An attempt to define the sodium requirements of lactating dairy cows in a tropical environment

BACKGROUND: Lactating dairy cattle in the tropics may require more sodium (Na) owing to the hot and humid climatic conditions. It is unknown whether the current recommendations on Na for lactating cows can be quantitatively used in tropical countries. This study attempted to define the Na requirement of lactating dairy cows under tropical conditions by measuring Na levels in saliva, milk and faeces. RESULTS: The concentrations of Na and potassium (K) in milk, faeces and serum were not affected by dietary treatments. The amount of Na absorbed by cows fed the basal (low-Na) diet containing 0.4 g Na kg-1 dry matter (DM) was equal to the amount of Na lost in the milk, showing that these animals were fed an Na-deficient ration. This observation was corroborated by salivary Na and K levels, with the cows on the low-Na diet having salivary Na concentrations below 120 mmol L-1 in combination with salivary K concentrations above 20 mmol L-1 (P <0.05). CONCLUSION: Consumption of a daily ration formulated to contain the current Na requirement set by the NRC appears to provide too much Na for lactating cows under tropical conditions. A tentative value of 1.2 g kg-1 DM is proposed as the Na requirement for dairy cows under tropical conditions. Copyright © 2011 Society of Chemical Industr

A description and qualitative comparison of the elements of heterogeneous bovine viral diarrhea control programs that influence confidence of freedom

For endemic infections in cattle that are not regulated at the European Union level, such as bovine viral diarrhea virus (BVDV), European Member States have implemented control or eradication programs (CEP) tailored to their specific situations. Different methods are used to assign infection-free status in CEP; therefore, the confidence of freedom associated with the “free” status generated by different CEP are difficult to compare, creating problems for the safe trade of cattle between territories. Safe trade would be facilitated with an output-based framework that enables a transparent and standardized comparison of confidence of freedom for CEP across herds, regions, or countries. The current paper represents the first step toward development of such a framework by seeking to describe and qualitatively compare elements of CEP that contribute to confidence of freedom. For this work, BVDV was used as a case study. We qualitatively compared heterogeneous BVDV CEP in 6 European countries: Germany, France, Ireland, the Netherlands, Sweden, and Scotland. Information about BVDV CEP that were in place in 2017 and factors influencing the risk of introduction and transmission of BVDV (the context) were collected using an existing tool, with modifications to collect information about aspects of control and context. For the 6 participating countries, we ranked all individual elements of the CEP and their contexts that could influence the probability that cattle from a herd categorized as BVDV-free are truly free from infection. Many differences in the context and design of BVDV CEP were found. As examples, CEP were either mandatory or voluntary, resulting in variation in risks from neighboring herds, and risk factors such as cattle density and the number of imported cattle varied greatly between territories. Differences were also found in both testing protocols and definitions of freedom from disease. The observed heterogeneity in both the context and CEP design will create difficulties when comparing different CEP in terms of confidence of freedom from infection. These results highlight the need for a standardized practical methodology to objectively and quantitatively determine confidence of freedom resulting from different CEP around the world

Output-based assessment of herd-level freedom from infection in endemic situations:Application of a Bayesian Hidden Markov model

International audienceCountries have implemented control programmes (CPs) for cattle diseases such as bovine viral diarrhoea virus (BVDV) that are tailored to each country-specific situation. Practical methods are needed to assess the output of these CPs in terms of the confidence of freedom from infection that is achieved. As part of the STOC free project, a Bayesian Hidden Markov model was developed, called STOC free model, to estimate the probability of infection at herd-level. In the current study, the STOC free model was applied to BVDV field data in four study regions, from CPs based on ear notch samples. The aim of this study was to estimate the probability of herd-level freedom from BVDV in regions that are not (yet) free. We additionally evaluated the sensitivity of the parameter estimates and predicted probabilities of freedom to the prior distributions for the different model parameters. First, default priors were used in the model to enable comparison of model outputs between study regions. Thereafter, country-specific priors based on expert opinion or historical data were used in the model, to study the influence of the priors on the results and to obtain country-specific estimates.The STOC free model calculates a posterior value for the model parameters (e.g. herd-level test sensitivity and specificity, probability of introduction of infection) and a predicted probability of infection. The probability of freedom from infection was computed as one minus the probability of infection. For dairy herds that were considered free from infection within their own CP, the predicted probabilities of freedom were very high for all study regions ranging from 0.98 to 1.00, regardless of the use of default or country-specific priors. The priors did have more influence on two of the model parameters, herd-level sensitivity and the probability of remaining infected, due to the low prevalence and incidence of BVDV in the study regions. The advantage of STOC free model compared to scenario tree modelling, the reference method, is that actual data from the CP can be used and estimates are easily updated when new data becomes availabl

