A study of mastitis in two small experimental dairy herds managed either organically or
conventionally, over one year
BY K.E. SILVA, A.K. QUINN, P.C.H. MOREL, C.W. HOLMES, A. THATCHER, N.M. SHADBOLT AND T. KELLY COLLEGE OF SCIENCES PRESENTED BY: NATALIE BUTCHER,
AGRICULTURAL SERVICES MASSEY UNIVERSITY
Organic dairying in
New Zealand, and Mastitis
Interest in organic dairy farming systems is growing (about 70 farms certified or in the process of conversion).
Fonterra plans to grow to 200 farms by 2009, and to meet the USDA organic requirements by 2007.
Use of antibiotics is very limited, and will be prohibited after 2007.
Mastitis is a very important topic, about which there is little published information for New
Zealand.
This study; Mid-lactation 2003 to calving 2004
Two farmlets (20 hectares each), at the Dairy Cattle Research Unit, Massey
University.
One farmlet (46 cows) managed organically, (Certified with Agriquality, in 2003), while the other herd (51 cows) managed
conventionally.
Teats were disinfected after every milking.
In the organic herd, homeopathic remedies were used to assist the control of mastitis (persistent clinical cases were given
antibiotics and a prolonged quarantine).
Methods
Single quarter samples were taken
aseptically from every quarter of all cows at four sample times.
These were: Mid lactation, 2003; before Dry-off, 2004; after calving and 14 days later, 2004.
These samples were subjected to
bacteriological analyses, using standard methods.
Analysis of Results
Bacterial growth data was subjected to an analysis of variance within each sample time.
Somatic cell counts, from monthly herd tests, were subjected to a
repeated measurements analysis of
variation, after a natural logarithmic
transformation.
Results
The differences were significant only for Staphylococcus aureus.
The organic herd generally had slightly higher bacterial growth and somatic cell counts, but these differences were not significant.
Average yields of milk solids per cow (from herd tests) in each herd were 412kg and 430kg in the organic and conventional
herds respectively.
Percentages of quarters in each herd at each sample time, with positive growth of
Staphylococcus aureus.
Significance of difference between the herds
0 4 8 12
Mid- lactation 2003
Dry off Calving 2004 Calving + 14 days
Percentage of quarters
P<0.01 P<0.05 P<0.01 P<0.01
Organic
Conventional
0 4 8 12
Mid- lactation 2003
Dry off Calving 2004 Calving + 14 days
Percentage of quarters
P<0.01 P<0.05 P<0.01 P<0.01
Organic
Conventional
Percentages of quarters in each herd at each sample time, with positive growth for Streptococcus uberis
(No significant differences between herds)
0 2 4 6 8 10
Mid lactation 2003
dry off 2004 Calving 2004 Calving + 14 days
Percentage of Quarters
Organic
Conventional
0 20 40 60 80 100
Mid Lactation 2003
Dry Off 2004
Calving 2004
Calving + 14 days
Percentage of Quarters
Percentages of quarters in each herd at each sample time, with (a) No bacterial growth or
(b) No growth plus coagulase negative Staphylococcus
(a) (b)
Conventional Organic
Percentages of cows with SCC either : (a) below 200 or (b) above 400 (thousand cells/ml)
The overall mean values for each herd were:
Organic: logn=4.75 (116,000) Conventional: logn=4.62 (102,000)
0 20 40 60 80 100
aug sep oct nov dec jan feb mar apr
Percentage of cows
organic
conventional (a)
(b)
Discussion and Conclusion
The pattern of infections by
Staphylococcus aureus and Streptococcus uberis are generally similar to recent data from conventional herds in New Zealand.
The incidences of clinical mastitis were higher than recent data for conventional herds in New Zealand, but similar to
reports in organic and conventional herds in England.
Discussion and Conclusion cont
The organic herd recorded higher somatic cell counts than the conventional.
Cows with high SCC were usually infected with Staphylococcus aureus.
The present study, although small and short, highlights the potential importance of
Staphylococcus infections in organic herds.
Effective prevention of this organism in organic herds will be essential, because treatment will be impossible without
antibiotics.
Acknowledgements
The following are gratefully acknowledged:
Dairy Insight for funding towards the trial.
Staff in the Microbiology Laboratory, IVABS, for helping the first author, and staff at the Dairy Cattle Research Unit.
The NZ government, for a scholarship to the first author.
