Globally, herd size continues to increase due to various factors: the removal of the quota system in Europe, the expansion of Chinese dairy production, primarily through an increase in larger herds, and the expansion of the large herd segment, predominant in new investments in Oceania, South America and Northern Japan. Large herds have been particular to some parts of the USA such as California, Texas, Florida and Idaho. Today a major portion of all cows in the USA is milked in larger herds. Increased herd size is normally associated with increased stocking densities and the potential for increased infection pressure. A review of the practices currently employed on larger farms in the USA to maintain milk quality, low infections rates, and low SCC was presented at the 2016 New Zealand Milk Quality Conference (Lopez Benavides et al)*.
Mastitis prevention practices remain driven by the type of organism exerting the most influence on mastitis and milk quality. While contagious pathogens such as S. agalactiae have been practically eradicated, other contagious pathogens, such as S. aureus, remain common causes of sub-clinical mastitis. Environmental pathogen control is increasingly important and these organisms have a strong influence on the optimization of mastitis control practices. The pathogens commonly identified on large dairies include:
S. aureus (66%), E. coil/Klebsiella/other Gram negative (71%). On large dairies the most common pathogen identified from clinical mastitis cases include: E. coli, Klebsiella, environmental streptococci and CNS. This high prevalence of environmental pathogens is the reason 51% of the large operations vaccinate against E.coli.
In spite of the higher stocking densities and assumed higher infection pressure, in the
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