Risk factors for the presence of Campylobacter spp. in Dutch broiler flocks.

The campylobacter status of 495 broiler flocks sampled in The Netherlands between April 1997 and December 2000 was related to farm- and flock-specific information obtained from questionnaires to identify potential risk factors for campylobacter presence. Approximately 30% of the flocks tested positive for Campylobacter spp. in at least one pooled faecal sample. Multivariable logistic regression showed significant risk increments for: ages 29-35 days (OR = 2.34) and 36-42 days (OR = 3.96) compared to 22-28 days; > or =5 broiler houses on the premises (OR = 3.02); the presence of other farm animals on the farm (OR = 1.88); the presence of animals on farms within 1 km (OR = 9.56); and summer (OR = 3.48) and fall (OR = 2.59) compared to winter. Furthermore, hatcheries differed (ORs from 5.42 to 20.2), although this variable showed strong collinearity with the variables explaining feed mill and integrated poultry operations. We also identified interaction in which an increased risk from children entering the broiler house (OR = 28.0) was diminished by the use of broiler-specific workclothes. Population attributable fractions (PAFs) suggested that animals on farms within 1 km (PAF = 0.76) and hatchery (PAF = 0.67) had the highest impacts on campylobacter presence in Dutch broiler flocks. These factors, however, lack an easy interpretation of the mechanism behind the suggested effect.

Differences between reference laboratories of the European community in their ability to detect Salmonella species.

The ability of national reference laboratories for Salmonella of the European Union member states to detect Salmonella bacteria was tested in four collaborative studies during the period 1995 through 1999. Three different methods were prescribed in the four studies. Capsules containing various numbers of Salmonella Typhimurium or Salmonella Enteritidis were tested. In studies II, III and IV, Salmonella bacteria were isolated in the presence of competitive microorganisms. Significant differences were found between the four studies due to varying levels of difficulty with regard to the level of contamination, the use of serotypes and the presence of competitive organisms. There were also significant differences between the laboratories in the results obtained. Possible reasons for these differences will be further investigated by the European Union Community Reference Laboratory for Salmonella.

Differences between national reference laboratories of the European community in their ability to serotype Salmonella species.

The capacity of national reference laboratories of the European Union member states to correctly serotype Salmonella strains was assessed in four collaborative studies on serotyping in the period 1995-1999. Participants were asked to identify 20 strains in studies I, II and III and 16 strains in study IV, using the typing method routinely performed in their laboratory. In the first study, the strains to be identified belonged to Salmonella enterica subsp. enterica, salamae or houtenae, while in the other studies only strains belonging to Salmonella enterica subsp. enterica were included. Significant differences between laboratories and between studies were found. Differences were related to the frequency of actual occurrence of the study strains in the area served by the laboratory and the number of antisera available in the laboratory.

Comparison of selective enrichment media for the detection of Salmonella in poultry faeces.

AIMS: The aim of this study was to compare the results of semisolid media and Rappaport-Vassiliadis (RV) medium for the detection of Salmonella in faecal samples from broiler and layer flocks. METHODS AND RESULTS: Three different selective enrichment media were used: (a) RV medium; (b) diagnostic semisolid Salmonella medium (DIASALM) and (c) modified semisolid RV (MSRV) medium. The performance of DIASALM and MSRV was significantly better compared with RV. CONCLUSION: The results of this study indicate that approximately 95% of the samples containing Salmonella would be detected by a combination of a semisolid medium (MSRV or DIASALM) and RV. SIGNIFICANCE AND IMPACT OF THE STUDY: The International Standard method ISO 6579, including RV and selenite cystine broth as selective enrichment media, is most frequently used for the isolation of Salmonella from poultry faeces. This study reveals that there are more suitable combinations of selective enrichment media.

A model for evaluating intervention strategies to control salmonella in the poultry meat production chain.

