The contribution of each effect to the total sum of squares was herd (2.6%);year of first calving (2.83%);month of calving (1.93%);parity (4.18%);age (14.87%), and individual animal effect (46.72%).

• 各因子的方差占总方差的比例分别为：畜群（2.；6%25）、头胎年份（2