Approach to Underlying Causes of Heifersʹ Sub-optimum Performance in a Dairy Farm: Limitations in Using Non-local Reference Values

An interventional study was conducted on 19 Holstein heifers, with low weight gain and no clinical sign of disease, in a dairy farm in Fars province, Iran, regards to diagnosis and treatment of sub-optimum performance (SOP). RBC, WBC, PCV, hemoglobin, and serum glucose, cholesterol, triglycerides, total protein, globulins, ceruloplasmin and some minerals of the heifers were compared with published reference values. RBC, WBC, hemoglobin, glucose and total protein were within the reference intervals. Other parameters, however, revealed nutritional deficiencies and sub-clinical infections. The young stock was subjected to some management and nutritional interventions including regrouping of heifers, redesigning of barns and mangers and rebalancing the rations to correct intakes of dry matter, energy and protein, with no antibiotic prescription for 7 months. The same parameters were studied in the same heifers two more times in months 3 and 7. RBC, WBC and glucose did not show significant changes during the study. Alpha, beta and gamma-globulins decreased by time (P<0.01). All other parameters, however, increased (P<0.01) despite that some of them were initially within the reference intervals. Average daily gain (ADG) also increased but the difference was not significant (P<0.095). For investigating SOP, measuring selected parameters (particularly blood values) and comparing them to published reference values may be misleading and intensive investigations may be required. Establishing/re-establishing regional reference values by examining "well performed", "clinically healthy" animals are suggested