A model of the transmission of salmonella through the poultry meat production chain is developed, to predict the effects of intervention strategies for salmonella control. The model first describes the situation before intervention in terms of salmonella prevalences at flock level and some transmission parameters. After single control measures are translated into effects on these transmission parameters, the effects of sets of control measures (intervention strategies), can be calculated with the model. As research data are lacking, the model input parameters were derived from expert opinion. As an example, the effects of two intervention strategies proposed for the Dutch poultry industry are predicted. A sensitivity analysis is performed to indicate where the most effective control measures may be expected. Additionally, the reliability of the model predictions is studied by an uncertainty analysis. The use of the model as a tool for policy makers deciding about salmonella control strategies is discussed.

Quantifying risk factors of coccidiosis in broilers using on-farm data based on a veterinary practice.

A study was done to find and quantify risk factors for coccidiosis. The study population consisted of 4774 broiler flocks kept on 177 farms. Flocks were considered a case when at least one bird in the flock showed microscopic presence of oocysts in intestinal scrapings in a grow-out cycle. Other flocks were defined as controls. This was done for three types of Eimeria: Eimeria acervulina, Eimeria tenella and Eimeria maxima. Logistic regression was used to assess variables that influence the occurrence of Eimeria species. There were 49 variables, based on animal, flock or farm level. There was an enhanced risk of coccidiosis due to environmental and management factors that increase the risk of introducing contamination or that are related to hygienic measures. These include lack of use of overalls by visitors, a farmyard which is difficult to clean, bad hygienic status, personnel who might also be working on other farms, presence of other animals on the farm, and feeding and drinking systems which are more difficult to clean. Also, the presence of other diseases on the farm and Eimeria species found in the previous flock increased the risk of coccidiosis.

Eimeria acervulina: influence of corticosterone-induced immunosuppression on oocyst shedding and production characteristics in broilers, and correlation with a computer simulation model.

An experiment was conducted to investigate the effects of immune responsiveness on excretion of oocysts after E. acervulina infection and subsequent effects on production characteristics of broilers (Gallus domesticus). These effects were determined in broilers repeatedly infected with 2.85 x 10(3) oocysts of E. acervulina and treated with various dosages of corticosterone in the diet (0, 10, 20 and 30 p.p.m.). Corticosterone treatment did not have an effect on the peak oocyst excretion, although it was administered from 4 days before initial infection. The number of oocysts excreted shortly after the peak and the length of the excretion period were increased in corticosterone-treated groups. The absence of a difference in peak oocyst excretion was ascribed to the existence of a time-lag between first contact with the parasite and rate of development of protective immunity. In a recently developed computer simulation model this period was assumed to be 5 days. Assuming that immunosuppression, through corticosterone, is only effective when protective immunity is in operation, the results indicate a time-lag of at least a few days, which supports the inclusion of such a time-lag in the computer simulation model. General immunosuppressive effects of the corticosterone treatment, monitored by antibodies and mitogen-induced lymphocyte stimulation confirmed that immunosuppression occurred shortly after medication started. Infection did not have a significant influence on production characteristics in animals without dietary corticosterone. However, with increasing corticosterone levels the negative effects of infection on production also increased.

Effects of initial litter contamination level with Eimeria acervulina on population dynamics and production characteristics in broilers.

The present experiment was done to obtain experimental evidence supporting the existence of an optimal initial contamination level of Eimeria acervulina with respect to broiler productivity, as suggested by simulation model outcomes. Three levels of initial (on Day 3) contamination of the litter were applied (low, intermediate and high). The peak of oocyst excretion during the flock cycle (grow-out) (Days 0-36) depended on the initial contamination level. Oocysts peaked at Day 15, 22 and 33 for the high, intermediate and low contamination level, respectively. Antibody titres and plasma carotenoid contents were not significantly affected by contamination levels. Average body weight at the end of the flock cycle (Day 36) and average daily body weight gain were significantly higher at the intermediate contamination level compared with the low and high contamination levels. Average body weight at Day 36 was 1681 g, 1712 g and 1674 g for the low, intermediate and high contamination level, respectively. Average daily weight gain was 45.7 g, 46.5 g and 45.5 g for the low, intermediate and high contamination level, respectively. Thus, the data from this experiment support the existence of an optimum initial contamination level for E. acervulina with respect to performance results.

