Abstract
The objective of this experiment was to evaluate the tolerance of fattening beef cattle to slow release urea (SRU). Twenty-four growing Holstein bulls were blocked by weight and randomly assigned to one of three treatments: CON (no urea) and SRU (Optigen®, Alltech Inc., KY) at 1% or 3% of the ration. Energy and crude protein levels were maintained in SRU diets by replacing soybean meal with SRU, barley meal and corn meal. Daily feed intake and body weights at d 0, 21 and 42 were registered. Blood was collected on d 0 and 42 for hematologic and biochemical analysis. Intake was analyzed using a linear mixed-effects model with repeated measures with initial body weight as a covariate. Blood data at d 42 were analyzed using a linear model with fixed effect of treatment including data of d 0 as covariate. Intake did not differ among dietary treatments (P > 0.1). Blood hematologic results for all treatments were within normal physiologic ranges. Compared with CON, bulls fed diets with SRU at 1% or 3% had lesser hemoglobin (13.0 vs.12.3, 12.3 g/dL; P = 0.028) and lesser packed cell volume (33.1 vs. 31.1, 31.2%; P = 0.007). Serum albumin concentrations differed between treatments, but values were within normal physiologic range (3.7, 3.4 and 3.6 g/dL, P < 0.01). Total protein values were significantly lesser in SRU containing diets versus CON (6.8 vs. 6.6, 6.5 %; P = 0.031) and slightly under the reference values. Serum ammonia concentrations were well below the toxic limit and did not differ among dietary treatments (P > 0.1). There was no evidence of ammonia toxicity during the study. Feeding SRU appears to be safe and well tolerated when included at up to 3% of the diet in Holstein bulls fed high-concentrate diets during a 6-wks period.
Keywords: cattle, rumen, urea