Initial blood urea nitrogen concentration predicts subsequent blood urea nitrogen concentration in beef cows

Abstract

This study was performed to determine whether beef cows have an inherent ability to maintain their relative blood urea nitrogen (BUN) concentration when cattle are exposed to varying levels of dietary nitrogen supplementation. Ten Hereford and 11 Nguni cows, aged between 2 and 16 years, were utilised in two crossover designs. In the first design, cows were exposed to diets containing normal and high crude protein (CP) levels. At the end of the first crossover design, cows received a normal diet for one week before commencement of the second design. In the second crossover design, cows were fed diets containing normal and low CP levels. Blood urea nitrogen concentration was measured 17-21 times (mean = 20) during the study. A linear mixed-effects model was used to assess whether baseline BUN concentration (measured one week before onset of the study) was predictive of subsequent BUN concentration in individual cows. The model was also used to assess whether any of the measured variables were predictive of subsequent BUN concentrations. Baseline BUN concentration was a significant predictor of subsequent BUN concentration in individual cows (P = 0.004). Other variables that were significantly associated with subsequent BUN concentration were breed (P = 0.033), the diet that the cows received before the current treatment (P < 0.001), treatment (P < 0.001) and the week during which sampling was performed (P < 0.001). Beef cattle appear to have an inherent ability to maintain their relative BUN concentration within herds despite changes in levels of dietary nitrogen supplementation.