Required thermal thresholds during transport of animals.

Conditions (total complex of stressors) during the transport of animals vary strongly between and within transports. Adverse climatic conditions are stressors that animals have to face during transport. The thermoregulation of animals id discussed with respect to threshold values for optimal climatic conditions. These thermal thresholds depend on animal related factors and environmental conditions. The specific impact of transport conditions, such as food and water deprivation, high stocking density, high humidity and high air velocity, on thermal thresholds are described.

Effects of atrophic rhinitis induced by Pasteurella multocida toxin on heat production and activity of pigs kept under different climatic conditions.

Effects of moderate, artificially induced atrophic rhinitis symptoms on level and changes in heat production and activity were determined in pigs kept under different climatic conditions. Eight groups of 30 pigs each, housed in one of two climatically controlled respiration chambers, were exposed to a 2 x 2 factorial arrangement of treatments: challenged with 0 or 13 micrograms of Pasteurella multocida toxin (Pm-T)/mL, and two climatic environments (good: 25 degrees C, or adverse: 15 degrees C with draught periods). The Pm-T challenge reduced (P < .05) day averages of total (HP) and activity-related heat production (Har). The response to Pm-T treatment was similar in both climatic environments. Differences in the heat production and activity caused by the climatic treatment declined (P < .001) with time and acclimation to the environment. Analyses of HP, Har, and activity-free heat production in 12 2-h periods showed a biphasic activity rhythm. Both treatments affected (P < .05) level of HP and Har in several of the 2-h periods, but the biphasic rhythm was not altered. Day averages of Har showed a disposition to be differently affected (P < .068) by Pm-T challenge in the climatic treatments dependent on duration of exposure. This interaction effect (P < .001) seemed to originate from the periods between 1500 and 2100. Therefore, it might be wise to distinguish between overall effects (day means) on total, activity-related, and activity-free heat production and effects within a day (e.g., 2-h means). Treatment with Pm-T seemed to suppress the general well-being of pigs, reducing pigs' activity and food intake.(ABSTRACT TRUNCATED AT 250 WORDS)

Rate and course of sporulation of oocysts of Eimeria acervulina under different environmental conditions.

An experiment was conducted to determine the rate and maximum percentage of sporulation of Eimeria acervulina oocysts at various environmental conditions relating to temperature (21 versus 33 degrees C) and relative humidity (RH) (40 versus 80%). Measurements were made during 44 h after excretion of oocysts in 3 substrates: dry litter, clammy litter and pure faeces respectively. Maximum sporulation percentage in both dry (22.6%) and clammy litter (19.5%) was higher (P < 0.005) than in pure faeces (11.6%). Neither temperature nor RH had a significant influence on percentage of oocysts that sporulated. Under these simulated practical conditions approximately 25% of all oocysts sporulated, whereas sporulation under optimal conditions (29 degrees C, aeration, 2% K2Cr2O) showed a higher (68%) sporulation ability of oocysts. At 33 degrees C sporulation proceeded at a faster pace than at 21 degrees C (P < 0.005). With respect to RH and substrate, once sporulation started, the rate of increase to maximum percentage was not different. Time of onset of sporulation was influenced by temperature (P < 0.0001) and RH (P < 0.001). Time of onset occurred 15 h later at 21 degrees C compared with 33 degrees C and 5 h later at 40% RH compared with 80%. Also, an interaction effect (P < 0.01) was found with effect of RH being stronger at 21 degrees C compared with 33 degrees C. It was concluded that the most important aspect in the epidemiology of E. acervulina during a flock cycle is the time of onset of sporulation with temperature being the most important factor.

Description of a simulation model for the population dynamics of Eimeria acervulina infection in broilers.

A simulation model for the population dynamics of Eimeria acervulina infection in broilers is presented. The model describes the development of the numbers of parasites in the various life-stages during the growing period of broilers and the empty house period between grow-outs. The model includes assumptions with respect to development of immunity to E. acervulina infection and effects of application of anticoccidial drugs. The model consists of a set of difference equations that are solved numerically at 1 h intervals. Under constant conditions, an equilibrium level was reached after a few grow-outs during which infection always peaked around the 21st day in the growing period. Within a growing period, infection peaked earlier (later) than the 21st day in case initial numbers of sporulated oocysts were higher (lower) than the equilibrium number.

