Genetics statistics and relationships of teat and udder traits, somatic cell counts, and milk production

Teat lengths and diameters, udder clearance, cleft depth, and distances between teats were measured from 1967 to 1982 on Holstein cows. Numbers of observations per trait ranged from 5934 to 11,449. Cows were from six herds owned by the North Carolina Department of Agriculture and two research herds of North Carolina State University. Repeatabilities between adjacent lactations for physical traits of udder were mostly between .60 and .80. Repeatabilities between first and second lactations for average somatic cell count and mean log somatic cell count were .11 +/- .04 and .21 +/- .04. Heritabilities in first lactation were .63 for front teat length, .44 for teat diameter, .56 for rear udder clearance, .10 for cleft depth, .32 for mature equivalent milk, and .18 for somatic cell counts. Heritabilities of distances between teats ranged from .33 to .48. Cows with udder clearance higher from the ground, deeper clefts, smaller distances between teats, and teats of smaller diameter had lower somatic cell counts. Multiple regression analysis showed that dams' somatic cell counts and rear udder clearances were not significant predictors of daughters' somatic cell counts. Lactation average somatic cell counts of daughters were predicted with greater accuracy from averages of somatic cell counts of multiple lactations of dams than from single lactations of dams. Milk production and somatic cell counts seemed positively genetically correlated, more so in first than later lactations.