Biomedical subjects

M Nielen

Publications and source records attributed to M Nielen.

At least 37 records · Page 2Linked to original sources

PubMed2000

[Heck cattle in the Oostvaardersplassen: risk for infectious diseases or not?].

This article discusses risk analysis of infectious diseases in a cattle population. Heck cattle living in nature reserve 'De Oostvaardersplassen' were studied as an example of the risk analysis approach. Twenty-five adult cattle were tested for every infectious disease agent that the risk analysis indicated might be prevalent. All sampled cattle tested positive for Bovine Herpesvirus 1, whereas the prevalence of antibodies against other infectious disease agents was below the level that was assumed to be the threshold for spread of the disease to cattle in the surrounding areas. Risk management of infectious diseases was expressed in a so-called 'low-risk profile'. The risk of introduction or spread of infectious diseases was estimated to be very low as long as the population was kept strictly enclosed.

Animals↗

PubMed2000

Relationship among estradiol, cortisol and intensity of estrous behavior in dairy cattle.

Economic profitability of a dairy farm is based, in part, on the calving interval of the cows. The optimal interval is 365 d. To achieve this, the cow needs to be pregnant within 85 d post partum. The first and most problematic step in this process is the determination of the optimal time for insemination, which is based on estrous behavior. The expression of estrous behavior, however, is at a low level in modem dairy herds, resulting in low detection rates and longer calving intervals. In the present study, a point scale was used to monitor postpartum, nonpregnant cows for estrous symptoms. Frequent blood samples were taken around estrus, and the cows were fit with pedometers to measure their activity. Correlations between the occurrence of symptoms of estrus and levels of estradiol and cortisol were then analyzed. Standing heat, the standard symptom of estrus, was observed in only 53% of the cows. A high correlation of 0.7 was found between estradiol concentration and estrous behavior. This was empasized by the fact that the estradiol level reached its highest level of 7.76 + 2.39 (SD) pg/mL at the same time as the highest behavior score. The highest pedometer readout lagged 8 h behind this moment. Cortisol levels did not exceed the physiological levels in rest situations but showed an increase at the time estrous behavior was at its maximum. The present study showed that standing heat is not the primary symptom for detecting estrus in cows. Pedometers are a useful aid but they have to be read several times a day. The high correlation between the visual symptoms of estrus and estradiol concentrations indicates that visual estrus detection is an efficient, reliable way to determine the right time for insemination.

Animals↗

PubMed2000

Low somatic cell count: a risk factor for subsequent clinical mastitis in a dairy herd.

A case-control study was conducted to evaluate factors measured at the udder inflammation-free state as risk factors for subsequent clinical mastitis. The factors including somatic cell count (SCC), body condition score, milk yield, percentages of milk fat and milk protein, and diseases were evaluated for their association with the results of udder inflammatory response. The results of the response were specified as presence (case) and absence (control) of clinical signs of mastitis. Data on Holstein Friesian cows calving from January 1984 to November 1996 from a commercial farm with low bulk milk SCC were used. Univariable and multivariable random-effect logistic models were used to evaluate the effect of those factors on the risk of clinical mastitis. The following variables were associated with increased odds of case versus control events in the univariable analysis: early lactation period, low SCC, high milk yield, high percentage of milk protein, high percentage of milk fat, low body condition score, retained placenta, and milk fever. For the final multivariable model of all variables used for analysis, only low SCC remained significantly associated with increased risk of subsequent clinical mastitis. The authors concluded that very low SCC during the udder inflammation-free state are associated with increased risk of clinical mastitis.

Animals↗

PubMed1999

Spatial and stochastic simulation to evaluate the impact of events and control measures on the 1997-1998 classical swine fever epidemic in The Netherlands. I. Description of simulation model.

