A serological survey for brucella antibodies has been carried out in Northern Ireland in an attempt to assess the effects of the brucellosis eradication programme in cattle which has been in progress since 1959. One thousand eight hundred and ninety four sera from blood donors, from farmer's lung tests, and from various groups occupationally exposed to cattle were examined by the serum agglutination test, the anti-human globulin (A.H.G.) (Coombs) test and the complement-fixation test.

The incidence of brucellosis in Northern Ireland is now less than it was 20 years ago, but is similar to that reported in a recent survey in England. It now appears that the principal method of transmission of brucellosis in the province is by occupational exposure rather than by drinking infected milk. Though it may be too early to make a serological assessment of the effects on human infections of brucellosis eradication in cattle, this survey provides a basis for future evaluation.

We thank Prof. O. L. Wade, Prof. P. C. Elmes and Dr W. R. Kerr for their encouragement and helpful advice; the Medical Officers of Health in Antrim, Armagh, Down and Fermanagh, Londonderry, and Tyrone, and in Belfast and Londonderry County Borough for help in obtaining blood samples; Dr M. C. Huth of the Northern Ireland Blood Transfusion Service, for sera; Dr D. W. R. Mackenzie and Miss H. E. Cairns for sera from the Mycology Diagnostic Laboratory; Dr J. H. Connolly for sera from the Virus Reference Laboratory, and for helpful advice; the farm workers and veterinary surgeons for volunteering blood samples; the technical staff of the Veterinary Research Laboratories for carrying out the tests.

A survey of evidence of rodent hantavirus infection in County Down, Northern Ireland was carried out by using immunofluorescence to detect virus antigen and antibody. Antibodies to hantavirus (R22 strain of Seoul virus and Hantaan 76–118) were found in 11/51 (21·6%) brown rats (Rattus norvegicus), 1/31 (3·2%) field mice (Apodemus sylvaticus) and 17/59 (28·8%) house mice (Mus domesticus). Seven rodents had evidence of hantavirus antigen in lung tissues. Antibody positive animals were significantly more likely to be adults than juveniles (P = 0·04) but and there was no sex difference between antibody positive and negative animals. House mice were more likely to be antibody positive if captured inside farm outbuildings (P = 0·08). Attempts to culture virus from the rodent material were unsuccessful. This work demonstrates a substantial rodent reservoir for hantavirus in Northern Ireland.

In an experiment, carried out over 3 years, two groups of dairy cows offered ad libitum access to grass silage received 8 kg/day concentrate differing only in phosphorus content (low P concentrate: 4·0–4·5 g/kg dry matter (D.M.); high P concentrate: 6·0–6·5 g/kg D.M.) during the winter feeding period of approximately 6 months. During the summer period all animals were grazed together on perennial ryegrass pastures. There were no consistent significant effects of P content on any of the variables measured. The mean calving indices were 371 (S.E. = 3·71, n = 122) and 379 (S.E. = 4·28, n = 95) days and overall conception rates were 0·70 and 0·68 for the low and high P treatments, respectively. Mean plasma P concentrations during the winter period were significantly reduced (P > 0·01 or greater) in years 2 and 3 of the study on the low P treatment. In 1 year milk yield was significantly higher (P > 0·01) on the low P treatment although the fat content was significantly reduced (P > 0·05) but these effects were not recorded in the other 2 years.

