Anthelmintic resistance
Farming sustainably can mean many different things, but the continued ability to control nematode parasites is perhaps one of the starkest examples of where planning for long-term sustainability is essential if we are to continue to maintain livestock outputs. Resistance to the benzimidazole and macrocyclic lactone anthelmintics is widespread in Cooperia on cattle farms in New Zealand. Since this was first documented in 2006, little has changed except for the widespread use of levamisole to control Cooperia in young cattle. A study by Sauermann et al (2024) (https://doi.org/10.1016/j.vetpar.2023.110079) reports the emergence of simultaneous resistance to the benzimidazole, macrocyclic lactone and levamisole anthelmintics in Cooperia and in Ostertagia. Anthelmintic efficacy against nematode parasites of cattle was investigated on four commercial farms following reports of poor animal growth rates and welfare, and positive faecal egg counts, despite routine treatment with combination anthelmintics, which included levamisole. Actives tested varied between farms but always included levamisole alone and several combination products containing levamisole. Of the 20 tests conducted, only 3 exceeded 90% efficacy against Cooperia, even though 8 of the products tested were combinations containing levamisole and at least one other broad-spectrum anthelmintic. Levamisole used alone achieved efficacies between 44% and 71% against Cooperia across the four trials. The only product to exceed 95% efficacy against Cooperia was a combination of monepantel and abamectin which was 100% effective against all parasites. Resistance to oxfendazole in Ostertagia was indicated on three farms, while on one farm efficacy of all the tested products was ≤75% against this parasite. The results clearly demonstrate the emergence of simultaneous resistance to oxfendazole, levamisole and the macrocyclic lactone anthelmintics. Despite years of advice and recommendations to change farming practices, many farmers are now faced with the possibility of being unable to control cattle parasites.
Colostrum
The objectives of a study by Röder et al (2023) (https://doi.org/10.3168/jds.2023-23467) were to evaluate different analytical methods to determine colostrum quality in dairy cattle, including one laboratory-based method (ELISA) and 4 on-farm tests. They hypothesized that the colostral IgG concentration using different analytical methods, such as ELISA (mg/mL), digital Brix refractometer (% Brix), colostrometer (specific gravity and mg/mL), an outflow funnel (seconds), and a lateral flow assay (mg/mL), were highly correlated with the reference method, radial immunodiffusion (RID; mg/mL) and would generate comparable results. Colostrum samples were collected from 209 Holstein Friesian cows on two commercial dairy farms. Colostrum weight and colostrum temperature were measured. Test characteristics, such as optimum thresholds, sensitivity, specificity, and area under the curve (AUC) were determined using receiver operating characteristic curve analyses for each test. Out of 209 colostrum samples assessed by RID, 186 (89%) samples had high quality (≥50 mg IgG/mL), while 23 colostrum samples (11%) showed poor quality with IgG concentrations <50 mg/mL. The mean IgG concentration (+/− SD) was 101.3 +/− 45.9 mg/mL and the range 6.0–244.3 mg/mL. The Pearson correlation coefficient between RID and ELISA was 0.78. In comparison to RID, Pearson correlation coefficients for the on-farm tests were: 0.79 (digital Brix refractometry), 0.58 (colostrometer: specific gravity), 0.61 (colostrometer: temperature corrected), 0.26 (outflow funnel) and 0.43 (lateral flow assay), respectively. The optimal threshold to identify high-quali-ty colostrum using ELISA was 50.8 mg/mL with sensitivity 91.3%, specificity 92.3%, and AUC of 0.94. For the on-farm tests, sensitivity ranged from 95.7% (Brix refractometry) to 60.9% (lateral flow assay). Specificity ranged from 88.6% (lateral flow assay) to 75.9% (colostrometer: temperature corrected). The AUC ranged from 0.93 (Brix refractometry) to 0.73 (outflow funnel). Based on the AUC, ELISA (0.94) and Brix refractometry (0.93) can be considered highly accurate, but among on-farm tests only the digital Brix refractometer and the colostrometer were adequate to determine colostrum quality.
Milk fever
An open access perspective piece by Hernandez and McArt (2023) (https://doi.org/10.3168/jds.2023-23355) offers insight into recent thinking around postparturient hypocalcaemia. Milk fever is caused by calcium (Ca) expenditure at the initiation of lactation, so severe that cows can die if left untreated. Fortunately, through prepartum nutritional improvements, this version of clinical hypocalcaemia is now relatively rare. Nonetheless, the opinion that all versions of postpartum hypocalcaemia are detrimental remains pervasive, which is particularly significant given that 50% of cows are subclinically hypocalcaemic after calving. This has led to a variety of management and treatment strategies, ranging from prepartum dietary programmes to postpartum Ca gels and boluses, targeted at preventing hypocalcaemia. Recent research has determined that postpartum dairy cows can experience different types of subclinical hypocalcaemia: transient, persistent or delayed. It is recognised that cows experiencing transient hypocalcaemia as part of the homeorhetic adaptation to lactation are the highest milk producers in modern dairy herds, whereas cows with hypocalcaemia several days after calving experience disease and losses in milk production. Therefore, it is wrong to assume all postpartum hypocalcaemia is detrimental and that treatment of all cases is considered necessary and beneficial. Cows differ in their ability to manage this phenomenon, and it is possible that immediate postpartum influences such as dry matter intake, inflammation and immune activation affect appropriate Ca regulation in the days following calving.