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Animal Improvement Programs Laboratory, Agricultural Research Service, USDA, Beltsville, MD 20705-2350
1 Corresponding author: millerrh{at}juno.com
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 national data set (15,025,035
lactations in 45,032 herds) was 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%
greater for lactations that terminated at 
45 d than for those that
terminated at 
251 d. Death
frequency increased with parity (2% greater for eighth parity and
later than for first parity) and with lactation milk yield
(0.4%/1,000 kg for Holsteins and Jerseys and 0.5%/1,000 kg for other
breeds). Deaths were most frequent in July and least frequent in
November. Within-herd breed differences (Holstein, Jersey, and other
breeds) were small. The heritability of likelihood of death estimated
from a sample of 79,162 Holstein cows was 1.3%. Death losses are
increasing, perhaps partly because of increased milk yield and
more intensive management regimens.
Key Words: death loss • death frequency • lactation termination
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