Economic and epidemiological evaluation of Salmonella control in Dutch dairy herds.

This paper presents an analysis of a Salmonella control program for Dutch dairy herds. Salmonella control strategies were evaluated using a computer-based model consisting of an epidemiological module and an economics module. The epidemiological module is a state transition model of the infectivity of a herd, with the unit of analysis being the individual farm. The probability of a herd going from one state in the model to another state was derived from biological characteristics of Salmonella infections in dairy herds, and the presence or absence of risk factors. The economics module was based on partial budgeting. Control measures were modeled as influencing the risk factors. Amongst the measures considered were the prohibition of transporting potentially infectious animals and manure to farms, the culling of chronically infected animals, and herd management measures such as separate housing of groups of animal that differ in age. Alternative strategies, both compulsory and obligatory, were defined and evaluated concerning the reduction of prevalence of infected herds, the cost of a strategy, and cost-effectiveness. Results of the model suggested that a compulsory control strategy which included culling chronically infected animals and prohibiting the transport of potentially infected animals reduces the prevalence of Salmonella positive herds considerably, and was most cost-effective. Adding hygienic measures and a ban on the transport of animal manure further reduces prevalence, but only slightly, and with substantially more costs.

Risk factors for clinical Salmonella enterica subsp. enterica serovar Typhimurium infection on Dutch dairy farms.

Risk factors for outbreaks in 1999 of clinical Salmonella enterica subsp. enterica serovar Typhimurium infection on dairy farms were studied in a matched case-control study with 47 case farms and 47 control farms. All 47 case farms experienced a clinical outbreak of salmonellosis which was confirmed with a positive bacteriologic culture for serovar Typhimurium in one or more samples. Serovar Typhimurium phage type 401 and 506 (definitive type 104, DT104) were the most frequently isolated phage types (13 isolates). On most farms (66%), clinical signs were seen only among adult cows. The most frequently reported clinical signs were diarrhoea (in 92% of the farms) and depression (in 79% of the farms). Control farms were matched on region and had no history of salmonellosis. A questionnaire was used to collect data on case and control farms. The relationship between serovar Typhimurium status of the farm and possible risk factors was tested using conditional logistic regression. Significant factors in the final model were presence of cats on the farm (OR=0.06), purchase of manure (OR=21.5), feeding colostrum only from own dam (OR=0.08), a non-seasonal calving pattern (OR=25), unrestricted grazing of lactating cows (OR=0.07), and a high mean mowing percentage of pasture (OR=1.02).

Herd-level diagnosis for Salmonella enterica subsp. enterica serovar Dublin infection in bovine dairy herds.

Herd-level sensitivities of bacteriological and serological methods were compared in 79 bovine dairy herds, recently infected with Salmonella enterica subsp. enterica serovar Dublin. All farms experienced clinical signs of salmonellosis for the first time and had no history of vaccination against salmonellosis. At the start of the study, infection with serovar Dublin was confirmed with at least one positive bacteriologic culture for serovar Dublin from a clinical case (gold standard for herd infection). Bacteriological culture was done on samples of dung-pits, drinking water, bulk-milk filters, and faeces of animals with current or earlier clinical signs of salmonellosis. Blood samples of all animals and bulk-milk samples were tested using an ELISA.Herd-level sensitivity (HSe) of culture of dung-pits, drinking water, bulk-milk filters, and faeces of animals with current or earlier signs of salmonellosis was 45, 5, 7, and 38%, respectively. HSe for serology of all animals was 100%. If blood samples of all calves 4-6 months old were examined, at least one calf was seropositive on 91% of the infected farms. If serology was performed on samples of animals with current or earlier signs of salmonellosis, at least one animal was seropositive on 80% of the infected farms. HSe for bulk-milk samples was 54%. However, if clinical signs of salmonellosis were observed only in lactating animals, sensitivity of bulk-milk serology was 79%. Interesting combinations of methods were the combination of serology of bulk milk with either serology of animals with current or earlier signs of salmonellosis (HSe=91%), or serology of all calves of 4-6 months old (HSe=99%).

Evaluation of two enzyme-linked immunosorbent assays for detecting Salmonella enterica subsp. enterica Serovar Dublin antibodies in bulk milk.

