Introduction The study determined the effects of different forms of phosphorus deficiency on white blood cell parameters in cows during the periparturient period and on the cows’ immune status. Material and Methods Thirty-two Holstein-Friesian cows aged 3–6 years were divided into four equal groups (I – control group, II – cows with atypical hypophosphataemia, III – cows with post-parturient haemoglobinuria and clinical hypophosphataemia and IV – cows with periparturient recumbency and clinical hypophosphatemia). The experiment used antibodies against CD4+ and CD8+ T cells (TCD4+ and TCD8+), CD21+ B cells (BCD21+) and major histocompatibility complex class II (MHC II). Immunophenotyping was performed by flow cytometry. The morphological examination determined the white and red blood cell and platelet counts, haemoglobin, haematocrit, mean corpuscular volume, mean corpuscular haemoglobin and mean corpuscular haemoglobin concentration. Microscopy of manual smears was performed to ascertain the percentage of leukocytes which was each of the granulocyte, segmented granulocyte and lymphocyte subpopulations. Results The TCD4+ lymphocyte subpopulation was larger in diseased cows and the largest in group IV animals. The TCD8+ lymphocyte subpopulation was smaller in hypophosphataemic Holstein-Friesians, and the smallest in group II. The CD4 : CD8 lymphocyte ratio in all diseased animals was higher than that in the control group, peaking in group II. Expression of MHC II protein was higher in affected than in healthy animals. The BCD21+ lymphocyte subpopulation was larger in diseased animals. Conclusion Long-term (even minor) phosphorus deficiency in an atypical form affects bovine cellular immunity (CD4 :CD8 ratio). In formerly affected cows, infectious diseases are more likely, even after their inorganic phosphorus level has been restored. Despite the less marked symptoms in animals with atypical hypophosphataemia, such animals have increased susceptibility to infectious agents and greater disturbance in their immune parameters.