1. Factors that affect abortion frequency in dairy herds in the United States R.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 1 st to ≥ 8 th ). 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 MonthFrequency (%)ParityFrequency (%) January1.40 11.58 February1.66 21.51 March1.75 31.51 April1.64 41.44 May1.58 51.39 June1.55 61.32 July1.53 71.35 August1.52 ≥81.27 September 1.49 October1.46Days Pregnant November1.39152-1814.77 December1.32182-2112.57 212-2410.88 ≥2421.29 http://aipl.arsusda.gov/ RESULTS Least square estimates 2008 Stage of pregnancy differences Days pregnant152-181182-211212-241≥242 LS estimate 3.23 0.90 -1.10 0.00 Milk level differences by breed BreedHigh MediumLow Holstein1.370.750.0 Jersey1.150.690.0 Other0.930.550.0  Abortion rate was highest at 152-181 days of pregnancy.  Higher production per cow was associated with higher abortion rates in all breeds. Frequency difference (%) Season differences  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 Frequency difference (%) Herd size differences  Abortion frequency increased nearly 1% from the smallest herds to 700-799 herd size. Frequency difference (%)