A comparison of somatic cell count trends following the treatment of clinical mastitis with and without intramammary antibiotics : a case study on a large, commercial NY dairy

Abstract

Milk cultures from 153 cases of clinical mastitis were taken from day 0 (day at which mastitis case was identified) to 28 days after case identification from cows housed in a commercial, free-stall dairy in New York (Sunny Side Dairy). Cases included in this study were identified by farm personnel as having clinical mastitis based on visible signs (udder and milk quality) and were confirmed using the California Mastitis Test (CMT). Cows were randomly assigned to either a treatment group receiving intramammary (IMM) amoxicillin or a no treatment group. Milk samples were taken from the affected quarter at day 0 for microbiological culture and somatic cell counts (SCC). Additional milk samples were obtained twice weekly for SCC for up to 28 days following the original date of clinical mastitis identification. All cases had a minimum of three milk samples taken. Four pathogen groups were assembled based on culture results: Escherichia coli, Streptococcus spp., No growth and Other (mixed cultures, other common mastitis pathogens). Each pathogen group was then analyzed to determine if there was significant difference in the drop in SCC per day after the identification of clinical mastitis. The results of the study found no significant difference in the rate of decline of SCC post treatment when compared to the rate of decline in SCC for cows receiving no treatment over all pathogen groups. For the Escherichia coli group the SCC dropped numerically more quickly (-0.61) when there was no treatment, but there was no significance difference in the rate of decline of SCC of the two treatment groups (p=0.77). The No growth pathogen group had similar results with a greater rate of decline in SCC (-0.73) when cases did not receive treatment numerically, but no significant difference (p=0.15) between IMM amoxicillin and no therapy. Clinical cases caused by Streptococcus spp. had a slower rate of SCC decline (+1.10) if they did not receive therapy showing a positive numerical effect in SCC decline when IMM amoxicillin was used. This difference, however, was statistically insignificant (p=0.09). The Other pathogen group also showed a numeric benefit in drop in SCC (+0.13) when IMM therapy was used, but as all other groups was not significant (p=0.11). (Key words: mastitis, somatic cell count, intramammary antibiotic therapy)