Dynamics of the probability of survival of cows in dairy herds in the United States.

Cow longevity directly affects the economic efficiency of dairy herds, as modern systems exhibit low survival and involuntary losses that compromise genetic and financial progress. We aimed to characterize the culling process in US dairy herds, including the main reasons for animal removal. Data from the Council on Dairy Cattle Breeding (CDCB) included 5.6 million records from average 2,630 herds (2006-2017), containing productive, reproductive, and culling information. Total longevity indicators were defined, and cows were stratified by pregnancy status, parity, production level, lactation stage, and region. Herds with fewer than 100 records and fewer than 5 culling codes were excluded. Animal destination was classified into 8 categories, allowing estimation of overall and cause-specific culling frequencies. A Cumulative Incidence Function (CIF) analysis was performed to compare the different reasons for culling. Mean longevity was 4.2 years and the overall culling rate was 31.03%, with "other or injury" (24.52%) as the most frequent reason, followed by "reproductive problems" (16.73%) and "died" (15.82%). However, this dynamic varies over the years; for younger animals, the primary reason for removal of herd was "dairy purposes," whereas reproductive problems had the least impact on the culling rate. Non-pregnant cows showed much higher culling rates than pregnant cows (54.88% vs. 12.19%), and dynamics varied across lactation stages. Multiparous cows were more affected by "died," "mastitis," and "feet and legs," whereas primiparous cows were more frequently removed of herd for "dairy purposes." Across regions and breeds, overall culling rates were similar, although culling profiles differed. Lower-producing animals exhibited higher culling rates, mainly due to involuntary causes, whereas more productive herds recorded more economically driven removals. The primary reasons for removed of herd also differed over the years; Sold for "dairy purposes" was more significant initially, whereas "other or injury" and "reproductive problems" became more important as the animals remained in the herd.