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Mortality and herd turnover rates in large dairy herds in the Upper Midwest USA
The objectives of this study were to describe mortality and herd turnover rates in large Upper Midwest dairy herds, and evaluate the association between breed and mortality rates. The study included 15 dairy farms in Minnesota, Wisconsin, Iowa, and South Dakota. All farms had over 2,500 lactating cows housed in a freestall system. Twelve of the farms had Holstein cows, 2 farms had Jersey cows, and 1 farm had Jersey and Holstein crosses. Herd size (mean ± SD) was 4,972 ± 2,652 cows with a range of 2,600 to 13,250 cows. On farm records were obtained for 2 years on each farm from July 2011 to July 2013. Sold and died events were examined from the on farm record keeping system to determine mortality and herd turnover rates. Herd turnover rate was calculated as the number of animals that were sold or died during a 1-yr period, divided by the average herd size during that 1-yr period. Mortality rate was calculated as the number of animals that died during a 1-yr period, divided by the average herd size during that period. Overall mortality rate was 7.4 ± 2.1%. Deaths on farm were categorized as injury, mastitis, lameness, sickness, down cow, transition diseases, dystocia, euthanasia, miscellaneous, or unknown reasons. Main causes of death were sickness (33.5 ± 17.3), unknown reasons (15.3 ± 24.6), and injury (11.1 ± 10.6). Overall herd turnover rate was 41.6 ± 5.9%. Reasons for turnover were categorized as low production, lameness or injury, mastitis, reproduction, transition problems, abortion, udder conformation, sickness, miscellaneous, or unknown reasons. Main reasons for turnover were low production (30.0 ± 22.0), mastitis (16.4 ± 11.9), and sickness (12.7 ± 5.2). Turnover rate during the first 60 DIM was 8.3 ± 2.3%. The PROC MIXED in SAS was used to evaluate the association between mortality rate and breed (Jersey vs. Holstein). Breed was associated with yearly mortality rate (P = 0.038); mortality rates (LSMeans ± SE) were 5.3 ± 0.01 and 7.6 ± 0.003 for Jersey and Holstein herds, respectively. Mortality rate in the first 60 DIM was 3.1 ± 0.003 for Holstein and 2.2 ± 0.01 for Jersey herds and there was no association with breed. Based on these results, Jersey cows appear to have lower overall mortality rates but similar early lactation mortality rates compared to Holstein cows in large freestall herds.
Keywords:
mortality rate, turnover rate, large dairy herd