Variation of Edema Scores from Herd-Year, Age, Calving Month, and Sire

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Abstract
Udder edema was scored by herd personnel in 6 Holstein herds in North Carolina [USA]. Scores ranged from 1 (none) to 5 (extremely severe) at calving and at 1 and 2 wk postpartum. Mean scores and SD were 2.91 .+-. 0.71 at calving, 2.12 .+-. 0.71 at 1 wk and 1.54 .+-. 0.64 at 2 wk. Total score, the sum of the 3 ratings for each calving, averaged 6.57 .+-. 1.89. Scores differed by herd-year and lactation but not by month of calving. Heritabilities within 1st, 2nd and grouped later (.gtoreq. 3) lactations were estimated by parental half-sister covariance analyses from 2 subsets of the data. The 1st data set included sires with 5 or more daughters; the 2nd, sires with 10 or more daughters. Heritabilities averaged 0.13 for 1st lactations, 0.10 for 2nd lactations and 0.12 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. Desirability of such progeny tests depends on the relative importance and economic impact of reduced edema severity in the dairy cattle population.