Two enzyme-linked immunosorbent assays (ELISAs) for the detecting Salmonella enterica subsp. enterica serovar Dublin antibodies in bulk milk were developed and evaluated for potential use in control programs. The ELISAs were based on either lipopolysacharide (LPS ELISA) or flagellar antigen (GP ELISA). Sensitivity was determined with 79 case herds with a wide range of clinical signs. Specificity was determined with 125 Dutch and 200 Swedish control herds. The relation between antibodies in bulk milk, antibodies in serum, and the level of milk production of individual cows was studied with 61 case herds. The optimal optical density (OD) values of the LPS ELISA and the GP ELISA were determined to be 0.2 and 0.5, respectively. The sensitivities of the LPS ELISA and the GP ELISA were 54 and 63%, respectively, with a specificity of 98% for both ELISAs with samples from the Dutch control herds. The specificities for samples from the Swedish herds were 100% for the LPS ELISA and 95% for the GP ELISA. The sensitivity of the combination of tests was 65% when samples were run in parallel, and the specificity was 100% when samples were run in series, irrespective of whether the samples came from Dutch or Swedish control herds. The variance (R(2)) in the OD value for bulk milk samples could be explained by the percentage of seropositive lactating cows in a herd with the LPS ELISA for 51% of the samples and with the GP ELISA for 72%. The variance in the OD value was best explained by the combination of the percentage of seropositive lactating cows in the herd and the mean log(10) serum antibody titer for that herd (R(2) = 62% for the LPS ELISA and R(2) = 75% for the GP ELISA). Case herds more often tested negative by the ELISA with bulk milk when the percentage of seropositive lactating cows was less than 5%. It is concluded that both ELISAs with bulk milk can be used in control programs to distinguish between infected and noninfected herds. Specificity can be increased by using the two tests in combination. Sensitivity was relatively low for both single tests and both tests combined.

Evaluation of three newly developed enzyme-linked immunosorbent assays and two agglutination tests for detecting Salmonella enterica subsp. enterica serovar dublin infections in dairy cattle.

In this study test characteristics of three newly developed enzyme-linked immunosorbent assays (ELISAs) for Salmonella enterica subsp. enterica serovar Dublin were evaluated and compared with two agglutination tests. The ELISAs involved were an indirect ELISA with serovar Dublin lipopolysaccharide (LPS ELISA), an indirect ELISA with serovar Dublin flagellar antigen (GP ELISA), and a double-antibody sandwich blocking ELISA that uses monoclonal antibodies against S. enterica subsp. enterica serovar Enteritidis flagellin (GM-DAS ELISA). The agglutination tests involved were two routine serum agglutination tests with either somatic (O) or flagellar (H) antigen. Diagnostic specificity of the three ELISAs was determined using 840 serum samples from seven dairy herds without any history of serovar Dublin infection. Cutoff values at a titer of 100, 100, and 10, respectively, for the LPS ELISA, GP ELISA, and GM-DAS blocking ELISA resulted in a specificity of 99.3, 100, and 100%, respectively. Using these cutoff values the LPS ELISA, GP ELISA, and GM-DAS ELISA were able to detect, respectively, 30, 46, and 38% of 50 fecal culture-positive animals from 13 herds with a recent serovar Dublin infection. With the same cutoff values, active carriers (n = 18) were detected for 94.4% with the LPS ELISA and for 100% with the GP and GM-DAS ELISAs. Kappa values determined on the results of all tests from 8 of the 13 serovar Dublin-infected herds and the 7 control herds demonstrated a good correlation between the results of all ELISAs and the H-agglutination test. The results of the O-agglutination test failed to correlate with those of the other tests. Using a set of sera from 170 aborting cows (with 25 abortions due to serovar Dublin), test results of the ELISAs and the H-agglutination test were comparable. The H-agglutination test may be used successfully for single sample testing, especially to diagnose abortion due to serovar Dublin. It is concluded that the ELISAs are useful diagnostic tools in serovar Dublin control programs and that they are preferred to agglutination tests for reasons of automation and costs.

Risk factors for Salmonella dublin infection on dairy farms.

In a case-control study of risk factors for Salmonella dublin on 126 dairy farms the following variables were significantly associated with infection. Standardized herd size and water surface area showed a positive association. Contact with cows from other herds during exchange was, unexpectedly, preventive for S. dublin infection. Purchase of cows from other herds was a risk factor. More infections occurred when the feed consisted of grass only compared to grass supplemented with maize or silage. S. dublin infection was highly associated with a liver fluke infection.

[Risk factors for Salmonella dublin infections on dairy farms]. / Risicofactoren voor Salmonella dublin-infecties op melkveebedrijven.