The simulation model InterCSF was developed to simulate the Dutch Classical Swine Fever (CSF) epidemic of 1997-98 as closely as possible. InterCSF is a spatial, temporal and stochastic simulation model. The outcomes of the various replications give an estimate of the variation in size and duration of possible CSF-epidemics. InterCSF simulates disease spread from an infected farm to other farms through three contact types (animals, vehicles, persons) and through local spread up to a specified distance. The main disease-control mechanisms that influence the disease spread in InterCSF are diagnosis of the infected farms, depopulation of infected farms, movement-control areas, tracing, and pre-emptive slaughter. InterCSF was developed using InterSpread as the basis. InterSpread was developed for foot-and-mouth disease (FMD). This paper describes the process of modifying InterSpread into InterCSF. This involved changing the assumptions and mechanisms for disease spread from FMD to CSF. In addition, CSF-specific control measures based on the standard European Union (EU) regulations were included, as well as additional control measures that were applied during the Dutch epidemic. To adapt InterCSF as closely as possible to the Dutch 1997/98 epidemic, data from the real epidemic were analysed. Both disease spread and disease-control parameters were thus specifically based on the real epidemic. In general, InterSpread turned out to be a flexible tool that could be adapted to simulate another disease with relative ease. The most difficult were the modifications necessary to mimic the real epidemic as closely as possible. The model was well able to simulate an epidemic with a similar pattern over time for number of detected farms as the real outbreak; but the absolute numbers were (despite many relevant modifications) not exactly the same--but were within an acceptable range. Furthermore, the development of InterCSF provided the researchers with a better insight into the existing knowledge gaps. In part II (see the final paper in this issue), InterCSF was used to compare various control strategies as applied to this epidemic.

Animal Husbandry↗

PubMed1999

Spatial and stochastic simulation to evaluate the impact of events and control measures on the 1997-1998 classical swine fever epidemic in The Netherlands. II. Comparison of control strategies.

Using the spatial, temporal and stochastic simulation model InterCSF, several alternative pre-emptive slaughter strategies that could have been applied in the Dutch Classical Swine Fever (CSF) epidemic of 1997-1998 were evaluated. Furthermore, effects of changes in some disease-spread and disease-control parameters were studied. InterCSF simulates the spread of CSF between farms through local spread and contacts (animals, transport and persons). Disease spread is affected by control measures implemented through different mechanisms (e.g. depopulation of infected farms, pre-emptive slaughter, movement control). The starting point for the evaluation of strategies was a simulated basic scenario, which mimicked the real epidemic. Strategies were compared using epidemiological as well as economic results. Economic results were generated by a separate model (EpiLoss) that calculated the direct losses and consequential losses for farmers and related industries. The comparison of the different alternatives to the basic scenario led to some general conclusions on the Dutch CSF-epidemic. Pre-emptive slaughter seemed to be an effective strategy to reduce the size of an epidemic, if started at an early stage. Economically, pre-emptive slaughter was not as expensive as expected; the resulting smaller size of the epidemic, combined with less welfare slaughter, led to much lower overall losses. Furthermore, although large movement control areas seemed effective in reducing the size of the epidemic, the total losses were relatively high because of subsequent welfare slaughter. If infection probabilities could be reduced, for example by improved biosecurity, the resulting epidemics would be much smaller.

Animal Husbandry↗

PubMed1999

Relationships between dairy cow mastitis and fertility management and farm performance.

A field study was carried out on 38 dairy farms in the Netherlands to determine the relationship between mastitis and fertility management with 305-day milk production and gross margin. Questionnaires were used to get insight into the farmers' management. Out of 150 variables related to mastitis and fertility management, and technical and economic results, 44 variables were selected based on correlation of > or = 0.25 or < or = -0.25 with milk production and/or gross margin. These variables were used in two separate partial least squares (PLS) analyses. PLS has the advantage that it can handle a large number of variables in relation to the number of cases. The PLS-model of 305-day milk production had R2 = 0.54 and showed a positive relation between 305-day milk production and awareness of the farmer regarding bulk somatic-cell count (BSCC), the goal level of the farmer for BSCC, and hygiene of the milking parlour. Fertility was negatively related to 305-day milk production, in spite of a relatively good fertility management on high-producing farms. R2 = 0.46 for gross margin. The aspiration level of fertility did not seem to affect gross margin, but awareness of BSCC and calving interval (CI) had positive effects. Such awareness seemed a general parameter for good economic results, because it was correlated with different aspects of gross margin.

Animal Husbandry↗

PubMed1999

Beta-hydroxybutyrate levels in peripheral blood and ketone bodies supplemented in culture media affect the in vitro chemotaxis of bovine leukocytes.

