The production system and disease incidence in a national random longitudinal study of Swiss dairy herds

Invited review: Opportunities for genetic improvement of metabolic diseases

Metabolic disorders are disturbances to one or more of the metabolic processes in dairy cattle. Dysfunction of any of these processes is associated with the manifestation of metabolic diseases or disorders. In this review, data recording, incidences, genetic parameters, predictors, and status of genetic evaluations were examined for (1) ketosis, (2) displaced abomasum, (3) milk fever, and (4) tetany, as these are the most prevalent metabolic diseases where published genetic parameters are available. The reported incidences of clinical cases of metabolic disorders are generally low (less than 10% of cows are recorded as having a metabolic disease per herd per year or parity/lactation). Heritability estimates are also low and are typically less than 5%. Genetic correlations between metabolic traits are mainly positive, indicating that selection to improve one of these diseases is likely to have a positive effect on the others. Furthermore, there may also be opportunities to select for general disease resistance in terms of metabolic stability. Although there is inconsistency in published genetic correlation estimates between milk yield and metabolic traits, selection for milk yield may be expected to lead to a deterioration in metabolic disorders. Under-recording and difficulty in diagnosing subclinical cases are among the reasons why interest is growing in using easily measurable predictors of metabolic diseases, either recorded on-farm by using sensors and milk tests or off-farm using data collected from routine milk recording. Some countries have already initiated genetic evaluations of metabolic disease traits and currently most of these use clinical observations of disease. However, there are opportunities to use clinical diseases in addition to predictor traits and genomic information to strengthen genetic evaluations for metabolic health in the future.

Integrating novel data streams to support biosurveillance in commercial livestock production systems in developed countries: challenges and opportunities

Reducing the burden of emerging and endemic infectious diseases on commercial livestock production systems will require the development of innovative technology platforms that enable information from diverse animal health resources to be collected, analyzed, and communicated in near real-time. In this paper, we review recent initiatives to leverage data routinely observed by farmers, production managers, veterinary practitioners, diagnostic laboratories, regulatory officials, and slaughterhouse inspectors for disease surveillance purposes. The most commonly identified challenges were (1) the lack of standardized systems for recording essential data elements within and between surveillance data streams, (2) the additional time required to collect data elements that are not routinely recorded by participants, (3) the concern over the sharing and use of business sensitive information with regulatory authorities and other data analysts, (4) the difficulty in developing sustainable incentives to maintain long-term program participation, and (5) the limitations in current methods for analyzing and reporting animal health information in a manner that facilitates actionable response. With the significant recent advances in information science, there are many opportunities to develop more sophisticated systems that meet national disease surveillance objectives, while still providing participants with valuable tools and feedback to manage routine animal health concerns.

Calf health monitoring in Norwegian dairy herds

The aims of this study were to estimate the incidence of calf diseases in Norwegian dairy herds, improve calf health recordings in the Norwegian Cattle Health Recording System (NCHRS), and investigate different methods for validation of calf health data. A longitudinal, cross-sectional survey of calf health in Norway was performed between September 1, 2004, and January 31, 2007. The participating dairy herds were randomly selected from among herds registered in the Norwegian Dairy Herd Recording System as having at least 15 cow-years. Each herd participated for 1 yr. Diseases and treatments of calves of up to 180 d of age in 135 dairy herds were reported using the NCHRS. In total, 6,668 calves were born in the participating dairy herds during the project period. A total of 573 (29.6%) of the 1,936 calf health recordings reported were recordings of diseases and 1,363 (70.4%) were events of preventive therapy, dehorning, or castration. The recorded incidence of diarrhea and respiratory disease was 3.8% and 2.9%, respectively. The median age of occurrence of diarrhea and respiratory disease was 17 and 37 d, respectively. Three different methods, based on sampling of diseased calves, dehorning as an indicator of a well-functioning recording system, or feedback on degree of commitment to calf health recording, were tested to assess validation of the calf health records. The 3 methods indicated an underestimation of calf health records in the NCHRS of approximately 40% and an estimated "true" incidence of diarrhea and respiratory disease of 5.5 and 4.1%, respectively. The results from this study demonstrate the importance of encouraging farmers to conduct calf health recordings. They also indicate that finding a standardized method for validation of health data is a considerable challenge.

Data quality of animal health records on Swiss dairy farms

High-quality data are essential for veterinary surveillance systems, and their quality can be affected by the source and the method of collection. Data recorded on farms could provide detailed information about the health of a population of animals, but the accuracy of the data recorded by farmers is uncertain. The aims of this study were to evaluate the quality of the data on animal health recorded on 97 Swiss dairy farms, to compare the quality of the data obtained by different recording systems, and to obtain baseline data on the health of the animals on the 97 farms. Data on animal health were collected from the farms for a year. Their quality was evaluated by assessing the completeness and accuracy of the recorded information, and by comparing farmers' and veterinarians' records. The quality of the data provided by the farmers was satisfactory, although electronic recording systems made it easier to trace the animals treated. The farmers tended to record more health-related events than the veterinarians, although this varied with the event considered, and some events were recorded only by the veterinarians. The farmers' attitude towards data collection was positive. Factors such as motivation, feedback, training, and simplicity and standardisation of data collection were important because they influenced the quality of the data.

