Inge M. G. A. Santman-Berends

In 2023, bluetongue serotype 3 (BTV-3) emerged in the Netherlands, leading to a 19% prevalence of BTV antibodies in animals by spring 2024. This highlighted the urgent need for vaccination, which became available in May 2024. Despite this, BTV-3 spread extensively throughout 2024, causing farmers to perceive the vaccination as ineffective. High-quality census data on key health parameters from the cattle monitoring system were used to evaluate the impact of BTV-3 vaccination during the 2024 epidemic. Data were available for ~13,500 dairy herds from January 2020 to September 2024. Data included information on mortality, milk production, BTV-3 antibody status in the spring of 2024, and BTV-3 vaccination status. Herds were classified by BTV-3 status (no antibodies, low or high antibody levels) combined with the herds' vaccination status, for example, unvaccinated, fully but not timely vaccinated, or fully and timely vaccinated, to determine BTV-3 susceptibility at the start of the BTV-3 epidemic in 2024. Timely vaccination was defined as the full completion of herd immunization before BTV-3 began to spread in the area where the herd was located. Generalized estimated equations were used for analysis, with 4-wk moving average mortality per age category of cattle or average weekly milk production (kg/cow per d) as dependent variables. Mortality and milk production in vaccinated herds during the BTV-3 epidemic in 2024 were compared with (i) the period in which BTV-3 was not yet present and (ii) mortality and milk production in unvaccinated herds during the BTV-3 epidemic. Other explanatory variables included herd size, location (province), season, herd health status for several endemic diseases, and time trends. Herd and week were included as time series variables. Mortality in cows (≥2 yr) was significantly increased in all herds compared with mortality in BTV-3-free years. However, during the BTV-3 epidemic in 2024, mortality in fully and timely vaccinated herds was significantly lower compared with mortality in unvaccinated herds, with an incidence rate ratio (IRR) of 0.77 (95% CI: 0.67-0.89). Youngstock and calf mortality in fully and timely vaccinated herds did not significantly differ from the period herds were classified as BTV-3 free. During the BTV-3 epidemic in 2024 in unvaccinated herds, postnatal calf mortality (≤14 d old) increased with an IRR of 1.58 (95% CI: 1.49-1.67), preweaning calf mortality (15-55 d old) with an IRR of 1.28 (95% CI: 1.17-1.40), weaned calf mortality (56 d-1 yr old) with an IRR of 1.22 (95% CI: 1.08-1.38), and youngstock mortality increased with an IRR of 1.53 (95% CI: 1.32-1.76) compared with the period in which herds were classified as BTV-3 free. In addition, fully and timely vaccinated herds without naturally acquired antibodies had a 1.00 kg higher milk production per cow per day (95% CI: 0.40-1.61), and fully and timely vaccinated herds with high naturally acquired antibody levels had a 1.23 kg higher milk production per cow per day (95% CI: 0.63-1.91), compared with unvaccinated herds with a similar antibody status. In conclusion, vaccination significantly mitigated the impact of BTV-3 in 2024 in the Netherlands when cattle were fully and timely vaccinated.

In September 2023, bluetongue virus serotype 3 (BTV-3) emerged in the Netherlands for the first time. To be prepared for a potential resurgence in 2024, a study was performed during early spring 2024, considered as a low-risk period, to estimate the prevalence of BTV-3 and identify associated risk factors in Dutch dairy cattle. Between December 2023 and April 2024, bulk tank milk (BTM) samples from 12,756 dairy herds were tested to estimate the herd-level and within-herd antibody prevalence. Additionally, an online survey was distributed to participating farmers to collect farm management information from 2023. Animal movement data were obtained from the national identification and registration database. Multivariable logistic regression was performed to quantify associations between potential risk factors and the probability of BTV-3 infection. Herd-level prevalence was 64% (95% CI: 63%-65%). Assuming that BTM test results provide a reliable indication of within-herd prevalence, the expected within-herd prevalence was 36% (95% CI: 35%-37%) in antibody-positive herds. Using BTM as a proxy for within-herd prevalence, the nationwide cow-level prevalence was estimated at 19% (95% CI: 19%-20%). For 5,253 dairy herds, both prevalence data and survey data were available. Factors associated with a lower odds of the presence of BTV-3 antibodies in bulk milk included the presence of large ventilation openings and use of mechanical ventilation while cattle were housed indoors. Factors associated with higher odds included grazing (both limited and longer periods), introduction of cattle from BTV-3 high-risk areas, presence of sheep on the farm, and the month of first BTV notification in the herd's postal code area. No association was found between the use of insecticides and the presence of antibodies. This study shows that although the herd level prevalence after the first BTV-3 epidemic season was substantial, cow-level prevalence at the national level was still relatively low, leaving a large population of cattle susceptible for BTV-3 in 2024. In addition, several management factors were identified, which inform preventive strategies to reduce the risk and the impact of future BTV-3 infections in dairy herds.

