Relationship between the blood composition of Friesian (Holstein) bulls and their improved contemporary comparisons for production traits

Blood samples were taken from 428 Friesian (Holstein) bulls on three occasions, on average at approximately 3-monthly intervals, between 3 and 15 months of age, and also from 214 of them on three occasions at 6-monthly intervals when they were between 2 and 6 years of age. The average concentrations of blood glucose and haemoglobin and of serum cholesterol, urea, albumin, globulin, inorganic phosphate, Ca, Mg, Na, K and Cu were calculated for each of these periods and correlated with improved contemporary comparisons of milk yield and quality. Repeatability estimates were similar within each of the two periods but were lower when mean concentrations calculated between 3 and 15 months of age were compared with those between 2 and 6 years. The main exceptions were cholesterol (0.52) and Cu (0.54) for which repeatability estimates were similar to those derived within the above two periods. The constituents with the next highest levels of repeatability were magnesium (0.44), globulin (0.43) and inorganic phosphate (0.39), which were approximately 30% lower than those obtained within the two periods. Correlations between blood concentrations and improved contemporary comparisons were negligible, indicating that it is not possible to use these blood constituents to predict the milk production potential of a bull's daughters. © 1986, Cambridge University Press. All rights reserved.