The investigation was led from February-November 2014 longitudinally to recognize aerobic bacterial isolates, estimate incidence rate, identify the associated risk factors and antimicrobial sensitivity patterns of heifer and cow mastitis in and around Debre-Libanos district. An aggregate of 31 Jersey and Holstein-Fresian cross heifers that were left for less than a month to calve were sampled and pursued for the initial two lactation stages after calving. Clinical heifer mastitis was distinguished by physical examination of the udder and milk while sub-clinical one was recognized by California mastitis test. The incidence rate of heifer mastitis per gland month at risk was observed to be 37.4%. The event of new contamination in heifers and cows was not altogether influenced by gland position and udder cleanliness (P>0.05), yet by the management system, lactation stage and dry cow therapy (P<0.01). From 231 isolates, Staphylococcus aureus (25.1%) was the most prevalent pathogen pursued by coagulase negative Staphylococcus and Streptococcus species (each 14.7%). Other bacterial isolates included Micrococcus species (10.38%), Klebsiela pneumoniea (9.95%), Esherishia coli (12.98%), Corynebacterium species (5.62%), Enterobacter aerogens (4.32%) and Bacillus species (4.32%). Antimicrobial sensitivity test demonstrated that tetracycline (71.7%) was observed to be increasingly successful antibiotic among the whole tried antibiotics against all bacterial isolates while the least effective antibiotic was observed to be penicillin G (24.2%). The present investigation has demonstrated that heifer and cow mastitis specifically; sub-clinical mastitis is a critical sickness affecting heifers' milk production.
Key words: heifer mastitis, incidence rate, risk factors, Ethiopia, antimicrobial sensitivity test
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