Seasonal Influences on Milk Yield and Composition Dynamics during a Normal Lactation in Dairy Cows. Milk Lactose, Solids Non Fat, Total Dry Matter Percentage

Researches were made on 125 lactations from Romanian Black Spotted cows, aimed at studying the evolution of the interval between calving on milk quantity and quality. Data were recorded and statistically analyzed by means of ANOVA/MANOVA determining the average values and dispersion indices. Based on averages parameters of lactation curves were calculated using the mathematical model proposed by Wood in 1967, called the incomplete gamma function. Lactation curve for lactose percentage was very different among seasons. Significant differences (p<0.05) were observed between summer-winter and spring-autumn, and distinct significant differences (p<0.01) between summer and spring. Flat pattern of the lactation curve for solids non fat percentage had the same shape for all seasons with distinct significant differences (p<0.01) between winter and autumn and very significant differences (p<0.001) between summer and autumn and spring and autumn.