The association of prepartum urine pH, plasma total calcium concentration at calving and postpartum diseases in Holstein dairy cattle

Abstract

The use of anionic salts to prevent milk fever in dairy cattle has been an effective nutritional strategy; however, the degree of acidification that determines the most acceptable productive responses andwell-being of the cowis still a controversial topic. The objective of this study was to assess urine pH in prepartum Holstein cows fed anionic diets and determine its association with plasma total Ca, Mg, P, beta-hydroxyl-butyrate (BHB) concentrations at parturition and the occurrence of peripartum disorders. This investigation consisted of 2 studies. Study 1 was conducted on a grazing dairy. Between February andMay 2019, 60 prepartum multiparous cowswere tested for urine pH and plasmametabolite concentration at parturition. Total Ca, P, Mg and BHB at day 1 inmilk (DIM) were assessed and statistically analyzed by ANOVA (models for polynomial regression). Study 2 was conducted on a drylot dairy farm. Between July 2018 and January 2019, 203 cows were evaluated for urine pH and followedup for 30 DIMto obtain the incidence of dystocia, stillbirths, milk fever, retained fetal membranes, metritis, clinical mastitis and ketosis. Cows were categorized based on their last urine pH as group 1: pH > 7.0 (n = 135); group 2: pH between 6.0 and 7.0 (n = 46) and group 3: pH < 6.0 (n = 22). A logistic regression model for each health event was conducted considering urine pH group as the main effect. Urine sample was collected at 2.71 +/- 2.84 days before parturition. In study 1, there was a quadratic effect of urine pH on total Ca. Total Ca concentration was higher between urine pH 6.0 and 7.0, while decreasing below pH 6.0 and above pH 7.0. Therewas a trend (P= 0.11) for a quadratic effect of urine pH on the concentration of plasma BHB at parturition. beta-Hydroxyl-butyrate was lower approximately between urine pH 6.5 and 7.5. In study 2, the odds for a stillborn in cows with urine pH < 6.0was 2.39 (95% CI= 1.06-5.40) times the odds for a stillborn in cowswith urine pH = 7.0. Therewas no association between urine pHand the other diseases. In conclusion, cows with prepartumurine pH < 6.0 and >7.0 had lower concentration of plasma total Ca and tended to have a higher concentration of BHB. Cows with urine pH < 6.0 had a higher incidence of stillbirths than cows with urine pH > 7.0.