Abstract
Staphylococcus aureus and Streptococcus agalactiae are important contagious mastitis pathogens and are considered to mainly transmit between cows through the milking machine. Controlling contagious mastitis on dairy farms requires a reduction of the transmission rate or the duration of intramammary infections (IMI), or both. These parameters may differ in dairy herds milked with an automatic milking system (AMS) as compared to those milked with a conventional milking system (CMS). The aims of this prospective longitudinal study were to estimate the transmission rate, the median duration of IMI and the basic reproduction number (R0) of Staph. aureus and Strep. agalactiae in a Dutch AMS herd. Bacteriological cultures of quarter milk samples were collected every 2 wks. Using 3 different definitions of IMI, we estimated the transmission rate for Staph. aureus to be within the range of 0.002 (95 % CI: 0−0.005) quarter-day−1 to 0.019 (95 % CI: 0.010−0.032) quarter-day−1, and for Strep. agalactiae of 0.007 (95 % CI: 0.005−0.010) quarter-day−1 to 0.019 (95 % CI: 0.011−0.032) quarter-day−1, the median duration of chronic IMI at 95 (95 % CI: 72−125) days for Staph. aureus and at 86 (95 % CI: 67−111) days for Strep. agalactiae, and the R0 between 0.16 (95 % CI: 0.05−0.27) and 0.34 (95 % CI: 0.20−0.48) for Staph. aureus, and between 0.64 (95 % CI: 0.41−0.87) and 0.68 (95 % CI: 0.48−0.88) for Strep. agalactiae.Transmission of these two contagious pathogens in this herd was limited and theoretically the IMI would not sustain, given that R0 of both pathogens was lower than 1. The estimated transmission rate of Staph. aureus in this AMS herd was found to be comparable to those described for CMS herds, while for Strep. agalactiae, it was slightly higher than in CMS herds. The duration of Staph. aureus IMI was in line with results from CMS farms, while the duration of Strep. agalactiae was lower than what has been described in CMS herds. The R0 of these contagious pathogens was found to be lower than the estimates in CMS herds. Our study suggests that the transmission rate of these two contagious pathogens in this AMS herd were comparable to what has been reported about well-performing CMS herds that have a low rate of transmission.
Highlights
Contagious mastitis pathogens have long been the subject of research, and the five-point mastitis control plan has been shown to significantly reduce their prevalence (Green and Bradley, 2013), there still is much to gain in this respect in many farms worldwide (Bradley et al, 2015; Gao et al, 2017; Leuenberger et al, 2019)
Controlling contagious mastitis on dairy farms requires a reduction of the transmission rate or the duration of intramammary infections (IMI), or both
These parameters may differ in dairy herds milked with an automatic milking system (AMS) as compared to those milked with a conventional milking system (CMS)
Summary
Contagious mastitis pathogens have long been the subject of research, and the five-point mastitis control plan has been shown to significantly reduce their prevalence (Green and Bradley, 2013), there still is much to gain in this respect in many farms worldwide (Bradley et al, 2015; Gao et al, 2017; Leuenberger et al, 2019). Recent research found its prevalence to be relatively high in herds using an automatic milking system (AMS) (Svennesen et al, 2019) and proved the existence of an environmental transmission route of Strep. Transmission rates of these pathogens have been estimated in herds using conventional milking systems (CMS)
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