Observations on intramammary infections in first calf heifers in early lactation

Intramammary infections and mastitis were monitored on four occasions at three-week intervals in 61 first calf heifers in five dairy herds during the first ten weeks of lactation. Of 940 quarter milk samples examined 65% were classed as negative, 10.4% as positive for mastitis (mainly subclinical), 1.8% as group 3 (infection present but no elevation in somatic cell count) and 22.8% as group 4 (elevated somatic cell count). Seventy-seven percent of the infections detected and identified were those due to coagulase-negative staphylococci, the main species being S. hyicus, S. epidermidis, S. simulans and S. hominis. Other infections detected with Corynebacterium pyogenes (three samples), Escherichia coli (one sample), Micrococcus spp. (one sample), S. aureus (two samples) and Streptococci (non-agalactiae) (seven samples).The geometric mean somatic cell count for 23 quarters infected with coagulase-negative staphylococci was 311 x 10(3) cells / mL compared to 134 x 10(3) cells / mL in noninfected adjacent contralateral quarters. The respective figures for% cell volume in Channel 8 (mainly neutrophils) were 10.6% and 3.5%. There was a highly significant association between herd and the proportion of quarter milk samples in the four mastitis categories.