Milk urea concentrations and pregnancy rate in dairy cows and a comparison of a dip-stick method and a laboratory method to measure milk urea concentrations

Abstract

AbstractThe first study was conducted to investigate the possible relationship between milk urea concentrations and pregnancy rate in dairy cows. A total of 173 dairy cows were used in the study. They had not experienced reproductive problems post partum, however they were treated for suboestrus between 60 to 90 d post partum with either PGF2α or GnRH, PGF2α and GnRH. Suboestrus cows were studied in this experiment in order to see whether, when ovulation is initiated, high milk urea concentrations were associated with a poorer response to treatment. Milk samples were collected on the day of AI, for the measurement of urea concentrations, and pregnancy diagnosis was performed by the assay of Pregnancy Specific Protein Binding (PSPB) 50 d post-AI. Peak milk production (P=0.06), the type of diet (P=0.05), the main forage type (P=0.07) and the concentrate distribution system (P=0.03) influenced milk urea concentrations. There was no difference in the concentrations of urea in the milk of pregnant and non-pregnant cows (P = 0.33, 0.25 g L-1 vs. 0.27 g L-1, respectively). Pregnancy rate was not influenced by the type of suboestrus treatment used. A second experiment showed that there was a linear relationship between milk urea concentrations measured by a dipstick method (Azotest) and a laboratory method (r=0.51, P<0.001, n=89)