Why is it getting more difficult to successfully artificially inseminate dairy cows?

Successfully using artificial insemination (AI) is defined as getting cows pregnant when the farmer wants them in-calf and making the best use of appropriate genetic potential. Over the past 30 to 50 years, the percentage of animals in oestrus that stand-to-be-mounted (STBM) has declined from 80% to 50%, and the duration of STBM from 15 h to 5 h; both in parallel with a reduction in first-service-pregnancy-rate from 70% to 40%. Meanwhile, the incidence of lameness and mastitis has not decreased; and it takes more than an extra 40 and 18 days, respectively, to get a lame or mastitic cow in-calf compared to healthy herd-mates. The intensity of oestrus is 50% lower in severely lame cows, and fewer lame cows ovulate. Luteal phase milk progesterone concentrations are also 50% lower in lame cows, and follicular phase oestradiol is also lower in non-ovulating lame cows compared to ovulating animals. Furthermore, lame cows that do not ovulate do not have an LH surge, and the LH pulse frequency in their late follicular phase is lower (0.53 v. 0.76 pulses/h). Thus, we suggest that the stress of lameness reduces LH pulsatility required to drive oestradiol production by the dominant follicle. The consequent low oestradiol results in less-intense oestrus behaviour and failure to initiate an LH surge; hence there is no ovulation. A series of experimental studies substantiate our hypothesis that events activating the hypothalamus-pituitary-adrenal axis interfere at both the hypothalamus and the pituitary level to disrupt LH and oestradiol secretion, and thus the expression of oestrus behaviour. Our inability to keep stress at a minimum by appropriately feeding and housing high-production cows is leading to a failure to meet genetic potential for yield and fertility. We must provide realistic solutions soon, if we want to successfully use AI to maintain a sustainable dairy industry for the future.

Age–period–cohort analysis of the Bovine Spongiform Encephalopathy (BSE) epidemic in Switzerland

Cattle born after animal-feed control measures were implemented in 1990 have become BSE cases in Switzerland, indicating sub-optimal effectiveness of these measures. To evaluate these measures, the incidence of BSE cases in Switzerland recorded through clinical case reporting from January 1991 to June 2000 (categorized into age groups and birth cohorts of 6-month duration) was analyzed by Poisson log-linear regression using an age-period-cohort model. The incidence was maximum in the cattle cohort born from October 1989 to March 1990, and dropped to zero in the cohort born from April to September 1991. A second peak was observed in a cohort born from April to September 1994. The first drop of incidence is interpreted as a result of initial implementation of the feed ban in 1990. The second peak might be related to exposure of cattle to feed intended for pigs and poultry.

Use of listeriolysin O and internalin A in a seroepidemiological study of listeriosis in Swiss dairy cows

Recombinant listeriolysin O and internalin A were used as antigens in an enzyme-linked immunosorbent assay (ELISA) for the specific detection of anti-Listeria monocytogenes antibodies in cattle. The results showed sensitivities and specificities of 82 and 92%, respectively, for the listeriolysin O ELISA, and 100 and 90%, respectively, for the internalin A ELISA, respectively. The test may be useful for the confirmation of listeria-related abortions and mastitis but does not seem to be indicated for use in the diagnosis of listeria-related encephalitis in cattle. A representative sample of 1,652 serum samples from the healthy dairy cattle population in Switzerland was tested by both ELISAs. The results showed that 11% of the healthy dairy cows in Switzerland simultaneously presented antibodies toward listeriolysin O and internalin A, and 48% of the farms had one or several animals simultaneously positive by assays with both antigens. Multivariable analysis at the farm level confirmed that feeding of silage represents a significant risk factor for a positive listeria serology. Detailed analysis identified corn silage but not grass silage as the major factor in this association. Cattle breed and hygiene on the farm were also identified as significant factors associated with the serological status of farms. In conclusion, the results of the study show that internalin A is a promising new antigen for use in listeria serology and that specific anti-L. monocytogenes antibodies are found in a significant proportion of healthy dairy cows in Switzerland.

Investigation of mastitis problems on farms

The production of high-quality milk is a high-priority issue for dairy farmers and milk processors. The investigation of mastitis problems on dairy farms is an area of increasing demand and is an ideal way for veterinary practitioners to increase involvement in production medicine programs. Goals for the amount of clinical and subclinical mastitis should be predefined on dairy farms, and a herd investigation initiated when needed. The use of a structured approach to mastitis problems can identify risk factors for infection, result in rapid resolution of mastitis problems, and hasten the application of appropriate preventive practices.

