Management of dairy heifers and its relationships with the incidence of clinical mastitis.
OBJECTIVE
To describe aspects of management of dairy heifers before calving and determine risk factors for clinical mastitis postpartum in heifers, at the herd level, under pasture-based management systems in the Waikato and Taranaki regions of New Zealand.


METHODS
Dairy herdowners (n=578) provided information via a prospective survey about their practices for rearing heifers and management of mastitis. A proportion of herdowners (n=250) subsequently provided data on the cases of clinical mastitis in their herds, including the date, cow identification, age and quarter affected from cases occurring in the 4 months after the planned start of calving (PSC) in the subsequent lactation. The relationship between management factors and the proportion of heifers diagnosed with clinical mastitis within a herd was examined using bivariate and multivariate analyses.


RESULTS
The herd average percentage of heifers with clinical mastitis was 13.6 (95% confidence interval (CI)=12.3-14.9)%, and multiparous cows with clinical mastitis was 9.0 (95% CI=8.2-9.8)% in the first 4 months of lactation. There were positive relationships between the proportion of heifers with clinical mastitis and average milk production per cow (kg milksolids/ lactation; p<0.001), number of cows milked per labour unit (p=0.003), stocking rate (<> 3.30 cows/ha; p=0.002), and incidence of clinical mastitis in multiparous cows (%/120 days; p<0.04), in the final multivariate model. The proportion of heifers with clinical mastitis per herd was lower in herds that milked their lactating cows in multiple groups (p=0.02).


CONCLUSIONS
The risk of clinical mastitis in heifers was significantly associated with management practices. It may be possible to reduce the incidence of clinical mastitis in heifers by modification of management practices at the herd level, and further studies are required to investigate this.
Parker
K I
KI
Animal Health Centre, PO Box 21, Morrinsville, New Zealand. kparker@ahc.co.nz
Compton
C W R
CW
Anniss
F M
FM
Weir
A M
AM
McDougal
S
S
D000822:Animal Husbandry; D000818:Animals; D002417:Cattle; D003612:Dairying; D005260:Female; D015994:Incidence; D008414:Mastitis, Bovine / Q000453:epidemiology* / Q000209:etiology / Q000517:prevention & control*; D009520:New Zealand / Q000453:epidemiology; D011446:Prospective Studies; D012307:Risk Factors; D011795:Surveys and Questionnaires