A detailed investigation was conducted to identify the main factors influencing the current poor reproductive performance in dairy herds in Northern Ireland. Nineteen herds were selected and a comprehensive database was established, comprising detailed information collected over a 2-year period. Milk progesterone monitoring (no.=1423 cows), based on twice weekly sampling, was included in this on-farm investigation. The mean interval from calving to commencement of luteal activity was 30·1 days and 13·4% (184/1378) of these cows had not commenced luteal activity by day 50 post partum. In addition, there was a high incidence of abnormal progesterone profiles: delayed ovulation type I; 15·6% (242/1388), delayed ovulation type II; 11·7% (125/965), persistent corpus luteum type I; 19·4% (212/1121) and persistent corpus luteum type II; 11·9% (70/619). Delayed commencement of luteal activity and abnormal profiles were associated with reduced fertility performance manifested as increased interval to first AI service and ultimately prolonged calving interval. Delayed commencement of luteal activity and abnormal progesterone profiles, with the exception of ‘delayed ovulation type II’ profiles, were not associated with lower conception rates. Assistance at calving was associated with delayed commencement of luteal activity. Delayed commencement of luteal activity and delayed ovulation types I and II profiles were associated with indicators of nutritional stress and poorer production performance in early lactation. Retained foetal membranes were strongly associated with prolonged luteal phases (persistent corpus luteum types I and II profiles). While hormonal therapy may prove useful in treating cows with abnormal milk progesterone profiles, the prevention and treatment of associated diseases and the implementation of good management practices are likely to be more rewarding.

San Pietro and Rittenberg (1953) reported that urea appeared to meet all the requirements of a satisfactory tracer. Urea is non toxic, not foreign to the body and it shows an even and rapid distribution throughout the total body water without any physiological effect. For these reasons in addition to its easy and accurate measurement, urea is an ideal candidate tracer to estimate empty body water in vivo. Total body water volume (urea space) can be estimated by dividing the total amount of urea infused by the increase in plasma urea concentration from prior to infusion until 12 or 30 minutes after mean infusion time. Kock and Preston (1973) reported significant relationships between urea space measurements and percentage of empty body fat and water in cattle. However, Andrew et al. (1995) using 21 Holstein cows showed that prediction of empty body water using the urea space technique only explained 31 % of the variation. The objective of this experiment was to use the urea dilution technique to estimate the body composition of lactating dairy cows and produce relationships between urea space and body fat and protein content.

In comparison to steers, bulls have produced 10% higher liveweight gain, 14% higher carcase gain and 20% more lean in the carcase. Immunological castration, which is reversible may reduce aggressive behaviour and maintain the performance advantages of bulls. Active immunization against luteinising hormone releasing hormone (LHRH) reduces testosterone production and therefore aggression in bulls. However, a controlled, predictable response to vaccination has not been achieved. Consistent immunization may be possible using a monoclonal antibody against LHRH. An anti-LHRH monoclonal antibody was developed and studies were carried out to determine the binding characteristics of the antibody and the half-life when administered to 6 post-pubertal bulls. The ability of the antibody to neutralize the bioactivity of LHRH was investigated in bulls and mice.

Recent developments in in vitro fertilization and embryo transfer technology (Lu, et al, 1987) have facilitated the production of twin, continental cross calves from the dairy herd through non-surgical embryo implantation. However, the successful exploitation of this technology in practice requires information on the effects of embryo transfer and/or twinning on animal performance and how these effects may be influenced by feeding and management factors. The objectives of this study were to examine the effects of different management and feed regimes pre- and post-calving on the performance of single- and twin-bearing cows.

Five randomized-block experiments were carried out over 2 years using British Friesian cows managed as three separate herds. The effects of offering cows different levels of concentrates, ranging from 0·8 to 7·2 kg/day, in addition to grass silage ad libitum during the winter period on reproductive performance was investigated. The effects of substituting 4 kg/day maize gluten, or 0·8 kg/day fish meal, for part or all of the standard concentrate were also examined.

Neither level of concentrates nor the inclusion of maize-gluten meal significantly affected reproductive performance even where milk production and quality was considerably influenced. The inclusion of fish meal improved conception rates to all services (0·64 v. 0·44; P < 0·05) and reduced the number of services required per conception (1·62 v. 2·31; P < 0·01).

Plasma urea levels were raised consistently by the feeding of fish meal and, with the exception of weeks 2 and 6 of lactation, by the feeding of higher levels of concentrates. From the 6th week of lactation levels of beta-hydroxybutyrate (BHB) in the blood were significantly higher in the group of cows receiving the highest level of concentrates. The BHB level at week 6 was correlated with the number of services required per conception.

A number of relationships between production factors and fertility are also presented.