Calving causes cows to endure many physiological changes that require good nutrition, time, and adequate rest for recovery. Upon calving, cows are introduced into the lactating herd, where they consume high amounts of a new ration and have to adapt to a new feeding and milking routine. Lactation requires more support from the diet than pregnancy and weight maintenance, particularly in fresh cows calving in with a negative energy balance. Additionally, the social hierarchy within the herd is re-established every time a new cow enters the group, which can cause stress, especially for timid and weak cows. For these reasons, cows become immunosuppressed, making them more susceptible to illness. Although many cows seem to adapt quickly and adequately to this new period, underlying issues are often present that are sometimes difficult to notice.
Sterrett, Amanda E.; Amaral-Phillips, Donna M.; Bewley, Jeffrey M.; and Arnold, Michelle, "A Fresh Cow Health Monitoring System" (2014). Agriculture and Natural Resources Publications. Paper 166.