Clinical bovine mastitis in Norway

A brief description of the Norwegian Health Card System for Cattle (NHCSC) is given. The incidence of clinical mastitis (CM) for dairy cows in Norway was determined using NHCSC data recorded from 1992 to 1995. Incidence density (ID) (which included repeated episodes of CM in the same cow) and various measures of risk were estimated. The ID for the entire study period, comprising almost 1.2 million cow-years, was 49 CM episodes per 100 cow-years at risk. Twenty-six percent of the cows with CM experienced at least two episodes of CM in 1 year. For the entire study period (1992-1995), the ID was 30 episodes per 100 cow-years at risk for acute CM (ACM). Annual risk of CM for fixed cohorts of cows that were at risk 1 January the particular year, as estimated by the actuarial method and accounting for the exact time of removal of culled cows, varied between 0.32 (1992) and 0.35 (1994 and 1995). Numerically similar risk estimates were found when using the density method for fixed cohorts. Lactational incidence risk for cows that calved in 1992-1994 varied between 0.32 and 0.34. In herds of a size greater than five cow-years, the crude ID of CM tended to decrease with increasing herd size. The ID of CM varied considerably between counties, and was higher in coastal areas than in inland areas.

Establishment and maintenance of a longitudinal study of bovine spongiform encephalopathy (the ULiSES scheme)

This paper addresses the issues of tracing and compliance encountered in setting up and maintaining a UK-wide 5-year observational study of beef cattle. The 5-year prospective study was initiated in 1997 to investigate the occurrence of bovine spongiform encephalopathy (BSE) in a single herd of pedigree Aberdeen Angus cattle, in which BSE had been detected at low prevalence. The study was given the acronym ULiSES (University of Liverpool Spongiform Encephalopathy Scheme). All cattle present on the farm at the start of the scheme were registered as members of the study population (n=320), as were all calves subsequently born on the farm (n=350). Animals that were sold (n=291) were traced and monitored at destination farms. Farmers were requested to give advance notification of slaughter of any ULiSES animal and an attempt was made to collect post-mortem samples of nervous tissue, peripheral lymphoid tissue and striated muscle from all animals in the scheme at the time of slaughter, death or euthanasia. Sections of medulla were examined (by standard histopathological techniques) for the presence of spongiform change. Remaining samples were stored at -70 degrees C for future investigation by alternative tests. At the halfway point of the scheme in October 1999, 75.2% (506/673) of the study population was still alive; 42% (284) of the population was still alive on the study farm and 33% (222) was distributed on other farms throughout the UK. Complete sets of specimens had been recovered from 77% (129/167) of dead animals. All brainstem sections were negative by histopathological examination. No suspect cases of BSE were reported in ULiSES animals. Failure to recover specimens occurred principally in animals which had left the study farm. The main cause of specimen loss was a failure of compliance in a small number of individuals who had purchased large numbers of ULiSES animals, and subsequently slaughtered them without contacting the University. Despite this, farmer compliance was generally high. The ULiSES scheme shows the feasibility of a country-wide longitudinal observational study spanning a period of several years and indicates the large impact of small numbers of non-compliant individuals.

Disease incidence in dairy herds in the southern highlands district of New South Wales, Australia

The purpose of this study was to determine clinical disease incidence in eight non-seasonally calving, pasture-fed dairy herds in the southern highlands district of New South Wales. This was a longitudinal population study. The study included all cows that calved between January 1994 and December 1995 and consisted of 2111 lactation records from 1430 cows. The incidence of the more common diseases were: calving-associated disorders, 18.0 cases per 100 calvings (95% CI 16.4-19.8 cases per 100 calvings); metabolic disorders, 5.5 cases per 100 cow-yr at risk (95% CI 4.5-6.6 cases per 100 cow-yr at risk); reproductive-tract disorders, 22.3 cases per 100 cow-yr at risk (95% CI 19.2-25.8 cases per 100 cow-yr at risk); udder disorders, 17.6 cases per 100 cow-yr at risk (95% CI 15.9-19.5 cow-yr at risk) and lameness, 3.7 cases per 100 cow-yr at risk (95% CI 2.9-4.7 cow-yr at risk). In agreement with dairy-cow disease-incidence studies conducted elsewhere, disorders of the reproductive-tract and udder were the most frequent clinical conditions encountered. These findings confirm that dairy herd-health programs should emphasise the control of these two groups of disorders.

Modelling the expected numbers of preclinical and clinical cases of bovine spongiform encephalopathy in Switzerland

The objective of this study was to model the expected numbers of cattle incubating bovine spongiform encephalopathy (BSE) and the numbers of clinical cases of BSE in the Swiss cattle population between 1984 and 2005. The results were compared with the observed number of clinical BSE cases and with the results of a culling and testing scheme on herdmates of cattle with BSE. The age distribution of the Swiss cattle population, the age-at-death distribution of the first 235 BSE cases and exposure information were used to calculate the expected number of infected cattle in each birth cohort and the resulting numbers of clinical cases and survivors incubating the disease for each year. The model which did not assume any under-reporting of cases fitted the observed epidemic curve of clinical cases reasonably well, and predicted that the Swiss BSE epidemic would come to an end between 2003 and 2005. The age of survivors incubating BSE is increasing. The higher than expected incidence of subclinical cases observed in animals from the culling scheme is most probably the result of the heterogeneous distribution of infected animals and affected herds in the population. The results of the model need to be taken into account when designing surveillance and testing schemes for BSE.