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Søren Saxmose Nielsen

Publications and source records attributed to Søren Saxmose Nielsen.

5 recordsLinked to original sources
PubMed2006

A stochastic model simulating paratuberculosis in a dairy herd.

Paratuberculosis (PTB) causes severe economic losses to farmers and the infection has very complex effects (many indirect) on the production of a dairy herd. These indirect effects have not or only briefly been described by earlier PTB-simulation models, and therefore they were included in a new model called PTB-Simherd. Our aim was to develop the basis for a decision-support tool which can predict herd-specific production-related effects from introduction of different control strategies against PTB. The PTB-Simherd is a dynamic, stochastic, and mechanistic Monte-Carlo model simulating a dairy herd including young stock. Paratuberculosis and relevant control strategies against this infection were built into an existing herd simulation model. The model simulates epidemiological and production related consequences of PTB and control strategies against it in the herd. It also reflects indirect effects of PTB and control strategies through effects on replacements and herd demographics. Every animal in the herd is specified with biological parameters (including PTB state and test results) and it is updated in weekly time-steps. Management is specified at herd level with 353 parameters of which 78 are related to PTB. To demonstrate the basic characteristics of the model, scenarios with varying infection risks (sensitivity analyses) plus scenarios with seven different control strategies in two herds with good and poor reproduction were simulated for 10 years. Breaking of infection routes turned out to be the only strategy predicted to reduce the true prevalence of PTB in a herd. Supplementing this strategy with test-&-cull strategies had limited effect on prevalence and using test-&-cull alone just delayed the increase in prevalence. The effects of different PTB-control strategies on the production (especially sale/purchase of heifers, feed consumption and prevalences of other diseases) were predicted to be affected by other conditions like heat-detection success, replacement% and herd demographics--which were again affected by PTB infection of the herd. These links and indirect effects of control strategies thus seem important to include when modeling and predicting effects of PTB control in dairy herds.

Animals↗
PubMed2006

Simulated economic effects of improving the sensitivity of a diagnostic test in paratuberculosis control.

Low sensitivity (Se) of diagnostic tools is often mentioned as a major problem in the control of paratuberculosis (PTB) and much effort is put into the improvement of these tests. The hypothetical perspectives of improving the Se of a milk-antibody ELISA (hereafter: milk-ELISA) used in test-&-cull strategies against PTB in dairy cattle were investigated by simulations. The current Se varies between 10 and 80%, increasing with increasing lactation stage, parity and infection stage. We simulated the effects on a dairy herd's production of improving this Se to 80% (independent of these factors) and assumed no concomitant decrease in specificity. By using a PTB model called PTB-Simherd, 12 scenarios were simulated to study three test-&-cull strategies in each of four herds with 200 dairy cows. To show the maximal effect of using test-&-cull with such an improved test we simulated three strategies: (1) no testing, (2) testing with milk-ELISA test with the current Se and culling of positive cows immediately and (3) testing with milk-ELISA test with a Se improved to 80% and culling positive cows immediately. The four herds were defined by a moderate (25%) or high (80%) initial true within-herd prevalence (including young stock), and a poor or good heat-detection success of 40 or 60%. We assumed that these factors influenced the effects of improving the Se of the milk-ELISA. Management both concerning calf management and in general was specified to represent a typical Danish herd. Using an improved milk-ELISA was predicted to reduce the prevalence of PTB more effectively than the current ELISA, and over 10 years bring the production of a herd with moderate initial prevalence up to a production level comparable to a non-infected herd (unlike if the current ELISA had been used). In a herd with high initial prevalence (80%) milk production was increased more by using the improved milk-ELISA, but after 10 years the replacement rate was still very high causing problems with having enough recruitment animals-especially in high-prevalence herds with poor reproductive performance. Economically important measurements in all four herds benefited from the improvement of the test over a 10-year period. However, in the first 3-5 years the improved test would be more expensive to use than the current test, due to increased replacement (reduced net annual revenue per cow euro15 on average) but after that, net annual revenue increased continuously; after 10 years it was euro70-90 higher, than if the current milk-ELISA was used. Also, the milk-ELISA test with its current Se seemed to be profitable already after 2 years in high-prevalence herds using a test-&-cull strategy based on the milk-ELISA alone.

Animals↗
PubMed2004

Pestivirus exposure in free-living and captive deer in Austria.

During the hunting season of 2001-02, blood and spleen samples from 59 red deer (Cervus elaphus), 77 roe deer (Capreolus capreolus), four fallow deer (Dama dama), and five chamois (Rupicapra rupicapra) were collected from nine hunting districts (n = 133) and one deer farm (n = 12) in southern Austria. Sera were tested for antibodies against bovine viral diarrhea virus (BVDV) with an enzyme-linked immunosorbent assay (ELISA) and virus neutralization tests against three BVDVs and one border disease virus strain. Reverse transcriptase polymerase chain reaction was used for detection of pestivirus-specific RNA in spleen samples. Antibodies were detected in one serum sample when using ELISA and virus neutralization tests. Results of the virus neutralization tests of this sample provided strong evidence for the exposure to the BVDV-1 genotype. The spleen samples were negative for pestivirus-specific RNA.

Animals↗
PubMed2003

Prevalence and transmission of haemolytic Gallibacterium species in chicken production systems with different biosecurity levels.

A stratified cross-sectional study consisting of four strata of biosecurity based on production system type, including organic/free-range layer, battery-cage layer, layer parent, broiler parent and broiler grandparent flocks, was performed to estimate the prevalence of haemolytic Gallibacterium spp. Thirty birds were sampled by tracheal and cloacal swabs in each flock. A flock was considered infected when just one bird tested positive. A total of 27 flocks was included in the study. All chickens from the broiler grandparent flocks sampled negative, whereas 28% of the broiler parents, 40% of the layer parents, 67% of the battery-cage layers and 96% of the organic/free-range chickens sampled positive. A total of 95.9% (standard deviation +/- 7.6%) of birds from infected flocks was colonized by haemolytic Gallibacterium species. A significantly higher number of tracheal swabs was positive compared with cloacal swabs. The probability of vertical transfer was investigated by sampling offspring from an infected as well as a non-infected parent flock. None of the samples were found positive. In conclusion, we showed that haemolytic Gallibacterium spp. were widely distributed within the Danish commercial chicken production systems. However, prevalence proportions were highly influenced by the production system and found to be significantly associated with the biosecurity level observed in the flocks. In general, flock infections resembled an 'all or none' type of colonization as practically all of the chickens in infected flocks sampled positive. There was no evidence of vertical transmission of Gallibacterium.

Animal Husbandry↗