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Circulating Blood Urea Nitrogen and Glucose Concentrations of Neonatal Beef Calves during the First 72 Hours
The objective of this study was to determine changes in neonatal calf serum blood urea nitrogen (BUN) and plasma glucose concentrations during the first 72 h postnatally and their relationship with calf birth weight. A total of 66 fall-calving beef cows and heifers were monitored during calving, and calf blood samples were obtained from a subset (n = 24; average age = 4.4 ± 0.5 yr; average BCS = 5.2 ± 0.1; average calving date = September 11, 2015). Jugular blood samples were obtained from 8 bull and 16 heifer calves at 0, 6, 12, 24, 48, and 72 h postnatally for serum BUN and plasma glucose analysis. Samples at 0 h were obtained prior to colostrum intake but after standing, and calf birth weight was collected at 14.0 ± 2.3 h. Serum BUN was analyzed using a commercially available kit based on the diacetylmonoxime method. Another commercial kit based on the glucose-6-phosphate dehydrogenase method was used to analyze plasma glucose. Data were analyzed using sampling hour as a fixed effect. Correlations of birth weight and circulating metabolite were determined for each sampling hour. There was an effect of hour (P < 0.001) on serum BUN, where BUN increased (P < 0.001) from 0 to 6 h, but was similar (P = 0.49) from 6 to 12 h. From 12 to 24 h, serum BUN increased (P = 0.04), but there was no change (P > 0.10) in BUN between 24 and 72 h. Sampling hour also affected (P < 0.001) plasma glucose. There was an increase (P ≤ 0.001) in plasma glucose from 0 to 24 h. Glucose concentrations were similar (P = 0.59) between 24 and 48 h, then tended to increase (P = 0.09) from 48 to 72 h. Calf birth weight was positively correlated with BUN at 6 h (r = 0.49, P = 0.03) and 12 h (r = 0.51, P = 0.04) and tended to be positively correlated at 24 h (r = 0.36, P = 0.10). There was no relationship between calf birth weight and serum BUN at 0, 48, or 72 h (P ≥ 0.12) or glucose at any hour (P ≥ 0.36). In conclusion, circulating BUN and glucose in beef calves increase during the first 24 h postnatally. Serum BUN concentrations positively correlate with birth weight at some hours of neonatal life, and therefore may indicate pre- or postnatal nutrient supply.
Keywords: beef calves, metabolites, parturition