SOMATIC-CELL COUNTS - ASSOCIATED FACTORS AND RELATIONSHIP TO PRODUCTION

  • 1 January 1984
    • journal article
    • research article
    • Vol. 48  (3) , 251-257
Abstract
Factors affecting somatic cell counts and the association between somatic cell counts and milk production were evaluated. Data were collected from 748 Ontario Dairy Herd Improvement Corporation supervised herds that were on production and somatic cell count programs between April 1981 and March 1983. Two data files were created; one, the lactation summary file, contained 1 record/cow on each of 9406 Holsteins and the other, the test day file, included results of all tests during the complete lactation on each of the above cows. The latter file contained 85,236 records. Multiple curvilinear least squares regression was used to create 5 separate models. The dependent variables used in the models were natural logarithms (Loge) of the geometric mean of the somatic cell count for the lactation, 305 day milk production and breed class average for milk from the lactation summary file, and loge of the 24 h somatic cell count and 24 h milk production from the test day file. The somatic cell count at both the lactation and test day level increased with age up to .apprx. 10 yr and thereafter slowly decreased. The variable days in milk was not significantly associated with the lactation average somatic cell count. A curvilinear relationship was found between days in lactation at the time of test and the somatic cell count of 24 h milk production. The somatic cell count increased until .apprx. 250 days in lactation and thereafter slowly decreased. The highest cell counts occurred in summer and the lowest in winter. One unit increase in the loge of the geometric mean of the somatic cell count was associated with a loss of .apprx. 4 breed class average units and 247 kg of 305 day milk production. One unit increase in the loge of the 24 h somatic cell count was associated with a decrease of 0.65 kg of test day milk production.