Use of approved cefazolin based intramammary dry goat treatment and its effects on the milk microbiota

Intramammary dry-off treatment is widely considered an effective method for preventing and curing intramammary infection (IMI) in lactating cows; however, it is not commonly used in small ruminants like goats. Therefore, this study was designed to evaluate the effect of an approved cefazolin-based intramammary treatment on the milk microbiota of Alpine dairy goats during the dry and early lactation periods. Sixty goats were randomly selected based on bacteriological results and randomly allocated into the control group (CG) or the treatment group (TG). Cefazolin 250 mg (Cefovet A, Dopharma, Firenze, Italy) was administered to the TG group at dry-off, whereas the CG received no treatment. Pooled milk samples were collected at dry-off (T1; 52 samples), colostrum (T2; 46 samples), and 5-10 days in milk (T3; 55 samples) for bacteriological analysis, somatic cell count (SCC), and 16 S rRNA gene sequencing. SCC levels were initially high in both groups at T1 (TG: 1,588,000 cells/mL; CG: 1,629,000 cells/mL), which significantly decreased at T3 (TG: 148,000 cells/mL; CG: 153,000 cells/mL). Notably, the TG had fewer infected mammary glands than the CG at T3 (p = 0.0248), while no differences were found at T1 or T2. Despite the reduction in SCC and infection rates, cefazolin-based treatment did not significantly affect the alpha- and beta-diversity between the TG and CG. On the other hand, shifts in microbial composition, including fluctuations in Firmicutes, Proteobacteria, and Actinobacteria, were primarily due to the lactation stage rather than the treatment. Differential abundance analyses identified non-pathogenic genera, such as Acinetobacter, Bacteroides, and Paracoccus, that varied between groups at different timepoints. The study provided insights into the effects of cefazolin-based dry goat treatment on goat milk microbiota and its changes during the lactation cycle, demonstrating its potential to reduce SCC and mammary gland infections without significant alterations to the milk microbiota.