Optimising kid rearing is essential for sustainable dairy goat farming, yet validated parameters and practical benchmark data are lacking. This study aimed to develop and evaluate a set of key performance indicators (KPIs) for monitoring kid-rearing practices through a participatory approach. Researchers, veterinarians and five dairy goat farms participated developed a prototype set of KPIs covering birth, colostrum management, average daily gain (ADG), and mortality, which were stratified across four rearing phases: perinatal (first 48 h), postnatal (birth to weaning), postweaning (weaning to 12 weeks), and final rearing (12 weeks to mating). The set of KPIs was subsequently tested for its added value but also for its feasibility in practice on the five participating farms as proof of principle. On these farms, data were gathered over a six-month period (June 2020–January 2021), combining routine census data with on-farm records. Only three out of five farms returned complete datasets encompassing data from 715 kids. Results revealed significant variation in rearing outcomes across farms, particularly in birth weights and postweaning growth. Birth weight emerged as a key predictor for ADG, while differences in weaning strategies had the greatest impact on postweaning performance. Although the farmers acknowledged the added value of the developed KPIs, collection of these data during the kidding season was challenging and required further automation to simplify data collection on the farm. This study demonstrates the feasibility and value of individual-level data collection in dairy goat systems and underscores the need for practical tools to support routine monitoring and data-driven management.

Summary: After highly pathogenic avian influenza (HPAI) virus was detected in dairy cows in the United States, concerns were that infections could have occurred in Dutch cattle despite having an effective monitoring and surveillance system. A total of 2,190 archived cattle serum samples from 367 different herds collected between January 2022 and February 2024 were selected risk-based for testing. Although 4 samples initially tested positive in an influenza A blocking enzyme-linked immunosorbent assay (ELISA), a confirmatory Luminex H5/H7 assay showed that none of the samples had antibodies against H5, H7, and N1 to N9. The positive results in the ELISA were likely false positive. In conclusion, there is no indication that HPAI virus subtype H5N1 has circulated in cattle in the Netherlands between 2022 and 2024. This aligns with the absence of any indication for clinical cases in Dutch cattle over recent years in the national monitoring and surveillance system.

The duration of excretion of dry cow antimicrobials is hard to predict and therefore the level of antimicrobial residues in colostrum can differ considerably between cows. The feeding of colostrum with antimicrobial residues to newborn calves may lead to antimicrobial resistance in calves. The aim of this study was to quantify the prevalence and residue level of dry cow antimicrobials in colostrum from dairy cows. Additionally, the association between antimicrobial residues in colostrum and the prevalence of extended spectrum and AmpC β-lactamaseproducing Escherichia coli (ESBL/AmpC-EC) in colostrum and in the feces from young dairy calves was evaluated. The work described in this paper consists of 3 studies. In the first study, in 75 of 118 colostrum samples antimicrobial residues were found, in 50 of 88 β-lactam treated cows, and in 25 of 30 cows treated with a combination of an aminoglycoside and a β-lactam. In cows that had been dried off with a combination of an aminoglycoside and a β-lactam, in significantly more samples antimicrobial residues were found. In 38 of the colostrum samples tested, antimicrobial concentrations (mainly cloxacillin) exceeded the Maximum Residue Limit. The prevalence of antimicrobial positive colostrum samples presented was much higher than earlier described. In the second study 28 dairy cows from 8 farms were dried off with either cloxacillin or a combination of neomycin and benzylpenicillin. Because in study 1 the tendency of a negative association was found between the use of teat sealants and the presence of antimicrobials in colostrum, it was hypothesized that with the striping of the teat sealant much of the antimicrobial residues was removed. This hypothesis could not be confirmed by comparing antimicrobial concentrations in the first streams of the first milking and the remainder of that milking. The 22 clocaxilin treated cows were followed up for 6 subsequent milkings, during which a decrease in the concentration of antimicrobial residues was found. In the third study, 87 cows from 10 herds were included of which 58 cows were dried off with cloxacillin while 29 cows were dried off without antimicrobials. Cows were compared with respect to antimicrobial residues in the first 5 milkings after calving and the occurrence of ESBL/AmpC-EC in the feces from their calves, collected at d 1, d 7 and d 14 of life. Significantly higher percentages of ESBL/AmpC-EC positive samples were found in feces samples collected at d 7 and d 14 compared with the d 1 samples. No significant differences were found in the prevalence of ESBL/AmpC-EC positive fecal samples between calves born from cows that had been dried off without antimicrobials and those that had been dried off with cloxacillin. Given the fact that cloxacillin does not select for ESBL/AmpC-EC, this was not unexpected. This study showed that colostrum from cows dried off with antimicrobials often contains antimicrobial residues. Although no effect of these residues on the prevalence of ESBL/AmpC-EC in fecal samples of calves was found in this study, we recommend to minimize antimicrobial use at drying off and to respect withdrawal recommendations.

