Research reported in the July issue of the Journal of Dairy Science offers a glimpse into some of the factors associated with abortions in dairy cattle. The study was conducted by the USDA-Agricultural Research Service Animal Improvement Programs Laboratory and the National Association of Animal Breeders.

It found that the frequency of abortions recorded through Dairy Herd Improvement (DHI) from 2001 through 2009 among lactating cows was 1.31% for 8.5 million lactations. This study did not examine the frequency of early abortions that are typically seen on most dairy farms between the first pregnancy diagnosis (30 to 40 days) and the second confirming diagnosis (60 to 80 days). Many of these early abortions (embryonic deaths; 10 to 15%) are not reflected in the data summary. 

In addition, the analysis found: 

  • Abortions in this sample were most frequent during mid pregnancy: 4.38% for 152 to 175 days postbreeding and 0.59% for 226 to 250 days postbreeding.
  • Frequency was greatest for parity one (1.40%) and lowest for parity eight or higher (1.01%).
  • Recorded abortions were most frequent from May through August and least frequent from October through February.
  • Cows with largest milk yields had more recorded abortions than their lesser-yielding contemporaries.
  • Frequency of DHI-recorded abortions was higher for Holsteins (1.32%) than for Jerseys (1.10%) and other breeds (1.27%).
  • Little relationship was found between DHI-recorded abortions and herd size.

Source: Dairy Cattle Reproduction Council Newsletter, August 2012