herds in England and Wales that were either in the process of converting (n=8) or had recently converted (n=3) from conventional to organic dairy farming. The main objectives were to monitor the overall health status of the dairy herds and to identify any specific problems associated with the conversion to organic farming. All health events that occurred and treatments used for specific ailments were recorded by the herdsmen, including visits by the local veterinary surgeon. The data were collected from the farms every three months. The size of the herds ranged from 42 to 303 cows (mean, 106 cows per herd), with all herds fed diets formulated with a high proportion of home-grown forage. With the exception of one herd of Ayrshire cattle, the breed of cows was predominantly Holstein Friesian. The majority of herds had an all-the-year calving pattern with winter housing in either strawbedded cubicles (n=7) or covered yards (n=4).All the farms started using some alternative remedies (for example, homoeopathic, herbal) for the treatment of specific ailments prior to the start of the study. Seven of the farms added a nosode to the drinking water specifically for preventing mastitis. In addition to the use of alternative remedies and antibiotics, four farms used a combination of manually massaging the udder and the frequent application of cold water for treating cases of clinical mastitis. The routine use of long-acting antibiotics during the dry period ceased on the farms prior to the start of the study.On all the farms milk samples were taken monthly from the bulk tank to determine both the total bacterial count (TBC) and the level of somati...

Changes in the crude protein (CP) concentration of white clover and perennial ryegrass herbage from a mixed sward were determined on six sampling dates from May to October in each of 2 years. The swards were grown without fertilizer N in an organic farming system and continuously grazed by dairy cows during the grazing season. The annual mean contents of white clover in the dry matter (DM) of the sward were 272·3 and 307·0 g kg−1 in Years 1 and 2. The mean CP concentrations of the white clover and perennial ryegrass herbage were 251·6 and 151·9 g kg−1 DM in Year 1 and 271·9 and 174·0 g kg−1 DM in Year 2 respectively. The CP concentration of the white clover increased significantly during the grazing season from 220·0 to 284·1 g kg−1 DM in Year 1 and from 269·0 to 315·5 g kg−1 DM in Year 2. In the perennial ryegrass herbage the CP concentration increased from 112·2 to 172·6 g kg−1 DM in Year 1 and from 142·7 to 239·5 g kg−1 DM in Year 2. The rate of increase during the season in the CP concentration of the perennial ryegrass herbage was similar to the rate of increase recorded in the white clover herbage.

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