Effect of the Selective Dry Cow Therapy on Udder Health and Milk Microbiota

Abstract

Recently, the use of antimicrobials on dairy farms has been significantly limited from both the legislative and consumer points of view. This study aims to check the efficacy of selective dry cow therapy (SDCT) versus blanket dry cow therapy (BDCT) on bovine udder in healthy animals. SDTC is when an antibiotic is administered only to infected cows, compared with BDCT, where all cows receive an antimicrobial, regardless of their infection status. The milk samples were collected from enrolled Holstein Friesian cows 7 days before dry-off (T0) and 10 days after calving (T1) to assess somatic cell count (SCC), intramammary infections (IMIs), and milk microbiota variation. After pre-drying sampling, cows are randomly assigned to the following treatments: internal teat sealant alone (ITS; 24 cows), which is a treatment in a cow that does not receive antibiotics in SDTC, or in combination with intramammary antibiotic treatment (A+ITS; 22 cows). Non-statistically significant results are found between the two treatment groups at T1 for SCC, milk yield, and alpha diversity in milk microbiota. A statistically (p < 0.033) T1 IMI decrease is reported in the A+ITS group, and a significant beta diversity analysis is shown between the two timepoints (p = 0.009). This study confirms the possibility of selective drying without new IMI risk or increased SCC at calving, considering healthy cows without contagious infections and SCC values >200,000 cells/mL in the previous lactation.

Keywords: cattle; milk microbiota; one health approach; selective dry cow therapy.

Figure 1

Bar plot of phylum relative abundances in the dairy cow milk microbiome over time, per treatment. Only phyla with overall relative abundance >0.5% are included.

Figure 2

Bubble plot of the average relative abundances per class, order, family, and genus. Only taxa with average relative abundance ≥1%.

Figure 3

Bar plot of significantly different OTUs between treatments p < 0.05, at dry-off and after calving. In (A), the p-value is reported: darker colors correspond to lower p-values (higher significance). In (B), the antibiotic-teat sealant difference in terms of OTU counts is reported. Blue/orange bars indicate the differences in normalized microbial counts between ITS+A and ITS, positive (blue) or negative (orange).

Figure 4

First two dimensions from the (non-metric) multi-dimensional scaling of the Bray–Curtis dissimilarity matrix. Samples were grouped by treatment within timepoint: before dry-off (T1) above, 10 days after calving (T2), below. From PERMANOVA (999 permutations): there were not any statistically significant differences between treatment (p-value = 0.824) and between the timepoint–treatment interaction (p-value = 0.812). A statistically significant difference was detected for the analysis of beta diversity for the timepoints with a p-value = 0.0092955.

Figure 5

The study design. Inclusion criteria were no clinical mastitis and an average SCC lower than 200,00 cells/mL taken from dairy herd improvement (DHI) data. Eligible cows for these criteria were milk sampled seven days before dry-off (T0) in order to detect the absence of major pathogens causing mastitis and be definitely enrolled in the study. Enrolled cows were randomly assigned to the dry-off treatment group, with internal teat sealant alone and combined with antibiotics. Ten days post-partum (T1), a second milk sample was collected, and cows were monitored until 100 days in milk (DIM) for the onset of clinical mastitis.