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Factors that affect abortion frequency in dairy herds in the United StatesR.H. Miller,* M.T. Kuhn, H.D. Norman, J.R. Wright
Animal Improvement Programs Laboratory, Agricultural Research Service, USDA, Beltsville, MD 20705-2350
Abstr. T21
INTRODUCTION
Abortions cause significant economic losses of $500 to $900 per occurrence.
Reports indicate herd abortion frequencies of 3 to 5% per year (Hovingh, 2002).
OBJECTIVES
Determine the incidence of lactations ending in abortion in the United States.
Estimate differences in abortion frequency by parity, season, stage of pregnancy, and breed.
Determine association of abortion frequency with milk yield, geographic location, and herd size.
DATA & METHODS (cont.) Analysis model:
Abortion frequency =herd-year (absorbed)
+ month of abortion (Jan., Feb., etc.)+ parity (1,2,…7, ≥8)+ breed (Holstein, Jersey, all others)+ pregnancy stage (152-181d, 182-211d,
212-241d, ≥242d) + milk production level within breed
(lowest 20%, middle 60%, highest 20%)
Supplemental analysis of herd-year means was conducted to determine effects of geographic location of herd (state) and herd size (50-99, 100- 199, 200-299… ≥1000)
Likelihood of abortion declines with advancing parity, (decrease of 0.57% from 1st to ≥ 8th).
CONCLUSIONS
Spring and summer may favor the spread of infectious agents causing abortion.
Younger cows have higher rates of abortion perhaps due to less acquired immunity to infectious agents.
Frequency of abortion increases as herd size or milk yield increases.
The relationship between stage of pregnancy and abortion rate does not appear to be linear.
Breed differences were small but significant (p<.01). (Holsteins 0.25% higher than Jersey and other breeds).
Geographic location differences were 2.2% more extreme from highest (California) to lowest (North Dakota).
DATA & METHODS
Lactation records from USDA national dairy database edited for:
Terminated during 1995-2005 Had breeding dates reported Terminated > 1 year prior to herd’s last
test Had milk yield reported
Abortion record definition:
Coded with Dairy Herd Information (DHI) termination code of ‘8’
Had days pregnant ≥ 152
Preliminary analysis:
Used only herds with >499 lactations (483 herds; 759,394 lactations)
Compared GENMOD versus GLM. Results were similar, so GLM was chosen for entire data set.
Entire data set contained 28,272 herds; 2,980,527 lactations.
RESULTS (cont.)
The range between highest (July) and lowest (December) was 0.34%.
Effects seem to be seasonable; February-August (high) and September-January (low).
RESULTS (cont.)
Observed abortion frequencies
Month Frequency (%) Parity Frequency (%) January 1.40 11.58 February 1.66 21.51 March 1.75 31.51 April 1.64 4 1.44 May 1.58 51.39 June 1.55 6 1.32 July 1.53 71.35 August 1.52 ≥81.27 September 1.49 October 1.46 Days Pregnant November 1.39 152-181 4.77 December 1.32 182-211 2.57
212-241 0.88≥242 1.29
http://aipl.arsusda.gov/
RESULTS
Least square estimates
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
Herd size
2008
Stage of pregnancy differences
Days pregnant 152-181 182-211 212-241 ≥242LS estimate 3.23 0.90 -1.10 0.00
Milk level differences by breed
Breed High Medium Low
Holstein 1.37 0.75 0.0
Jersey 1.15 0.69 0.0
Other 0.93 0.55 0.0
Abortion rate was highest at 152-181 days of pregnancy.
Higher production per cow was associated with higher abortion rates in all breeds.
0
0.1
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0.4
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Month of abortion
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Season differences
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0.1
0.2
0.3
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1 2 3 4 5 6 7 8+Parity
Overall frequency of abortion was 1.51%. Monthly abortion means ranged from 1.32%
(December) to 1.75% (March).
Mean by parity for abortion ranged from 1.27% (≥ 8th parity) to 1.58% (1st parity).
Mean abortion rate was highest (4.77%) in earliest stages of pregnancy and lowest in 212-241 days pregnant (0.88%).
Parity differences
Fre
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Herd size differences
Abortion frequency increased nearly 1% from the smallest herds to 700-799 herd size.
Fre
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