Survival rates and productive herd life of dairy cattle in the United States.

Survival rates and productive herd life were examined for 13.8 million US dairy cows that calved from January 1, 1980, through March 2, 2005. Cows that left the herd for dairy purposes or were from herds that discontinued Dairy Herd Improvement testing were excluded from any calculations to prevent underestimation of population longevity. Mean lactation length for cows without subsequently recorded lactations ranged from 205 to 235 d across breed-parity subsets and were 4 to 29 d longer for parities 2 through 7 than for parity 1. Mean survival rates were 73% to parity 2; 50% to parity 3; 32% to parity 4; and 19, 10, 5, and 2% to parities 5 through 8, respectively. The mean number of parities for Holsteins declined from 3.2 for those first calving in 1980 to 2.8 for those first calving in 1994. Mean numbers of parities for other breeds first calving in 1994 were 2.9 for Ayrshires and Brown Swiss, 2.4 for Guernseys, and 3.2 for Jerseys. Breed means for productive herd life (through parity 8) ranged from 28 to 36 mo. All regressions of mean number of parities or mean productive herd life on year were negative. The trend for decline of many of those indicators of longevity slowed or ended after the early 1990s. Between 31 (Jersey) and 39% (Guernsey) of herds were made up of first-calf heifers.