Cow Mortality in Midwest Dairy Herds

On-farm dairy cow mortality is becoming a significant issue in the US dairy industry. A rise in on-farm mortality among cows indicates compromised cow welfare and also causes economic losses, including value of animal, its replacement cost, the loss of milk production and the extra labor used for its carcass disposal. Recently published studied showed increasing trends in dairy cow mortality in the US and in other countries. Mortality is the primary reason of cows leaving the herd. Various herd and cow level factors have been associated to the rise in mortality over the last couple of decades.;The aim of the current study was to describe the mortality patterns among cows in Midwest dairy herds and to identify the cow and herd level risk factors for on farm mortality. Approximately 5.9 million lactation records for cows from 10 Midwest states that calved between January 2006 and December 2010 were analyzed. Herd level mortality rate increased over time, and was higher in larger herds, herds with lower milk yield, and herds with less annual culling. Cow level mortality rate was higher in early lactation, in older cows, in winter and summer. Also, mortality was the main reason of cows leaving the herds in our study. The survival analysis indicated that the hazards of mortality were higher in cows with higher fat to protein ratio, higher fat%, lower milk protein %, higher 1st test day somatic cell score, higher milk urea nitrogen, cows with male calves, cows carrying multiple calves, and increased calving difficulty score. Cow mortality was higher in herds with increased percentage of still births, herds with higher somatic cell score and increased herd calving interval, and larger herds. Cows with higher 1st test day milk yield and in herds with higher milk yield had lower mortality hazards. The results of current study indicate that first test day records especially those indicative of negative energy balance in cows could be helpful to identify animals at high risk of mortality. It was also noted that higher milk yield did not seem to have harmful effects on mortality. In addition, the association between herd level factors and mortality indicated that management quality could be an important factor in lowering on-farm mortality thereby improving cow welfare.