Parity and season affect hematological, biochemical, and milk parameters during the early postpartum period in grazing dairy cows from high-tropics herds

Improving the early detection of animals or herds at increased risk for diseases, reduced milk yield or impaired reproductive performance should be an essential component of herd health programs. The present study aimed to describe the findings of hematological, biochemical, and milk analytes of grazing cows from tropical dairy herds during the early postpartum period, and the effects of parity and calving season. In the North of Antioquia, Colombia which is the major area of specialized dairy production in the country, a longitudinal study comprising 260 dairy cows selected at calving, was conducted. Blood and milk sampling were made to establish red blood cell count, white blood cell count, minerals, protein traits and, milk composition. Variables were checked for normal distribution. The Box-Cox transformation was used when necessary. Variables were statistically analyzed using a GLM model considering parity and calving season as fixed effects. Using a parametric or non-parametric method based on the distribution of the variables, single average values, and 90% confidence intervals were determined considering fixed effects founds in the GLM model. Blood values affected by parity in lactating dairy cows grazing in highland tropical herds included serum calcium levels, red blood cell counts, hematocrit, hemoglobin, mean corpuscular hemoglobin, and total eosinophil counts, whereas blood values affected by season included: total leukocyte counts, total and differential lymphocyte counts, serum albumin and globulin concentration, and serum albumin:globulin ratio (P < 0.05). Data from our study could be used for comparison studies between lactating dairy cows within tropical herds or between tropical and seasonal dairy herds.