Since 2018, Dutch dairy farmers are obliged to opt for one of 4 routes to achieve BVDV freedom in the national BVDV eradication program. This observational study evaluated efficacy of the total BVDV program using indicators such as number of persistent infected cattle (PI's), percentage of dairy herds with a BVDV-free status, percentage of BVDV-free dairy herds with evidence of introduction of BVDV and, as well as a cost calculation per route. The Dutch BVDV program appeared to be successful as the percentage of BVDV-free dairy herds increased from 59 percent at the start of the program to 89 percent by the end of 2023. The number of PI's detected each quarter, declined from 500 PI's in the third quarter of 2019 to 83 PI's in the last quarter of 2023. The percentage BVDV-free dairy herds with evidence of (re)introduction of BVDV decreased from 1.29 percent per quarter in the first year of the mandatory program to 0.25 percent per quarter by the end of 2023. In Europe, BVDV control program designs are often tailored to the country's specific situation e.g., prevalence at the start of eradication, risk profile of a country or herd, desired speed of eradication and available funds. These results show that the Dutch approach in which multiple routes can be followed toward BVDV freedom is successful.

Monitoring and surveillance of pathogens are crucial for safeguarding animal and public health. While passive surveillance is more common for wild and free‐living animals, active monitoring improves the detection and characterisation of specific pathogens relevant to animal and public health. In the Oostvaardersplassen (OVP) nature reserve in the Netherlands, an active monitoring system for Heck cattle ( Bos taurus ), Konik horses ( Equus caballus ) and red deer ( Cervus elaphus ) has been in place since 1997. This study utilised the data generated from the monitoring system to estimate pathogen prevalence and to evaluate the ongoing monitoring efforts. Yearly prevalences were calculated for each observed pathogen, and probability of freedom from infection was assessed for pathogens that were not detected. In cattle, the highest antibody prevalences (>35%–50%) were observed for Bovine herpesvirus 1 (BoHV‐1), Bluetongue virus (BTV), Schmallenberg virus (SBV) and Fasciola hepatica , whereas lower (Coxiella burnetii , Mycobacterium avium subsp. paratuberculosis ( MAP ), Salmonella spp. and S . Dublin. Similar pathogens were observed in red deer and cattle, but prevalences were generally lower in red deer. In horses, Equine herpesvirus 1 and 4 (EHV‐1 and 4), Salmonella spp., S . Dublin and S . Typhimurium were detected. Bovine leukaemia virus (BLV), Brucella abortus , Mycobacterium bovis (bTB) and Leptospira interrogans serovar Hardjo were not detected in cattle and red deer, nor were Equine infectious anaemia virus (EIAV), Equine influenza virus (EIV) and West Nile virus (WNV) observed in horses. Most of the detected pathogens are endemic in the Netherlands, while non‐detected pathogens often have an official disease‐free status. This study provides valuable insights into pathogen presence in free‐living large herbivores at the OVP nature reserve. The current monitoring system is highly valuable and its effectiveness can be further enhanced through improvements, such as increased sampling efforts and pathogen prioritisation. This knowledge could guide the implementation of similar monitoring strategies in nature reserves across Europe.