Risk factors for subclinical hypocalcaemia, and associations between subclinical hypocalcaemia and reproductive performance, in pasture-based dairy herds in New Zealand.

AIMS To estimate the herd-level prevalence of subclinical hypocalcaemia within 3 days of calving, to determine cow and herd-level risk factors for this condition, and associations with reproductive performance, in pasture-based cows in New Zealand. METHODS Between 10 and 15 clinically healthy cows ≥3-years-old (n=1,051) were enrolled from 76 spring-calving dairy herds. Blood samples were collected from all cows on 1 or 2 days within 3 days of calving, and assayed for total concentrations of Ca in serum. Subclinical hypocalcaemia was defined as concentrations of Ca in serum ≤2.14 mmol/L, and herd-level prevalence was the percentage of sampled cows with subclinical hypocalcaemia. Breeding and pregnancy diagnosis data were obtained for each cow to calculate reproductive outcomes. Herd-level data about management practices were collected from farmers at enrolment. Associations between cow-level variables, and reproductive outcomes, and subclinical hypocalcaemia were examined using multivariable logistic regression mixed models. Associations between herd-level variables and prevalence of subclinical hypocalcaemia were examined using a multivariable linear regression model. RESULTS Mean herd-level prevalence of subclinical hypocalcaemia was 52 (95% CI=49-55)%. Risk of subclinical hypocalcaemia at the cow-level was associated with an interaction between age of cow and interval from calving to sampling (p=0.03). Increasing age of cow was associated with increased risk of subclinical hypocalcaemia, and cows sampled on the day of calving had an increased risk compared with cows sampled 1 or 2 days after calving. Increased herd-level prevalence of subclinical hypocalcaemia was associated with feeding grass silage (p=0.06) or maize silage (p=0.004), and feeding increasing amounts of elemental Mg in the form of magnesium oxide (p=0.02). The mean farmer-reported herd-level prevalence of clinical hypocalcaemia was 2.9 (95% CI=2.1-3.8)%. Subclinical hypocalcaemia was not associated with any of the reproductive outcomes measured. CONCLUSIONS AND CLINICAL RELEVANCE There was a high prevalence of subclinical hypocalcaemia in the pasture-fed, spring-calving dairy herds sampled and a large between-herd variation in prevalence. Subclinical hypocalcaemia increased with increasing age, and declined with time postpartum. Herd-level prevalence was associated with feeding grass silage and maize silage to pre-calving cows and with increasing amounts of supplemented magnesium oxide. Subclinical hypocalcaemia was not associated with reproductive outcomes.

Effect of treatment with oral Ca boluses following calving on concentrations of Ca in serum in pasture-based dairy cows.

AIMS To assess the effect of the administration of two oral Ca boluses on concentrations of total Ca, ß-hydoxybutyrate (BHB) and non-esterified fatty acids (NEFA) in serum, and urine pH, in recently calved pasture-fed dairy cows. METHODS Friesian or Friesian cross Jersey cows from one dairy farm were blocked by age and randomly assigned to no treatment (control; n=14), or treatment (n=13) with two oral Ca boluses administered approximately 12 hours apart, with the first bolus being given within 14 hours of calving. Each bolus weighed 198 g and contained 43 g of Ca; 31 g of Ca from calcium chloride and 12 g of Ca from calcium sulfate. Cows were enrolled over three calendar days, and all cows were managed in one group during the 24-hour study period. Blood samples were collected at 0, 1, 2, 4, 8, 12, 13, 14, 16, 20 and 24 hours after the initial treatment. Serum from each time point was analysed for concentrations of total Ca, and from 0, 12, and 24 hours for NEFA and BHB. Urine was collected at 0, 12 and 24 hours for pH measurement and pH was categorised as <7 or ≥7. The effect of treatment on percentage change in concentrations of Ca in serum relative to 0 hours, and concentrations of NEFA, BHB and urine pH, was examined using multivariable repeated measures mixed models with cow as a random effect. RESULTS In the final multivariable model for percentage change in concentrations of Ca, there was an interaction between time and treatment (p=0.004), with the percentage increase being higher in treatment than control cows at 1, 2, 4, 8 and 13 hours. At 12 hours, 5/13 (41%) treated cows had a urine pH <7compared to 0/12 (0%) control cows (p<0.001), and at 24 hours 13/13 (100%) treated cows had urine pH <7 compared to 0/12 (0%) control cows (p<0.001). Over the 24-hour period, mean concentrations of NEFA or BHB in serum were similar in treated and control cows (p>0.3). CONCLUSIONS AND CLINICAL RELEVANCE Oral treatment with two Ca boluses increased concentrations of total Ca in serum and decreased urine pH in pasture-fed cows. This bolus has the potential to reduce the prevalence and duration of subclinical hypocalcaemia in recently calved cows.

A malaria outbreak following a British military deployment to Sierra Leone.

OBJECTIVES: To describe a malarial outbreak amongst a British military force deployed to Sierra Leone in May 2000. METHODS: A case-control study was conducted that investigated possible risk or protective factors affecting the population. RESULTS: All bite avoidance measures (use of insecticide-treated bed nets and insecticide-treated clothes and use of thermal fogging/knockdown insecticide sprays) offered some degree of protection, although only use of clothes and nets was significant at the 5% level. Use of 3 or 4 protection measures was significantly protective, as was the cumulative protective effect when using multiple protective measures. CONCLUSION: Professionals giving travel advice must continue to advice travellers that they can significantly improve their levels of malarial protection by using multiple protection measures.

Recent trends in infectious diseases for travellers.

In the early 1970s medicine was considered to have conquered infectious diseases. The following three decades have shown this optimism to be misplaced, with both traditional infections increasing in prevalence and novel diseases appearing. Many of these diseases have become major problems in developing countries, and coupled with the exponential growth in international traffic now pose a significant risk to the traveller. The threat to the package tourist differs greatly from that to the businessman, soldier or backpacker. The latter groups may have little control over their food and water supplies and be exposed to vector-borne and zoonotic infections normally restricted to remote locations. However the package holidaymaker may be involved in mass outbreaks of food poisoning with novel pathogens or acquire unusual infections from close proximity to other tourists. All groups may be susceptible to diseases transmitted during travel, and these may be more common than is presently recognised. The common factor is that all such infections may be transported around the world within their incubation period, and that any disease can now present to any doctor. Today more than ever before it is incumbent on any practitioner to ask not only 'where have you been?' but also 'what were you doing there?'