Variation of edema scores from herd-year, age, calving month, and sire

Edema was scored by herd personnel in six Holstein herds in North Carolina. Scores ranged from 1 (none) to 5 (extremely severe) at calving and at 1 and 2 wk postpartum. Mean scores and standard deviations were 2.91 +/- .71 at calving, 2.12 +/- .71 at 1 wk, and 1.54 +/- .64 at 2 wk. Total score, the sum of the three ratings for each calving, averaged 6.57 +/- 1.89. Scores differed by herd-year and lactation but not by month of calving. Heritabilities within first, second, and grouped later (greater than or equal to 3) lactations were estimated by paternal half-sister covariance analyses from two subsets of the data. The first data set included sires with 5 or more daughters; the second, sires with 10 or more daughters. Heritabilities averaged .13 for first lactations, .10 for second lactations, and .12 for later lactations. When adjusted to underlying normal distribution, heritabilities were increased. These heritabilities suggest that progeny tests based on 50 or more daughters should identify bulls transmitting more persistent edema. The desirability of such progeny tests depends on the relative importance and economic impact of reduced edema severity in the dairy cattle population.