Prevalence and etiology of subclinical mastitis in intensively managed flocks and related changes in the yield and quality of ewe milk

A total of 1140 milk samples from 380 randomly selected Comisana ewes, in parities 1-6, were collected aseptically during early-, mid- and late-lactation from five intensively managed flocks located in the Apulia region, southern Italy. All flocks were housed on straw litter in prefabricated buildings, were given hay and pelletted concentrates and were milked twice daily using pipeline milking machines. Individual milk samples were analyzed for composition, renneting parameters and somatic cell count (SCC), and cultured for mastitis related pathogens. No cases of clinical mastitis were detected. Mean incidence rates were 8.4, 5 and 4.1%, respectively, for infectious (bacteriologically positive milk samples with >10(6) somatic cells/ml), latent (bacteriologically positive milk samples with <3 x 10(5) somatic cells/ml) and non-specific subclinical mastitis (bacteriologically negative milk samples with >10(6) somatic cells/ml). Environmental pathogens, primarily E. coli, were largely predominant in the mills from infected ewes and markedly increased with the advancement of lactation. Reduction in ewe milk yield and deterioration of mills quality and renneting ability were more marked in infectious and non-specific than in latent mastitis cases, whereas various kinds of pathogens had a similar impact on milk yield and composition. The low incidence of contagious pathogens suggests that, in intensive production systems, ewe udder health may benefit from more efficient control of sanitation of milking practices and equipment. The high prevalence of environmental and opportunistic micro-organisms also indicates that poor ambient hygiene and exposure of ewes to environmental and management stressors must be regarded as the main risk factors for udder infections. (C) 2002 Elsevier Science B.V. All rights reserved.