The role of ketone bodies on chemotactic capacities of leukocytes was characterized in two experiments. Experiment I was performed to investigate the association between serum beta-hydroxybutyrate concentrations (BHB) and in vitro chemotaxis of leukocytes. Cows were divided into low-BHB, medium-BHB, and high-BHB ones and classified according to their BHB. Leukocytes from high-BHB cows had a significantly lower chemotactic differential than leukocytes from low-BHB cows (p < 0.01). The effect of adding ketone bodies into in vitro chemotaxis cultures on leukocytes chemotaxis was studied in Experiment II. Either individual or a combination of commercial ketone bodies - sodium salts of BHB (BHBA), lithium salt of acetoacetate (ACAC), and acetone (Acetone) - were diluted in culture media and divided into eight concentrations corresponding to concentrations of bovine subclinical and clinical ketosis. For leukocytes from medium- and high-BHB cow, the chemotactic indexes of leukocytes were reduced by ACAC and Acetone. Chemotactic differentials of cultures with ACAC and acetone supplementation from both sources of leukocytes were significantly lower than that of the control culture (p < 0.05). For leukocytes from high-BHB cows, chemotactic indexes were suppressed in a ketone-body environment. In conclusion, leukocytes from naturally-occurring ketotic cows have lower chemotactic differentials than those from non-ketotic cows, and a chemotactic capacity indicated by a chemotactic differential is impaired when leukocytes migrate in an environment with ketone bodies in vitro.

3-Hydroxybutyric Acid↗

PubMed1999

The effectiveness of routine serological surveillance: case study of the 1997 epidemic of classical swine fever in The Netherlands.

The authors describe the value of routine serological surveillance in detecting the introduction of classical swine fever virus into a disease-free population. The first investigation concerned the question of whether the epidemic of classical swine fever (CSF), which occurred from 1997 to 1998 in the Netherlands, could have been detected using the existing monitoring system for notifiable diseases. The investigation used data from the CSF epidemic of 1997/1998 and from the existing monitoring system. Secondly, the probability of detecting a case of CSF using routine serological surveillance was modelled both for multiplier herds and for finishing herds, and then for different herd size categories. The first investigation concluded that the probability of detecting the epidemic at the current level of routine serological surveillance is very low. The second investigation concluded that even employing a sampling scheme of sixty blood samples per month, the probability of detecting an outbreak of CSF within forty days of the introduction of the virus, is less than 40%.

Animals↗

PubMed1999

Modeling the effect of an outbreak of bovine herpesvirus type 1 on herd-level milk production of Dutch dairy farms.

One of the impacts of disease is its effect on milk production. In the present study the effect of an outbreak of bovine herpesvirus type 1 on milk production at the herd level of certified bovine herpesvirus type 1-free dairy farms was modeled. The objective was to study several linear models to quantify the effects of a bovine herpesvirus type 1 outbreak on milk production accounting for the repeated measurements and incorporating our assumptions about the most likely duration of effects of this virus. Because milk production is measured at regular intervals, the data consisted of repeated measurements at the herd and cow levels. A marginal model, a subject-specific random-effect model, and a transition model were developed. The effect of a bovine herpesvirus type 1 outbreak was statistically significant in the random-effect model, and this model fitted the investigated farms best. However, a transition model might be a better model for generalizing the results to the whole population of Dutch dairy farms. The effect of a bovine herpesvirus type 1 outbreak on milk production derived from the random-effect model amounted to, on average, a loss of 0.92 kg of milk per cow per day during a period of 9 wk. The milk production loss varied from almost none to 2 kg of milk per cow per day. This reduction resulted in an average loss of Dfl 372 (Dfl1 = $US $0.50) with lower and upper confidence limits of, respectively, Dfl 12 and Dfl 730 per bovine herpesvirus type 1 outbreak.

Animals↗

PubMed1998

A Cox proportional-hazards model with time-dependent covariates to evaluate the relationship between body-condition score and the risks of first insemination and pregnancy in a high-producing dairy herd.

