Factors affecting death rate of lactating cows in Dairy Herd Improvement herds R. H. Miller, H. Duane Norman, M. T. Kuhn* and J. R. Wright Animal Improvement Programs Laboratory, Agricultural Research Service, USDA, Beltsville, MD Abstract M CONCLUSIONS Frequency of deaths of lactating cows increased by 1.7% from 1995 to There was a sudden increase of 0.7% from 2003 to 2004, probably due to the December 31, 2003 change in USDA regulations for euthanizing downer cows because of BSE concerns. Estimates of deaths do not include lactations ending prior to first test which were only reported by DRPC in recent years Death was more likely to occur in early lactation than later. Compared to lactations longer than 250 d, lactations that terminated at less than 46 d had a 16.5% higher death rate. Death rate steadily increased with parity. By the 8 th or greater parity, death rate was 2.01% higher than for first parity cows. Differences among calendar months were relatively small. Frequencies were highest in July, lowest in November (difference of 0.55%). Within-herd breed differences were very small. Frequency of death increased as 305-ME milk yield increased. REFERENCES 1 RESULTS & DISCUSSION Table 1. Analysis of variance results for both PROC GENMOD and PROC GLM of SAS Figure 1. Least-squares estimates (LS) of model effects a)Year trends compared to Death losses were most frequent in latest year (2005), lowest in There was a large increase from 2003 to 2004 (0.7%). The total increase from 1995 to 2005 was 1.72%. The large increase from 2003 to 2004 was likely due primarily to a change in USDA regulations to require that “downer” cows be euthanized 1. While the frequency of downer cows euthanized prior to 2004 is unknown, the 0.7% increase observed indicates a substantial new economic loss for dairymen. b)Parity trends compared to 8+ parities. As anticipated, frequency of death steadily increased from first to subsequent parities. Death rate in first parity was 2.01% lower than in 8+ parities. c)Month trends compared to December. Although differences are significant among calendar months, magnitudes were small. Deaths were least frequent in November, most frequent in July (0.39% higher than December). Trend was for peak in July through August, declining to November, then rising steadily through winter and spring. Whereas estimated differences generally closely paralleled actual frequencies, month trend was an exception, where records ending in February had the highest actual death rate (3.21%). Herd effects may have been responsible for this discrepancy. d)Stage of lactation differences compared to > 250 d. As expected, deaths were much more frequent during early lactation (short records would be represented by deaths and voluntary disposals). Compared to lactations that were longer than 250 d, death rate in lactations < 46 d was 16.5% higher and death rate in lactations of 46 to 90 d was 9.8% higher. INTRODUCTION There are anecdotal reports of increased deaths of lactating cows. OBJECTIVES Assess death losses of lactating cows Determine effects of year, season, parity, stage of lactation at death, breed, and lactation milk yield on frequency of death among lactations MATERIALS & METHODS Lactations ending during 1995 through 2005 were extracted for a 10% sample of herds based on units position of herd code. The following records were excluded: 1) Lactations ending less than 1 year prior to herd leaving test; 2) Lactations without estimates for 305-ME milk yield. Death incidence was binomial (0=live, 1=died) based on termination code 6 reports by DRPC. PROC GENMOD of SAS was employed for a binomial distribution. To insure convergence, herds with less than 400 lactations and herds reporting less than 0.3% deaths were excluded (to guard against incomplete reporting). Remaining for analysis were 2,131,035 lactations from 1,646 herds. Observed frequency of death was 2.92%. The model included herd, year, and month in which lactation ended, parity (8 groups), DIM stage of lactation, breed of cow, and 305-ME milk yield. DIM stage of lactation was defined as 250 d. To compare breeds within herd, 3 groups were Holstein, Jersey, and Other. Because the sample was large, the model was also fit with PROC GLM of SAS. YearMonthParityStageBreed Chi-Square (GENMOD)1, , , F-values (GLM) , RESULTS (con’t.) Within-herd breed differences were small. Differences from other breeds were 0.45% for Holstein and 0.50% for Jersey. Regressions on lactation milk yield (%/1000 lb) were 0.15 for Holstein, 0.19 for Jersey, and 0.22 for other breeds (t-values were > 10). GENMOD and GLM ranked the model effects similarly: stage, parity, year, month, and breed (largest to smallest). Stage was by far the most dominant effect, especially for GLM. All effects were significant, but breed differences were negligible. Because GENMOD and GLM ranked effects similarly, only GLM estimates are presented.