Effect of different levels of dietary nitrogen supplementation on the relative blood urea nitrogen concentration of beef cows
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The objective of this study was to determine if individual beef cows in a herd have an inherent ability to maintain their blood urea nitrogen (BUN) concentration when exposed to different levels of dietary nitrogen supplementation. Ten Hereford and 12 Nguni cows, aged between 2 and 16 years, were utilized in two crossover experiments. In the first experiment, cows were exposed to two diets: a balanced diet with a crude protein (CP) level of 7.9% and a modified diet with a CP level of 14%, formulated by adding 20 kg of feed grade urea per ton of the balanced diet. At the end of the first crossover experiment, cows received the balanced diet for 1 week. The second component utilized the same cows wherein they were fed the balanced diet in addition to another modified diet containing only 4.4% CP. Blood urea nitrogen concentration was measured 22 times (twice weekly) from each cow during both components of the study. A linear mixed-effects model was used to assess whether baseline BUN concentration (measured 1 week before onset of the study) was predictive of subsequent BUN concentration in individual cows. Breed, cow age, body condition score, and body mass were also evaluated for their effects on BUN concentrations. Albumin, beta hydroxybutyric acid (BHBA), glucose, and total serum protein (TSP) were compared between diets within each breed. Baseline BUN concentration was a significant predictor of subsequent BUN concentration in individual cows (P = 0.004) when evaluated over both components of the study. Breed (P = 0.033), the preceding diet (P < 0.001), current diet (P < 0.001), and the week during which sampling was performed (P < 0.001) were also associated with BUN concentration. Results suggest that beef cattle (within a herd) have an inherent ability to maintain their BUN concentration despite fluctuations in levels of available dietary nitrogen.
KeywordsDietary protein Beef cows Blood urea nitrogen Efficiency
The authors thank the farm management of the herds that were used in this study for supplying animals and farm records.
They would like to thank the Research Committee and the Department of Production Animal Studies at the Faculty of Veterinary Science, University of Pretoria for providing financial support and facilities (2014).Also, the authors would like to thank the Gauteng Department of Agriculture and Rural Development (2014) for financial support.
Compliance with ethical standards
Informed consent (written) was obtained from all participating herd owners prior to commencement of the study.
Conflict of interest
The authors declare that they have no conflict of interest.
Statement of animal rights
The protocol for this study was approved by the Animal Ethics Committee of the University of Pretoria (protocol number: V086-14) and adhered to the South African National Standard for the Care and Use of Animals for Scientific Purposes (SANS 10386:2008).
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