A case-control investigation of the risk factors for Salmonella dublin infections on 126 dairy farms identified the following variables as being significantly associated with infection: standardized farm size and presence of water courses. Contrary to expectations, contact with cattle from other farms when the animals were turned out to grass was negatively associated with S. dublin infection. The purchase of cattle from other farms was a risk factor. There were more infections when feed consisted of grass alone than when grass was supplemented with maize or grass silage. S. dublin infections were strongly correlated with liver fluke infections.

[Selenium deficiency without clinical symptoms in young cattle on a dairy farm]. / Seleendeficiëntie zonder klinische symptomen bij jongvee op een melkveebedrijf.

On a dairy farm a selenium deficiency was diagnosed on the basis of the blood chemistry of heifer calves. Of ten heifers, aged five to fourteen months, six animals had a glutathione peroxidase (GSH-PX) activity lower than 10 U/gHb. A good correlation was found between this low GSH-Px-activity and the selenium concentration in the blood. The animals had no symptoms of selenium deficiency nor elevated CPK levels. On the basis of the vitamin E-concentration in the blood it is postulated that the lack of symptom is mainly caused by the amount of vitamin E in the ration (grass and grass silage).

[An outbreak of bovine tuberculosis on a dairy farm]. / Een uitbraak van rundertuberculose op een melkveebedrijf.

An outbreak of bovine tuberculosis on a dairy farm is described. Following intradermal tuberculination 84 animals out of 111 animals older than 6 weeks had a positive reaction. Of the 34 adult sheep one gave a positive reaction. All animals on the farm were taken over for destruction by the Animal Health Centre. The source of the infection could not be established although there was a strong suspicion that the importation of three older dairy cows had introduced the infection on the farm. A further investigation was done on 45 farms. Two of these farms were infected by buying animals from the dairy farm in question. During the investigations the possible transmission of the infections to people who were in close contact to the infected animals was also investigated. From 35 examined persons 5 had a positive Mantoux-reaction. The outbreak coincided with a political discussion concerning the abolishment of the periodical tuberculination on dairy farms. Since 1 January 1993 the surveillance of bovine tuberculosis in the Netherlands is done by import control and findings in slaughter-houses combined with a good identification system. It is stressed that the examinations of the lymph glands in the slaughter-houses require the necessary attention.

[Cows with swollen anus and vulva as a husbandry problem]. / Koeien met opgezette anus en vulva als bedrijfsprobleem.

An acute farming problem is described. The symptoms were poor intake of concentrates, swelling of the anus and vulva, and decreased milk production. Research results show that pig premix was incorporated into the concentrate for dairy cows. Which component of the concentrate was responsible for the symptoms remains to be established.

Haemorrhagic claw lesions in newborn piglets due to selenium toxicosis during pregnancy.

In a sow herd piglets were born with haemorrhagic lesions on the proximal wall and sole of the claws of all their feet due to abnormal horn formation. High concentrations of selenium were detected in the liver and kidney of the piglets and appeared to be associated with these lesions. A selenium rich premix added to the rations of the sows in the second half of gestation was the origin of this selenium intoxication.

Growth of rearing calves in relation to lysine contents of milk replacer and calf starter and feeding frequency of milk replacer.

In two factorial feeding experiments with 90 and 102 rearing calves the effect of addition of extra lysine to the milk replacer in combination with a low and high lysine content of the calf starter on dry matter intake and weight gain was studied. Once or twice daily milk feeding was also compared. The calves received milk replacer up to the age of 8 weeks and calf starter and hay ad libitum from the 3rd week on. The experiments lasted to the age of 12 respectively 10 weeks. In the first experiment increasing the lysine content of the milk replacer from 14.5 g/kg to 18.5 g/kg had no effect on dry matter intake and weight gain. In the second experiment increasing the content of lysine to 17 g/kg resulted in higher intake of dry matter and higher weight gain, but only in combination with a calf starter with a low lysine content (6 g/kg). In the first experiment twice daily milk feeding resulted in higher intake of concentrate and higher weight gain as compared to once daily. In the second experiment this was only so if the starter had the lower lysine content. Increasing the lysine content of calf starter from 7 to 8.5 g/kg had no effect on dry matter intake and weight gain in the preweaning period in the first experiment. In the second experiment increasing the lysine content from 6 to 8.5 g/kg led to higher intake of concentrate and higher weight gain. This effect was only seen if the milk replacer had no extra lysine added. In the postweaning period there was no effect of increasing the lysine content from 7 to 8.5 g/kg (Exp. I). Increasing the lysine content from 6 to 8.5 g/kg led to higher dry matter intake and higher weight gain (Exp. II). These results are discussed in the light of the partial degradability of the concentrate protein in the rumen and the effect of duodenally available lysine on feed intake and weight gain.