Staphylococcal Dissemination During the Milking Procedure in Sheep Flocks

The general objective of this work was the evaluation of the potential for dissemination of staphylococci within the milking system during the actual milking procedure in dairy sheep flocks. Specific objectives of the study were i) the evaluation of bacterial recovery from samples from ewes (teat duct material, milk) collected before and after milking and ii) the description of sources of potential dissemination of staphylococci to ewes during the milking procedure and iii) the identification of associations related to the milking routine for increased dissemination of staphylococci. Four dairy sheep farms with a total of 690 ewes were enrolled into the study and visited thrice, on the 2nd-3rd, 12th-15th and 22nd-27th week of the lactation period. In the milking parlour, three different teatcups were selected at random and swab samples were obtained from these, as well as from the mammary glands milked into these teatcups before and after completion of milking; in total, samplings were performed on 420 occasions in the three visits. Dissemination was defined when all isolates considered to be implicated in a chain (teat duct to teatcup to teat duct of subsequent ewes) were identified similarly at species level. Dissemination sources (milk, teat duct material) were considered for potential dissemination to subsequent dissemination targets (teatcups, teat ducts). The proportion of dissemination incidents during the milking procedure was considered and associations were evaluated. There were shifts in status in bacterial isolation in both 'directions' (i.e., '' ⟼ '+', '+' ⟼ ''), as well as samples that maintained original bacteriological status (i.e., '+' ⟼ '+', '' ⟼ '') for both teat duct material and milk. A significantly higher proportion of teatcups from which bacteria were recovered during the milking procedure, was recorded during the second visit to the farms (85.0%) (p < 0.0001). In total, 111 incidents of dissemination of staphylococci were recorded, of which a higher proportion was seen also during the second visit to the farms (38.9%) (p < 0.0001). In univariable analysis, the decreasing ambient temperature within the parlour during the milking procedure emerged with a significant association with the proportion of dissemination of staphylococci (p = 0.0003). The study highlighted a tendency for bacterial flushing from mammary glands during the milking procedure, which may contribute to reduction of potential intramammary infections. However, the bacterial flushing, occurring primarily from populations in the teat duct, can also contribute to the dissemination of pathogens to mammary glands that will be milked subsequently in the same teatcup. Low environmental temperatures appeared to increase the dissemination.