Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: February 27, 2007
Publication Date: July 8, 2007
Citation: Miller, R.H., Norman, H.D., Kuhn, M.T., Wright, J.R. 2007. Factors affecting death rate of lactating cows in Dairy Herd Improvement herds. Journal of Dairy Science. 90(Suppl. 1):11(abstr. M24). Technical Abstract: Frequencies of deaths of lactating cows of all breeds during 2001 to 2005 were estimated from an approximate 10% sample of national DHI herds (based on units position of herd code). Herds with <400 lactations across years were excluded. Because the trait is binomially distributed, PROC GENMOD of SAS was used (0=live, 1=dead). To prevent failure to converge, herds with < 0.3% frequency of deaths were excluded. The model included herd, year lactation ended, month lactation ended, and parity (1, 2, …, >=8). After the above exclusions, 998,599 lactations (793 herds) were analyzed. Actual frequency of deaths was 3.9%. All effects were significant (P < .0001). Chi-square values for herd, year, month and parity were 14,826, 1447, 209, and 6990, respectively. GENMOD parameter estimates were converted to a least-squares means expression on the binomial scale. Differences among months were small, but frequencies were slightly higher in February and March. Estimates of parity differences relative to first parity (%) were 0.8, 2.1, 3.1, 3.8, 4.3, 4.5, and 5.8 for parities 2 to >=8, respectively. Death rates steadily increased with parity. Cows in >=8th were 4 times more likely to die than those in first parity. Estimates of year differences relative to 2001 (%) were 0.1, 0.5, 1.9, and 2.1 for 2002 to 2005, respectively. Death rates increased from 2001 to 2005. However, the sharp increase in frequency from 2003 to 2004 may have been due to changes in regulations for disposal of downer cows.