Description of a model to simulate effects of Eimeria acervulina infection on broiler production.

A simulation model for effects of Eimeria acervulina infection on technical and economic characteristics in broiler production is presented. The model describes development over time of the growth depression, feed intake reduction, and decrease in feed efficiency associated with infection. The model also shows a phase of compensatory growth during which earlier negative effects are counterbalanced, at least partly. Major assumptions made were: infection with E. acervulina occurs in each flock; production is affected in each flock; compensatory growth takes place because immunity develops and cell regeneration occurs. The results show that the pattern of development of the production characteristics during a flock cycle depends on the initial contamination level. Both a high and low initial contamination level results in a lower average daily gain, a worse feed to gain ratio, and a reduced net revenue compared to an intermediate contamination level.

Circadian rhythm in heat production of limit-fed growing pigs of several breeds kept at and below thermal neutrality.

Circadian rhythm in total and activity-free heat production (H and Hacf, respectively) was studied in Norwegian Landrace (N), Finnish Landrace (F), Dutch Landrace (D), and Great Yorkshire (Y) barrows. Animals, weighing 26 kg at the start of the study, were kept in groups for 18 2-d periods in climate respiration chambers at environmental temperatures (Tenv) between 11 and 26 degrees C. Measurements of H and physical activity of the pigs were done in 12-min intervals for 36 h per breed per Tenv. Feeding level of animals in a group was 93 g.kg-.75 x d-1 (2.5 times maintenance) and based on mean BW. Circadian rhythm in H and Hacf with data excluding the feeding periods was assessed using a sine wave with a 24-h periodicity per breed and per Tenv. With respect to H, the intercepts and amplitudes for the three Landrace breeds were similar, but the Y pigs had a lower intercept and a lower amplitude. The intercepts increased with decreasing Tenv. In N pigs, but not in F, D, or Y pigs, the amplitude increased with decreasing Tenv. With respect to Hacf, all breeds had similar intercepts and amplitudes. The Hacf varied less within a day than did H. In all breeds, the intercepts were increased with decreasing Tenv. The amplitudes were not affected by Tenv.

An evaluation of immune competence in different swine breeds.

The purpose of this investigation was to establish parameters for the evaluation of immune competence in different swine breeds. Cellular and humoral immune reactivity against keyhole limpet haemocyanin (KLH) was analysed using the lymphocyte stimulation test (LST), a skin allergy test and the IgG response. Various characteristics of the KLH-specific immune response were studied in 988 sows of four breeds. KLH-specific immune responses showed considerable variability. The applied statistical model explained 63 to 73 per cent of this variation. Genetic influences, expressed as the heritability estimate, were rather high for the IgG response (0.33), as well as for the skin reaction (0.26) and the LST (0.41-0.45). A positive correlation between the various immune parameters was found. Selective breeding for immune responsiveness seems to be feasible, but selection for cellular as well as humoral immune reactivity also seems to be possible with KLH as the antigen.

Multivariate epidemiological approach to coccidiosis in broilers.

A retrospective, case-control study into risk factors of coccidiosis was undertaken using data from 189 broiler flocks. A case flock was defined as a flock in which at least one bird had intestinal lesions on 1 of 6 wk in a 42-day cycle. Flocks wherein such birds could not be detected were defined as controls. There were 187 variables, measured or derived. These were assigned to subsets of data, each subset being a group of variables representing related information. Uni- and bivariate analyses were performed in each subset. Variables and interactions that were significant in these analyses were entered into a multivariate model across subsets. In the final model, seven variables appeared to be significantly associated with detecting lesions in birds of a flock. Differences among breeds covered a range of about an 80-fold change in risk of being a case. At intermittent lighting, the risk of being a case increased about sevenfold compared with continuous lighting. A higher initial (Week 1) environmental temperature decreased the risk of finding lesions in a flock (about .8-fold per degree Celsius). This risk was also lower at a lower average aerial ammonia content (below versus above 14 ppm) and higher maximum carbon dioxide content (above versus below .4 vol%) changing the risk about .3- and .4-fold, respectively. The risk of being among cases increased with more litter (about twofold per kilogram of litter per square meter). Flocks in houses of 600 to 800 m2 were about 9.8 times more at risk of being scored as lesion-positive than those in smaller houses.(ABSTRACT TRUNCATED AT 250 WORDS)

