Infestations of winter ticks, Dermacentor albipictus (Packard), observed on mature black Angus cows, reached peak levels in January and diminished through March. Infestations of adult lone star ticks, Amblyomma americanum (L.), began in mid-January and increased through May. Cows receiving Ectrin, Taktic, or Deltox treatments on 13 December and 21 February experienced significantly less weight loss and entered the subsequent breeding season with higher average body weight than untreated cows. In a separate study, lactating Brangus and Brangus-cross cows, equally infested by natural populations of these ticks, were provided five supplement treatment regimens, fed individually with quantities adjusted for body weight and condition score. Groups receiving supplementation highest in crude protein and digestible energy lost significantly less weight and experienced the least amount of deterioration in body condition. Performance among these groups was influenced by the amount of digestible energy and the period in which increased levels of digestible energy were fed. Cows receiving the supplement highest in protein coupled with an increase in digestible energy from 10 to 60 Mcal/kg W0.75 on 16 January experienced the smallest average change in condition score and weight parameters.