The impact of nutrition and non nutrition factors on milk urea concentration. II. The impact of non nutrition factors on milk urea concentration

Title of the paper: The impact of nutrition and non nutrition factors on mi lk urea concentration. II. The impact of non nutrition factors on milk urea concentration The object of this study was to determine the impact of non nutrition facto rs stage of lactation, parity, milk protein yield, somatic cell count, seas on and herd on milk urea concentration. For parity one to fife 239, 242, 23 8, 235 and 237 mg urea/l milk was calculated using least-squares-means. Par ity has a statistical significant but small influence on the milk urea conc entration. There was a strong positive relationship between the stage of la ctation (day in milk) and milk urea concentration. The regression coefficie nts for day in milk within the three lactation periods were 0.34, 0.04 and 0.06. This means that the milk urea concentration increases by about 10 mg/ l over 30 days in the first lactation period. The fixed effects for first a nd second lactation period versus third lactation period were -31.6 and -2. 1. Protein yield has a significantly positive influence on milk urea concen tration. The regression coefficients for milk protein yield within the thre e lactation periods were 42.5, 43.2 and 31.2. This means that the milk urea concentration would increase by about 4 mg/l in first lactation period if the milk protein yield increased by 0.1 kg/day. The effect of somatic cell count on milk urea was significantly negative. The regression coefficients for somatic cell count within the three lactation period were -0.017, -0.01 9 and -0.015. This means that the milk urea concentration will decrease by 1.7 mg/l in first lactation period if the somatic cell count increases by I E5/ml. The relationship between dietary crude protein/energy balance, milk protein yield, stage of lactation, somatic cell count and milk urea concent ration can be described by an equation (third paper).