Risk factors of high somatic cell count and differential somatic cells in early lactation associated with selective dry cow therapy

• Published in: Animal (Cambridge, England) England), 2023-10, Vol.17 (10), p.100982-100982, Article 100982
• Main Authors: Mondini, S., Gislon, G., Zucali, M., Sandrucci, A., Tamburini, A., Bava, L.
• Format: Article
• Language: English
• Subjects: Dairy cattle; Dry period management; Hygiene Score; Logistic regression; Milk leucocyte
• ISSN: 1751-7311; 1751-732X
• DOI: 10.1016/j.animal.2023.100982

•A selective dry cow therapy was applied in three dairy cattle farms.•Selective dry cow therapy was based on total and differential somatic cell count.•Somatic cell count and percentage of neutrophils in milk were related.•The reduction of intramammary antimicrobials use at dry-off is possible.•High somatic cell count and no antibiotic at dry-off are risk factors for high somatic cell count after calving. The routine use of intramammary antimicrobial products in all dairy cows at the beginning of the dry period is no longer allowed in European Union (EU) countries due to the new Regulation (EU) 2019/6 to reduce antimicrobial resistance. This study investigated the application of a selective dry cow therapy scheme and the risk factors of high individual milk somatic cell count (SCC) and individual neutrophil count in early lactation, as a response to the application of a selective dry cow therapy (SDCT) protocol. The study was carried out on three commercial farms, and a total of 243 lactating cows were monitored at the end of lactation and at the beginning of the next one, 91 of which were dried off without the use of antimicrobials (NoT) based on milk SCC, differential somatic cell count (DSCC), and the response of Vetscan DC-Q milk analyser, using a secret algorithm. The remaining 152 cows received antimicrobials (T). After calving, similar means were observed between the two treatment groups for SCC (4.8 vs 4.9 log10 cells/ml for T and NoT, respectively, P = 0.5) and total milk leucocyte count (TLC) (5 vs 5.1 log10 cells/ml for T and NoT, respectively, P = 0.7) in milk. However, the use of antimicrobials led to a lower DSCC (58 vs 64% for T and NoT, respectively, P = 0.01) and lower percentage of neutrophils (59 vs 64% for T and NoT, respectively, P = 0.05), although the levels of DSCC and percentage of neutrophils in cows dried off without antimicrobials remained lower than the risk threshold suggested by the international literature. A logistic regression was computed after the application of selective dry cow therapy to identify risk factors of high milk SCC (≥100 000 cells/mL) at the beginning of lactation. Increased milk SCC after calving was related to high SCC at the end of lactation and abandonment of antimicrobial therapy at dry-off. Moreover, the length of the dry period, milk protein content, and flank cleanliness in the last test day before dry-off were other factors in the logistic regression. Neutrophil counts at the beginning of the next