The objective of this study was to determine the relationship between body-condition score and postpartum reproductive efficiency in dairy cattle. Data on body-condition score, reproduction, diseases, and production from 1404 lactations of 639 cows, calving between January 1984 and November 1996 on a commercial farm, were used. The Cox proportional-hazards model with time-dependent covariates was used to qualify the relationship between body-condition score on a scale of 1 to 5 and risks of first insemination and pregnancy. Cows with body condition at calving < 3 had lower first-insemination risks. Loss of body-condition score between calving and 45 days after calving was associated with increased days open and days-to-first insemination. Cows with body-condition scores < 2 after Day 45 and before first insemination were less likely to be inseminated and become pregnant compared with cows that had higher body condition. Milk yield, mastitis, lameness, milk fever and genital infection were associated with a reduction in reproductive efficiency. The results indicated that loss of body-condition and actual body-condition scores before conception or first insemination or both can be used as a prognosis for days open and days-to-first insemination in dairy herds.

Animals↗

PubMed1998

Risk factors for existence of Bovine Herpes Virus 1 antibodies on nonvaccinating Dutch dairy farms.

A more closed farming system may prevent introduction of infectious diseases on dairy farms and can be a good starting point for control of these diseases. Data were available on the presence of Bovine Herpes Virus 1 (BHV1) antibodies in bulk milk and/or blood samples of Dutch dairy farms. Furthermore, information about the possible risk factors for introduction of infectious diseases was collected on 214 of these dairy farms. Data of 107 farms which had been never vaccinated against BHV1 remained for the analysis. A positive BHV1 status on these 107 farms could only be caused by introduction of BHV1. Risk factors for introduction of BHV1 on the farms were quantified using logistic regression. BHV1-positive farms purchased cattle and participated in cattle shows more often compared with BHV1-negative farms. A BHV1-positive farm also had more (professional) visitors in the barn who used farm clothing less often. The BHV1-positive farms were found to be situated closer to other cattle farms compared with the BHV1-negative farms.

Analysis of Variance↗

PubMed1996

[I&R (identification and registration) system cattle: an analysis of its use during a foot-and-mouth-disease outbreak in The Netherlands].

The performance of the Dutch cattle I&R system was analysed, with emphasis on the potential use of the system for the control of an outbreak of foot and mouth disease (FMD). The analysis showed that not all mutations were centrally registered within the three working days that are allowed to pass between the actual change and the obligatory report. In particular, young calves and cattle heading for slaughter were reported too late. During an outbreak of FMD, the best strategy to trace animals off a farm seems to be first to identify all animals on the farm, using a preprocessed list of the animals that should be present on the farm according to the I&R system. Then all the animals that have left the farm during the last month can be traced in the central I&R computer or by asking the person to whom the farmer sold the cattle (the next owner). In the present study, 54% of the animals were localized within one day, and 94% within one week. Finally, some suggestions for improvement for the system are given.

Animal Husbandry↗

PubMed1995

[Testing area Wehl: study of risks of contacts in behalf of foot-and-mouth disease].

A study on contacts between livestock holdings was conducted in a geographically defined area of 4 by 6 km in the Netherlands. The farmers were asked to record all contact on and off farm during a period of 2 weeks. The number of contacts in the 2 week period was high, on average 91.8 contacts per farm. The risk of spreading foot-and-mouth disease on or off the farm was greater for cattle farms than for swine farms. Relatively more people had contact with the animals while visiting cattle farms, thereby causing the higher risk. Most contacts occurred over short distances. Almost 50% of the contacts were within the research area. This finding confirms the importance of restricted areas around farms with foot-and-mouth disease infections.

Animal Husbandry↗

PubMed1995

[Subclinical and clinical mastitis on dairy farms in The Netherlands: epidemiological developments].

In this review a number of the main epidemiological developments in the field of udder health in the Netherlands are summarized. The changes considering the bulk milk somatic cell count are described, as are the population dynamics of subclinical mastitis. Additionally, clinical mastitis caused by Escherichia coli and Staphylococcus aureus and their risk factors are reviewed. Finally, some future developments and the possible applications of these developments are discussed.

Animals↗

PubMed1995

Bovine respiratory syncytial virus reinfections and decreased milk yield in dairy cattle.

