Can meteorological variables affect milk production in different lactation orders of dairy cows in the Cfb climatic zone? A case study in Southern Brazil.

Abstract

Data from 5689 lactating cows in 35 different dairy herds in Southern Brazil were evaluated over a 15-year period to examine the influence of meteorological variables on milk production in dairy cows with primiparous (1st) and multiparous (2nd to 4th) lactation. Meteorological variables considered were maximum and minimum temperature, relative humidity of air, solar radiation, wind speed, precipitation and temperature and humidity index corrected for solar radiation and wind speed (THIc). Data were submitted to principal component analysis (PRINCOMP), Pearson correlation (CORR) and step-by-step (STEPDISC) discriminant analyses, using the Statistical Analysis System (SAS®). lactation order and milk production showed a negative and significant correlation with minimum temperature, but with low magnitude. Primiparous and multiparous cows were negatively affected by maximum temperature in summer, while the higher the minimum temperature in winterwas, the better the milk production was. Primiparous cows produced, on average, 28.17 kg/day of milk and were 26.15 months old while the multiparous cows in average produced 30.76 kg/day and were 54.47 months old. The greatest average maximum temperature recorded during the 15 years of observations did not exceed 30oC and the THI corrected were maintained within acceptable values for animal thermal comfort. Lactation order and milk production showed a negative and significant correlation with minimum temperature, but with low magnitude. Milk production of multiparous cows was negatively affected by maximum temperature in summer and milk production of both categories were affected negatively by minimum temperature in fall. The principal component analysis did not show any association between milk production, lactation order and meteorological variables. Discriminant analysis presented significant values for meteorological variables, but with very low values of partial R2 estimated. Meteorological variables in a Cfb climatic zone did not negatively affect milk production in primiparous and multiparous lactating cows.