Comparison of milk somatic cell counts by Coulter and Fossomatic Counters

Unpreserved milk samples from 28 quarters of 18 cows were used to compare milk somatic cell counts obtained by Fossomatic and Coulter Counter and to determine effect of temperature and sample age on Fossomatic counts. Samples represented high and low cell count milk (16 cows) and colostrum (2 cows). Fifteen milliliters of both foremilk (after milking preparation) and strippings were obtained; one-third was used for Coulter and two-thirds for Fossomatic. Milk for Fossomatic was subdivided once for fresh and 24-h determinations and once again for heating to 40 and 60 degrees C for 15 min. Analysis of log10 count included effects for quarter, Fossomatic versus Coulter, and (for Fossomatic) sample age, incubation temperature, and age-temperature interaction. For foremilk, geometric means of Coulter milk somatic cell counts and Fossomatic counts were not different. For Fossomatic, milk samples incubated at 60 degrees C counted higher than those at 40 degrees C (230,096 versus 173,638); 24-h samples counted higher than fresh (201,679 versus 192,380). For strippings, Coulter counted higher than Fossomatic (700,521 versus 570,033). Interaction of time and temperature was significant for Fossomatic. Counts from samples held 24 h and heated to 60 degrees C were highest (553,291). Fossomatic counts from fresh samples at 40 degrees C were lowest (447,729). Geometric means of original milk samples from 14 of the quarters obtained by direct microscopic, Fossomatic, and Coulter counts were 199,300, 311,000, and 399,300, respectively.