Abstract
Surveillance programs for mastitis in most tropical countries are not
practiced although that has been an important herd health program in
countries with advanced dairy industries. A cross sectional survey was
carried out in wet and dry periods in three districts of Bangladesh. In each
period, 312 cows from 44 herds in Sirajgonj, 301 cows from 56 herds in
Satkhira and 278 cows from 41 herds in Chittagong were examined to
determine the prevalence and risk factors of mastitis. A total of 209 milk
samples in the wet period and 123 milk samples in the dry period were
collected from cows that were positive to California Mastitis Test (CMT). The
samples were processed to culture individually on Blood and MacConkey
agars at 37°C for 48 hours. The cultured plate was screened and further
biochemical characterization was performed for identification of bacteria and
determination of antimicrobial susceptibility of the isolates (Investigation I).
One hundred pregnant cows (36 cows from 17 herds in Sirajgonj, 32 cows
from 16 herds in Satkhira and 32 cows from 13 herds in Chittagong district)
affected with sub-clinical mastitis were selected for a dry cow therapy; 50
cows received the treatment and other 50 served as control (DCT,
Investigation II). The data were analyzed by binary logistic regression and
paired t-test by using SPSS to determine the associations between risk factors
and mastitis, significance of individual variable and periodic effects on
mastitis in cows. Sub-clinical mastitis was higher (p < 0.05) in herds, cows
and quarters (26.0, 21.0 and 7.8%, respectively) in the wet period than that of
dry period (17.0, 9.0 and 4.4%, respectively). Moderate clinical mastitis was
higher (p < 0.05) in cows and quarters (4.0 and 1.5%, respectively) in dry
period than those in the wet period (1.0, and 0.2%, respectively). Sub-clinical
mastitis was higher (29.0%; p < 0.05) (29.0%) in Chittagong than those in the
Sirajgonj and the Satkhira districts (16.0 and 19.0%, respectively) during the
wet period. Herd size, floor conditions, feeding of cows before or after
milking, age of cows, month in lactation and udder cleanliness were
identified as risk factors that influenced the prevalence of mastitis. Congulase
Negative Staphylococcus (CNS) was identified as the most common cause of
sub-clinical mastitis in cows irrespective of periods while Enterobacter spp.
was identified as the least common cause in the wet period and Klebsiella spp.,
Acinetobacter spp. and Streptococcus agalactiae were identified as the least
common cause of sub-clinical mastitis in the dry period (Investigation I). In
the investigation II, more cows that received DCT recovered from sub-clinical
mastitis (p < 0.05, 78.0%) than did non-treated control cows (38.0%). The
economic benefit of the administration of DCT in individual cow was US$ 33
per six month. Further investigations on developing protocols for the
treatment of mastitis based on milk microbial culture and extension of dry
cow therapy are needed as components of an effective surveillance program
to control bovine mastitis in Bangladesh.