Transmission of highly pathogenic avian influenza H7 virus

Knowledge of the transmission of highly pathogenic avian influenza (HPAI) virus still has gaps, complicating epidemic control. A model was developed to back-calculate the day HPAI virus was introduced into a flock, based on within-flock mortality data of the Dutch HPAI H7N7 epidemic (2003). The method was based on a stochastic epidemic model in which birds move from being susceptible, latently infected and infectious, to death. Our results indicated that two weeks can elapse before a noticeable increase in mortality is observed after a single introduction into a flock. Furthermore, field data were used to estimate the transmission rate parameter beta and the influence of risk factors on within-flock transmission. Daily mortality data again were back-calculated to fit a susceptible – infectious – dead format. The method took into account the uncertainty of the length of the latent period, the survival of an infection by some birds and the influence of farm characteristics. The beta was estimated at 4.50 per chicken per day (95% CI: 2.68 – 7.57) with a bird-infectious period of four days. In contrast to general belief, none of the studied risk factors (housing system, flock size, species, age of the birds and date of depopulation) had significant influence on the estimated beta. The same method was used on field data of the HPAI H7N1 epidemic in Italy in 1999-2000. The bird-infectious period was assumed to be two days, and all birds were assumed to die after this infectious period. The estimated beta for HPAI H7N1 virus transmission in turkeys was 1.43 (95% CI: 1.17 – 1.74). Farm risk factors such as flock size and age of the turkeys again did not influence beta. The effect of vaccination on HPAI H7N7 transmission in turkeys was estimated by means of a transmission experiment. Cloacal and tracheal swabs (for real-time RT-PCR) and serum samples (for hemagglutination inhibition test) were taken to monitor the infection both in inoculated and in susceptible contact turkeys, which were all either unvaccinated, vaccinated once or vaccinated twice with H7N1. Unvaccinated contact birds had a mean infectious period of 6.2 days, and an estimated beta of 1.26 per infectious bird per day. However, no virus shedding was found in inoculated vaccinated turkeys and thus we concluded that vaccination with H7N1 protected against challenge with HPAI H7N7 virus. During the Dutch epidemic a large number of human infections were reported. We estimated infection probabilities for persons involved in disease control on infected farms. Case definition was based on self-reported conjunctivitis and positive hemagglutination inhibition test. A high infection probability during a farm-visit was associated with clinical inspection of poultry in the area surrounding infected flocks (7.6%, 95% CI: 1.4 – 18.9%) and active culling during depopulation (6.2%, 95% CI: 3.7 – 9.6%). Low probabilities were estimated for managing biosecurity (0.0%, 95% CI: 0.0 – 1.0%) and cleaning assistance during depopulation (0.0%, 95% CI: 0.0 – 9.2%). No significant association was observed between the probability of infection and some exposure variables (number of birds present, housing type, poultry type, depopulation method, period during epidemic)

Hsp70 as a candidate subunit vaccine for paratuberculosis

This thesis focuses on vaccination-based control of bovine paratuberculosis, a chronic mycobacterial infection of the small intestine. Bovine paratuberculosis is a highly prevalent disease affecting ruminants worldwide, leading to substantial economic losses. There are concerns that the causative agent is involved in the pathogenesis of human Crohn’s disease, a debilitating inflammatory bowel disease. Therefore, dairy industries have installed national programs to limit human exposure via consumer products, like milk and cheese. Control programs for paratuberculosis are in need of an effective vaccine, however currently there is no vaccine registered for use in cattle in the EU. This thesis evaluates a candidate subunit vaccine, based on recombinant mycobacterial Heat shock protein 70, against bovine paratuberculosis for efficacy, safety and ability to differentiate vaccinated animals from infected animals. Young calves, most susceptible to acquire infection with Mycobacterium avium subspecies paratuberculosis (MAP), often get infected shortly after birth, before a classical vaccine can offer a protective response. Therefore, a vaccine is needed that also has efficacy in exposed animals, so called therapeutic vaccination. It was shown that vaccination of chronic naturally MAP infected cows resulted in reduced fecal shedding and prolonged survival in a proportion of animals, which correlated with vaccination-induced Hsp70 antibodies. Analysis of the Hsp70 vaccination-induced immune response revealed that the B cell response was dominant above Th1 reactivity. Vaccination-induced antibodies can bind Hsp70 in the cell wall of MAP, and provide a possible explanation for the observed protection. Proteome analysis showed that Hsp70 is an abundant protein identified in tuberculin used for the diagnostic skin test for diagnosing bovine tuberculosis. Surprisingly however, vaccination with Hsp70 did not interfere with diagnosis of bovine tuberculosis by skin testing. Antibody-based assays for paratuberculosis can be adapted by inclusion of Hsp70 in the pre-absorption step to remove cross-reactive proteins and thereby differentiating infected animals from vaccinated animals. Furthermore, it was concluded that the use of the candidate vaccine is safe, based on the observation of limited adverse effects after immunization. These characteristics are important pre-requisites for registration of a new paratuberculosis vaccine. Overall, these results show that the candidate vaccine Hsp70/DDA is safe and does not interfere with diagnosis of paratuberculosis and tuberculosis infected cattle. The efficacy of Hsp70/DDA needs to be improved, for example by combining it with other vaccine components, in order to contribute to paratuberculosis disease control