Multivariate epidemiological approach to salmonellosis in broiler breeder flocks.

A retrospective, case-control study into risk factors of salmonellosis was undertaken using data from 111 broiler breeder flocks assembled during a 5-yr period. The results of both univariate and multivariate analyses are presented. Many different Salmonella species were detected. Multivariate models were created based on the outcome of univariate analyses. The following variables appeared to be the most relevant: disinfection tubs, hygiene barriers, the interaction of disinfection tubs by hygiene barriers, and feed mills. The final model indicated that flocks housed at farms without a disinfection tub, with poor hygiene barriers, and receiving their feed from a small feed mill had a 46.1 times greater risk of being Salmonella-positive than flocks housed at farms with a disinfection tub, with good hygiene barriers, and receiving their feed from a large feed mill. It is concluded that the application of quantitative epidemiological methods can be valuable not only to identify potential risk factors but also to quantify their contributory effect on the disease outcome. Hence, it may be a useful tool for application in "integrated food chain quality control programs".

The upper critical ambient temperature in neonatal chicks.

Heat production, dry matter, and water loss in the body and yolk sac of neonatal broiler chicks were measured during 24 h exposure to constant temperatures from 30.8 to 38.8 C. Average initial body and yolk sac weights were 41.6 and 4.4 g, respectively. Chicks housed at 30.8 C lost 3.5 g/day and chicks housed at 38.8 C lost 5.7 g/day of total body weight. Between 30.8 and 35.1 C, weight loss of the yolk sac was 1.9 g/day. At 38.8 C, weight loss of the yolk sac was 1.4 g/day. Weight lost from the yolk sac consisted of equal amount of dry matter and water. Water loss from the remainder of the chick's body (the total body without yolk sac) increased from 1.8 to 4.4 g as environmental temperature was raised from 30.8 to 38.8 C. This increase occurred mainly above about 35 C. Chick heat production increased with ambient temperature. Heat production as determined per subsequent 3-h period decreased with increasing duration of exposure from 34.6 to 28.2 kJ/kg per hour (1 kJ = .239 kcal) at 30.8 C and from 44.1 to 35.5 kJ/kg per hour at 38.8 C. The upper critical temperature was derived from regression of heat production on temperature. Results showed that this critical temperature was between 36 and 37 C.

Effects of recombinant porcine somatotropin on metabolic rate in growing pigs.

Effects of recombinant porcine somatotropin (rpST) on metabolic rate were studied in two trials with 24 crossbred barrows (Yorkshire x Landrace) in each. The barrows weighed about 80 kg (SE within trials 2.2 kg) at the start of the measurements and in each trial 12 pigs received 4 mg of rpST and 12 received a placebo. The diet contained 2.57 Mcal NE/kg and 20% CP (about 1% lysine). Animals were fed approximately 2.8 times maintenance (280 kcal ME.kg-.75.d-1). Heat production (gaseous exchange of CO2 and O2) and activity were measured continuously. Heat production associated with activity was calculated from the regression of heat production on activity. Animals treated with rpST exceeded controls in rate of gain by 252 g/d (P less than .001) and in metabolic rate by 14.5 kcal.kg-.75.d-1 (P less than .01). The rpST treatment increased rectal (+ .2 degrees C) and surface (+ .8 degrees C) temperatures. Activity-related heat production in treated pigs was increased, but this was only partly related to the increase in metabolic rate with rpST. The daily patterns of total and activity-related heat production were similar between pigs in both experimental treatments.