Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: February 25, 2008
Publication Date: July 11, 2008
Citation: Miller, R.H., Kuhn, M.T., Norman, H.D., Wright, J.R. 2008. Factors affecting abortion frequency in dairy herd improvement herds in the United States. Journal of Dairy Science. 91(E-Suppl. 1):8(abstr. T21). Technical Abstract: Frequency of abortions among lactating cows during 1995-2005 was studied. Only lactations with breeding dates were used. Abortion frequency was 1.51% among 2,980,527 lactations (>151d pregnant by end of lactation). Observed frequency of abortion was 1.6% in 2005. Analyses were conducted to determine effects of herd, year, month, and stage of pregnancy at end of lactation, breed (Holstein, Jersey, Other), and milk yield. Supplemental analyses examined effects of herd size and geographical region. A preliminary analysis of a sample of 483 herds compared the results of PROC GENMOD and PROC GLM. Results were similar and the national data set was analyzed using GLM. Abortions were most frequent in July, least in December (difference of 0.38%). Frequency of abortion decreased from 1st to > 7th parity (difference of 0.52%). There was a non-linear trend in frequency of abortion with stage of gestation. Compared to >241d, frequency at 152-181d was 3.14% higher but frequency at 212-241d was 1.07% lower. Compared to Other breeds, Holsteins aborted 0.38% more frequently; frequency in Jerseys was only 0.07% higher than Other. Regressions on lactation milk yield were 0.26%, 0.26%, and 0.19% per 1000kg for Holsteins, Jerseys, and Other, respectively. The regressions primarily accounted for the differences among breeds. Frequency of abortion was 0.95% higher in herds with 700-799 lactations than in herds with 50-99 lactations. California herds had highest abortion frequency (2.18% higher than the state with lowest frequency (North Dakota)). Abortions were most frequent during 152 to 182 d of pregnancy.