Resistance to anticoccidial drugs : Alternative strategies to control coccidiosis in broilers

Manuscripts documenting the occurrence of resistance against all commonly used anticoccidial drugs abroad, together with the high incidence of clinical coccidiosis in the field (60-90% of flocks) in the Netherlands, were the reasons to start investigations on the occurrence of anticoccidial drug resistance of Dutch and other European Eimeria spp. field isolates. The results showed a high degree of resistance against most tested anticoccidial drugs. The research performed in this thesis was preceded by an extensive literature review focusing on anticoccidial products and alternative strategies. Based on this literature study one alternative coccidiosis control strategy, namely a mannanoligosaccharide (a prebiotic), was chosen for further experimental studies in broiler chickens. Additionally, two other products i.e. ibuprofen (a non-steroidal anti-inflammatory drug (NSAID)) and a mucolytic enzyme (protease) were also used in experimental research aiming at assessing their anticoccidial potential. Ibuprofen was chosen because as a cyclooxygenase inhibitor it was expected to reduce the pathology of coccidiosis lesions through impairment of the production of prostaglandins, and because it was reported that another NSAID (indometacin) was able to reduce oocyst shedding. The mucolytic enzyme was studied as it was speculated that a protease might block the attachment of Eimeria to the mucus layer through its degradation. In view of the poor anticoccidial effect found in the studies performed with mannanoligosaccharide, ibuprofen and the mucolytic enzyme, further research focused on vaccination against chicken Eimeria, which despite some drawbacks has shown to be highly effective against outbreaks of clinical coccidiosis. Another reason to focus on vaccination was the inefficacy of rotation and shuttle programs to solve the coccidiosis resistance problem, which is explained by the fact that resistance is stable even in the absence of drug selection pressure. A welcome side effect of vaccination is the improved sensitivity of Eimeria spp. field isolates for anticoccidial drugs reported by some researchers. This phenomenon may play a key role in reducing the anticoccidial drug resistance problem. However, large-scale field studies documenting this were lacking. Therefore, the relation between the coccidiosis prevention program (vaccination with a live attenuated anticoccidial vaccine or anticoccidial drugs in feed) and anticoccidial drug sensitivity profiles of Eimeria spp. field isolates for diclazuril and monensin was studied. The results showed that use of vaccination was associated with an increased sensitivity of Eimeria spp. field isolates to anticoccidial drugs. Coccidiosis vaccines could be produced more efficiently if cross protection between Eimeria spp. would be relevant enough to reduce the number of species included in the vaccine and/or reduce the vaccination dose. Therefore, cross protection studies between an E. acervulina vaccine line and E. tenella, and E. maxima were performed. The results showed complete protection against E. acervulina, partial cross protection against E. tenella but no cross protection against E. maxima. The thesis is finalized with a summarizing discussion with conclusions and perspectives for future research

Prediction of porcine male fertility

Life starts with fertilisation. Variation in fertility is caused by both farm and sow related parameters and boar and semen related parameters. Therefore, achieving high fertility is not obvious. Predominantly, artificial insemination (AI) is used for breeding pigs. The advantage of AI is that you can dilute semen from high fertile breeding boars and in this way inseminate many sows. The last years, the pig industry is increased in scale and evaluated in specialisation. Unfortunately there is no golden standard concerning the requirements for qualitative good semen. This thesis handles different semen quality characteristics in relation to fertility, showing that the effect of semen quality characteristics on the variation in fertility is relatively small. These effects seems small, but the economic value in a high producing pig industry is large, with the objective to minimise the variation between farms. Assessing semen quality characteristics objectively and relate them to field fertility leads to an efficient production of insemination doses, which results in an efficient spreading of the genetic genes. Semen motility assessed with CASA (Computer Assisted Semen Analysis) and analysing DNA damage are semen quality parameters which show a relation with fertility, in high fertile breeding boars. The value of these tests is possibly even higher in a population in which less selection is performed, added with other tested parameters from this thesis. The conclusions in this thesis contribute to the development of semen quality assessments which improve the prediction of porcine male fertility

