R.H. Miller1, M.T. Kuhn, H.D. Norman, and J.R. Wright
Animal Improvement Programs Laboratory, Agricultural Research Service, USDA, Beltsville, MD 20705-2350
2007 J. Dairy Sci. (?)
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Factors that affect frequency of death of lactating cows were studied for cows with records that terminated from 1995 through 2005. Analyses included effects of herd, year, month, parity, and lactation stage at lactation termination as well as cow breed and milk yield. A sample of 1,645 herds was used to compare 2 analysis methods (PROC GENMOD and PROC GLM). Because the 2 methods ranked effects similarly, national data (15,025,035 lactations in 45,032 herds) were analyzed with PROC GLM. Overall death frequency was 3.1% per lactation (5.7% per cow). Death frequency increased by 1.6% from 1995 to 2005, with a sudden increase of 0.9% from 2003 to 2004, probably because of a USDA requirement in late 2003 for euthanizing downer cows. Death frequency was 16.5% higher for lactations that terminated at <46 d than for those that terminated at >250 d. Death frequency increased with parity (2% higher for eighth parity and later than for first parity). Deaths were most frequent in July and least frequent in November. Within-herd breed differences (Holstein, Jersey, and other breeds) were small. Death frequency increased as lactation milk yield increased. The heritability of likelihood of death estimated from a sample of 79,162 Holstein cows was 1.3%.
(Key words: death loss, death frequency, lactation termination)