title: Somatic cell count status across the dry period as a risk factor for the development of clinical mastitis in the subsequent lactation.
abstract: The objective of this study was to determine the risk of clinical mastitis in the first 120 d in lactation based on previous somatic cell count (SCC) history in a herd with a very low prevalence of contagious pathogens. A total of 218 cows from a university herd were enrolled at dry-off. Duplicate quarter milk samples were collected from all quarters at dry-off, postcalving (2 to 9 d in milk), and before treatment of all first cases of clinical mastitis that occurred during the first 120 d of the subsequent lactation. Quarter SCC statuses across the dry period were defined based on comparison of quarter SCC between the date of dry-off and the postcalving sampling periods. The relationship between the probability of developing clinical mastitis in the first 120 d of lactation and SCC status across the dry period and other explanatory variables was assessed using logistic regression. In the first 120 d postcalving, 68 first cases of clinical mastitis occurred in 47 cows. Of quarters that experienced a microbiologically positive clinical case, the same microorganism was never isolated from milk samples obtained at dry-off or consistently isolated from milk samples collected at all sampling periods. Coagulase negative staphylococci were the most prevalent pathogens isolated from subclinical intramammary infection, whereas gram-negative pathogens were the most common pathogen associated with clinical cases. Quarters that had at least 1 case of mastitis during the previous lactation were 4.2 times more likely to have a first case of clinical mastitis in the current lactation than quarters that did not have clinical mastitis in the previous lactation [odds ratio (OR) = 4.2 (1.8, 10.0)]. Quarters of cows of greater than fourth parity were 4.2 times more likely to have a first case of clinical mastitis than quarters of cows of second parity [OR = 4.2 (1.4, 10.0)]. Quarters with SCC > or =200,000 cells/mL at dry-off and postcalving were 2.7 times more likely to experience a first case of mastitis than quarters with SCC <200,000 cells/mL at both periods [OR = 2.7 (0.97, 7.67)].
authors.affiliation: Department of Dairy Science, University of Wisconsin, Madison 53706, USA.
authors.forename: J C F
authors.initials: JC
authors.lastname: Pantoja
authors.forename: C
authors.initials: C
authors.lastname: Hulland
authors.forename: P L
authors.initials: PL
authors.lastname: Ruegg
mesh_terms: D000818:Animals; D001424:Bacterial Infections / Q000453:epidemiology / Q000382:microbiology / Q000662:veterinary*; D018407:Bacterial Physiological Phenomena; D002417:Cattle; D002452:Cell Count; D005260:Female; D007774:Lactation / Q000502:physiology*; D016015:Logistic Models; D008414:Mastitis, Bovine / Q000453:epidemiology* / Q000382:microbiology; D008892:Milk / Q000166:cytology* / Q000382:microbiology; D011247:Pregnancy; D015995:Prevalence; D012307:Risk Factors; D016019:Survival Analysis; D014922:Wisconsin / Q000453:epidemiology