Coagulase-negative staphylococci mastitis in Dutch dairy herds

Mastitis is one of the most important diseases in dairy cattle. Recently, the so-called minor pathogens, of which coagulase-negative staphylococci (CNS) are the most important group of bacteria, has received more attention. This thesis focuses on the role of CNS in udder health of dairy cows. The relevance of CNS is studied in a prevalence study of 49 Dutch dairy herds. Coagulase-negative staphylococci were the most frequently isolated group of bacteria (11% of quarters) and were found in all herds. Control programs such as the “five-point program” seem to be less effective to reduce the prevalence of CNS intramammary infection (IMI). The prevalence of CNS IMI was associated with environmental herd level variables such as source of drinking water not being tap water, housing of dry cows in one group instead of multiple groups, pasturing during the outdoor season, and proportion of stalls contaminated with milk. Identification of CNS at the species level in service laboratories is generally carried out using phenotypic tests. The accuracy of two phenotypic tests, API Staph ID 32 and Staph-Zym, was determined in comparison with identification based on DNA-sequencing. A total of 172 CNS isolates from bovine milk samples were classified into 17 species. The API Staph ID 32 correctly identified 41% and he Staph-Zym 31% of the CNS isolates. Both phenotypic tests were unsuitable for identification of CNS species from bovine milk samples. The effect of CNS on somatic cell count (SCC) of quarter, cow and bulk milk was studied. Quarters with a CNS IMI had a lower SCC than quarters with a major pathogen IMI but a higher SCC than culture-negative quarters. This was also found for composite SCC. Cow-level prevalence of CNS IMI was higher in dairy farms with a BMSC

Bio-economic modeling of bovine intramammary infections

The research of this thesis was directed to support decision making in relation to mastitis control with special focus on the dry period. First, a guideline to cost factors associated with mastitis was set, and a comprehensive literature review was conducted to evaluate literature estimates of the cost and cost-benefits of mastitis control. In another project, a data analysis was conducted to estimate production loss due to new subclinical mastitis in Dutch dairy herds. The estimates were used as input values to assist in developing a dynamic and stochastic bio-economic model of intramammary infection. The model simulated the major pathogens in the Netherlands using recent knowledge on the dynamics of pathogen-specific intramammary infection to calculate the cost of these infections. Two systematic meta-analysis reviews were conducted; the first quantified the preventive effect of dry period interventions against new intramammary infections. The second meta-analysis quantified the cure rate of existing intramammary infections at dry off using dry cow therapy. Subsequently, the bio-economic model was updated to include the dynamics of pathogen-specific intramammary infections in the dry period. Thereafter, an economic evaluation of applied dry period interventions was carried out based on the meta-analyses studies

Consequences of intermittent suckling for performance in the pig

In Europe, piglets are usually weaned before 4 weeks of age, thus changing abruptly from highly digestible milk to a less digestible starter diet, resulting in reduced feed intake and growth after weaning and sometimes post weaning diarrhea. Intake of a sufficient amount of creep feed during lactation can reduce these post weaning problems, but creep feed consumption is usually low and highly variable. This thesis describes the effect of intermittent suckling (IS; a management technique in which piglets are separated from the sow for 12 h/ day from d 14 to weaning (d 25), on performance of pigs before and after weaning. IS increased average creep feed intake during lactation. Distribution of creep feed intake shifted from a skewed one, with a majority of litters consuming less than 250 g.piglet-1 in control litters, to a normal distribution with an average creep feed intake of 500 to 750 g.piglet-1 in IS litters. The higher creep feed intake caused by IS resulted in better performance after weaning: IS litters had higher feed intake and higher weight gain in the first two weeks after weaning. Thereafter no differences were found until slaughter. IS litters with little or no creep feed intake during lactation tended to have higher weight gains and feed intake after weaning than control litters with comparable creep feed intake during lactation. IS did not increase the percentage of eaters within a litter during lactation and weaning weights did not differ between eaters and non-eaters. From one until four weeks after weaning piglets that were eaters during lactation had higher weights than non-eaters. IS did not affect feeder visiting behaviour of piglets from litters with an anyhow high level of feed intake during lactation, but IS piglets from litters with a low level of feed intake were stimulated to visit the feeder during lactation, which probably made them already familiar with the feeder and the feed. Part of the variation in feed intake between litters might be explained by differences in suckling behaviour and activity. To investigate if IS and/or creep feed intake affects the absorptive capacity of the small intestines, an in vivo small intestine segment perfusion test was performed in 24 newly weaned piglets (6 eaters and 6 non- eaters from each treatment). Net absorption in non-infected segments of the small intestine was significantly higher in eaters than in non-eaters. No difference was found between IS and control piglets. IS also affected the sows: weight loss during lactation was decreased and ovulations were advanced. The results of these studies demonstrate that IS improves both creep feed intake during lactation and feed intake and weight gain after weaning. Piglets consuming creep feed during lactation had higher weights and net absorption in the small intestine after weaning, independent of the suckling regimen. IS was especially efficient in piglets from low feed intake litters; these piglets were stimulated to investigate the feeder during lactation, which facilitated consumption of feed after weaning