Prevalence of udder pathogens in milk samples from Norwegian dairy cows recorded in a national database in 2019 and 2020

Table 2 Distribution of bacterial culture results in bovine milk samples in Norway (n = 36,431) analysed years 2019–2020

	Definition of cow-level diagnosis
Bacterial finding	Definition 1^a		Definition 2^b		Definition 3^c
	n	%	n	%	n	%
Negative^d	7743	21.2	7743	21.3	7743	30.1
Major pathogens
Staphylococcus aureus	8918	24.5	7750	21.3	5028	19.6
Streptococcus dysgalactiae	4827	13.3	3618	9.9	2105	8.2
Streptococcus uberis	3269	9.0	2365	6.5	1411	5.5
Escherichia coli	1859	5.1	1493	4.1	936	3.6
Trueperella pyogenes	758	2.1	503	1.4	346	1.4
Streptococcus agalactiae	311	0.9	311	0.9	162	0.6
Mixed major^e	–	–	2244	6.2	–	–
Minor pathogens
Staphylococcus epidermidis	3630	10.0	1790	4.9	1327	5.2
Staphylococcus chromogenes	2180	6.0	1022	2.8	766	3.0
Staphylococcus simulans	1697	4.7	704	1.9	508	2.0
Staphylococcus haemolyticus	670	1.8	277	0.8	195	0.8
Other non-aureus staphylococci^f	5917	16.3	2647	7.3	2237	8.7
Corynebacterium bovis	3418	9.4	903	2.5	901	3.5
Mixed minor^g	–	–	907	2.5	–	–
Other bacteria^h	–	–	974	2.7	870	3.4
Contaminationⁱ	2264	6.2	1180	3.2	1163	4.5
Total	47,461	1305^j	36,431	100	25,698	100

^aDefinition 1: Each quarter sample diagnosis was included independent of the other quarter samples, meaning that cows with two different diagnoses at the same sampling occasion contributed to the frequency of both udder pathogens
^bDefinition 2: Cows with at least one quarter with S. aureus, S. dysgalactiae, S. uberis, E. coli, T. pyogenes or S. agalactiae (“major” pathogens) were assigned this as cow-level diagnosis. Cows were given the cow-level diagnosis NAS, S. epidermidis, S. chromogenes, S. simulans, S. haemolyticus or C. bovis (“minor pathogens”) if they had no major udder pathogen at the same sampling event
^cDefinition 3: Cow-level diagnoses in a subset with only one bacterial finding per sampling event
^dNo growth in all sampled quarters
^eCows with more than one major udder pathogen at the same sampling event
^fNon-aureus staphylococci other than S. epidermidis, S. chromogenes, S. simulans, S. haemolyticus
^gCows with more than one minor udder pathogens at the same sampling event
^hBacteria other than presented in the table
ⁱSamples with at least one quarter yielding more than two different colony types and no other udder pathogens in other quarters
^jGiving on average 1.3 bacterial diagnoses per cow per sampling event

ISSN: 1751-0147