A study on the lactation curve characteristics and factors affecting them in dairy cows (case study: industrial dairy herds of Mashhad city)

Abstract

Introduction: The shape of lactation curve is unique for each cow and is affected by various genetic and non-genetic factors. Hence, its study in each cow and herd separately is important for making managerial decisions. Materials & Methods: In order to study the factors affecting lactation curve in Holstein dairy cows, 271509 test day milk records (milking three times a day) of 30997 primiparous cows which calved in 79 herds in Mashhad city, from years 1993 to 2015 were used. The incomplete Gama function fitted to records, using NLIN procedure of SAS. Effect of herd, year, month and age at first calving, percent of Holstein gene, average mean of daily humidity, average mean of daily temperature, minimum and maximum temperature on lactation curve parameters were studied using GLM procedure of SAS. Also, correlations of lactation curve parameters with each other and with climatic parameters were calculated using CORR procedure of SAS. Results: In studied herds lactation period began with producing 16.76 Kg milk daily and on day 88th reached the peak with 34.44 Kg yield and persistency was 7.43. Herd, year, month and age of calving and percent of Holstein gene had significantly affected the lactation curve (P<0.01). The trend of changing the level of initial milk yield, days to peak milk yield and the lactation persistency, was increasing through the studied years. Among the climatic parameters only average mean of daily temperature had significant effect on some lactation curve parameters. Conclusion: As genetic evaluation of dairy cattle moves toward the use of test day models, therefore investigating the factors affecting the shape of lactation curve in order to include them in the model and increase the accuracy of genetic parameters estimation is necessary.