The influence of Bovine Respiratory Syncytial Virus (BRSV) reinfections on the daily milk yield was studied by evaluating the milk production of 32 BRSV reinfected cows. For the estimation of milk production losses, four lactation curve models were used, including a gamma function, a second degree polynomial, and both of these models with a lag variable. Bovine respiratory syncytial virus reinfections seemed to have only a small effect on the daily milk production. Comparison of the true production with an estimated production according to the gamma function showed that the production for first lactation cows dropped 0.14 kg on average and for cows in their second or later lactation 0.56 kg on average, during 5 consecutive days in the infection period. For the second-degree polynomial model these values were respectively 0.42 kg and 0.80 kg. All calculated average production losses were relatively small and not significant (P > 0.15). The models without lag variable were more suitable than the models with the lag variable to estimate small production losses caused by BRSV reinfections. The power of this study was sufficient to detect a decrease in production of approximately 1-1.5 kg milk per cow per day. It was therefore concluded that BRSV reinfections were not associated with an important loss of milk production.

Animals↗

PubMed1995

Detection of subclinical mastitis from on-line milking parlor data.

A model, based on automatically collected data, was developed for detection of subclinical mastitis. The logistic regression model was based on the following variables: milk electrical conductivity, milk production, parity, and DIM. Subclinical mastitis was defined as a minimal period of 1 wk in which the SCC was > 500 x 10(3) cells/ml. In contrast, periods were defined as healthy if the SCC was < 200 x 10(3) cells/ml. The resulting model had a sensitivity of 55% and specificity of 90% for individual milkings. For periods of 14 milkings, sensitivity was 54% and specificity 92% when the threshold for that period was > 6 electrical conductivity signals for high SCC. Based on these test characteristics, the model could be used as an initial screening tool in a herd with a high incidence of subclinical mastitis. Cows with a signal would have a higher probability of being diseased than the total population. In such herds, separation of milk from the signaled cows might be a possible management strategy to reduce the SCC in the bulk milk tank.

Animals↗

PubMed1995

Comparison of analysis techniques for on-line detection of clinical mastitis.

Three techniques were compared for analysis of automatically collected data from the milking parlor. Mammary quarters showing signs of clinical mastitis were compared with randomly selected healthy quarters. Automatic data were analyzed from the milking on which the milkers observed clinical mastitis as well as data from the two prior milkings. Electrical conductivity of milk was not corrected for individual cows. Milking parlor data were preprocessed so that information on the electrical conductivity pattern during a milking was retained. Principal component analysis was used to verify whether variation in the data was caused by mastitis. Performance of logistic regression models for detection of clinical mastitis was compared with that of backpropagation neural networks. Variation in the quarter data was caused by mastitis. Automatic data from infected quarters did not always differ from data from healthy quarters, especially from the two prior milkings. The detection performance of the logistic regression model was similar to that of the neural networks. When both models were tested on the development data, sensitivity was approximately 75%, and specificity was approximately 90% at the milking of mastitis observation. Detection results were lower for the prior milkings. Therefore, not all incidences of clinical mastitis cases could be detected before clinical signs occurred.

Animals↗

PubMed1994

Evaluation of a prototype on-line electrical conductivity system for detection of subclinical mastitis.

A prototype on-line system for measurement of electrical conductivity of quarter milk was evaluated for accuracy in detection of subclinical mastitis compared with that of bacteriological culture and SCC of sampled quarters. Because of the low quarter prevalence of mastitis, quarters were sampled conditionally from the signals of the on-line system. All signaled quarters and a random selection of the nonsignaled quarters were sampled. To calculate sensitivity and specificity, the total number of non-signaled quarters was extrapolated. The system identified correctly 18 out of 23 subclinical quarters and 521 out of 555 healthy quarters. Quarter prevalence was about 1%. Predictive value of a positive test (35%) and the predictive value of a negative test (99%) were calculated, as well as sensitivity (25%) and specificity (99%), after extrapolation of the total number of nonsignaled quarters. Because of repeated measurements, sensitivity may be underestimated. When signaled quarters were defined by repeated signals within 14 d, predictive value positive increased to 48%. The prototype on-line system did not detect subclinical mastitis very accurately because of suboptimal test characteristics.

Animals↗