Jh. Williamson et al., THE PROPHYLACTIC EFFECT OF A DRY-COW ANTIBIOTIC AGAINST STREPTOCOCCUS-UBERIS, New Zealand Veterinary Journal, 43(6), 1995, pp. 228-234
The prophylactic use of a dry-cow antibiotic for reducing the incidenc
e of mastitis due to Streptococcus uberis was studied in four seasonal
ly calving dairy herds involving 378 cows. The treatment was a long-ac
ting dry-cow antibiotic preparation administered immediately after the
last milking of lactation. New intramammary infections were identifie
d by comparing the bacteriological status of quarters at drying off wi
th that after calving, or through manual udder palpation during the dr
y period. The administration of dry-cow antibiotic to uninfected quart
ers at drying off reduced the overall incidence of new infections with
Streptococcus uberis from 12.3% for untreated quarters to 1.2% of qua
rters (p < 0.01). The reduction was significant (p < 0.01) for both dr
y-period and post-calving infections. The susceptibility of uninfected
quarters to new infection by Streptococcus uberis appeared to be unre
lated to the infection status of a cow at drying off. Clinical infecti
ons during the dry period were most prevalent (97%) in quarters identi
fied as having open teat canals. Fewer open teat canals (p < 0.05) wer
e observed among antibiotic treated quarters over the first 4 weeks of
the dry period. Treated quarters had a lower (p < 0.05) incidence of
new clinical infection during the ensuing lactation and lower somatic
cell counts. This did not affect production levels of milk, milk fat o
r protein. The results clearly indicated a prophylactic benefit for th
e dry cow antibiotic treatment against new Streptococcus uberis infect
ions during the dry period.