Selective dry cow therapy in New Zealand
Selective dry cow therapy (DCT) has always been promoted as best practise in New Zealand. However, a combination of farmer concerns, milk processors focus on reducing bulk milk somatic cell count (BMSCC), and rare clinical mastitis cases following infusion of internal teat sealants, has resulted in only about half the farms in New Zealand currently implementing selective dry cow therapy.
In response to these concerns, a retrospective analysis of BMSCC and on-farm antimicrobial use for clinical mastitis therapy was recently undertaken. The study of approximately 280 dairy farms (~ 1,100 herd years) over a period of up to 8 seasonal lactations demonstrated that there was no difference in clinical mastitis antimicrobial use between herds using selective compared with blanket DCT. Overall there was little difference in BMSCC between herds undertaking blanket compared with selective DCT. However, there was a lower BMSCC in blanket compared with selective DCT herds amongst that subset of herds where the lactational BMSCC was greater than 250,000 cells/mL and where late lactation increases in BMSCC were greater than 50,000 cells/mL. Analysis of data from farms over multiple years demonstrated that farms were able to maintain BMSCC at acceptable levels for up to 8 years after implementation of selective DCT. Conversely, ongoing use of blanket DCT was not associated with continuing declines in BMSCC. So while antimicrobial DCT is an important tool to manage infection, it is clear that other mastitis control strategies must be implemented in conjunction with antimicrobial DCT to manage milk quality.
Following this research, an updated technical note has been provided to veterinarians and rural advisors (scan QR).
Additionally an extensive national roadshow was undertaken by DairyNZ (the farmer funded industry body), the Veterinary Council of New Zealand (the veterinary profession’s governing body ), the Dairy Cattle Veterinarians of the New Zealand Veterinary Association, and Cognosco.
McDougall is a veterinarian with nearly 40 years of experience in clinical practice, academia, research and extension. He has postgraduate training in production medicine, and a PhD in cattle reproduction. He is a registered specialist in cattle reproduction and an adjunct Professor at the School of Veterinary Science at Massey University. He has published extensively on epidemiology, treatment and control of mastitis. He is a member of the New Zealand National Milk Quality Advisory Committee and has been involved in development and extension of New Zealand mastitis control programme (SmartSAMM). He is a member of the Ministry for Primary Industries Endemic Disease Forum. Scott has consulted and/or taught about mastitis around the world.
