The data demonstrate that mild fatty liver is associated with decreased general health and reproductive performance as evidenced by more days to first estrus and service, more days open, decreased conception, increased number of days with elevated body temperature at days 9 - 22 postpartum, and increased incidence of mastitis at days 32 – 150 postpartum. The latter two were decreased in dairy cows with mild fatty liver injected with 15 mg/d of glucagon during weeks 2 and 3 postpartum. Therefore, treatment of mild fatty liver with exogenous glucagon or better prevention of fatty liver might improve health and reproductive performance of lactating dairy cows, thereby preventing loss of income of dairy farmers.