Rumen Morphology Measurements in Periruminant Holstein Bull Calves Fed a Fermentation Extract of Aspergillus oryzae
Age and diet not only affect calf BW, they can impact rumen growth and development too. A fermentation extract of Aspergillus oryzae has previously been utilized as a direct fed microbial (DFM) to increase rumen bacterial numbers and promote starter intake in calves. Effects of feeding an extract of A. oryzae on rumen morphology in periruminant calves are largely unknown. Objectives were to determine if age and dietary inclusion of an extract of A. oryzae affect: organ size, muscle and sub-mucosal thickness of rumen tissue, and papillae area in periruminant Holstein bull calves. Individual calves (n=52) were randomly assigned to a slaughter age, 4wk (n = 16) or 8wk (n = 36), and treatment, control (CON; n = 27) or DFM (n = 25). Calves were housed and fed individually; no bedding was used. Liquid DFM was delivered in milk replacer (2 g per day) for the first 4 wk of the trial; solid DFM (2 g per day) was top-dressed on grain thereafter. Calves were fed non-medicated milk replacer twice daily (22.0% CP, 20.0% fat DM basis; 680 g/d) and had ad libitum access to texturized grain (20% CP, 2.0% fat) and water. Treatment and the interaction of treatment and age did not affect full or empty rumen weights. However, full and empty rumen weights were greater at 8wk (5.29±0.21and 1.31±0.04 kg, respectively) than 4wk (1.81±0.30 and 0.52±0.06 kg, respectively). Muscle thickness (894.15±69.50 μm, 4wk; 1098.58±47.64 μm, 8wk) and sub-mucosal thickness (247.57±43.48 μm, 4wk; 583.67±29.80 μm, 8wk) were both affected by age, but not by treatment or interaction. Lastly, within the cranial ventral region of the rumen of 8wk old calves (4wk samples not measureable), treatment had no effect on papillae area (6.52 ±0.39 mm2, CON; 6.65±0.41 mm2 DFM). In summary, dietary inclusion (2g/d) of an extract of A. oryzaedid not affect rumen morphological development when supplemented animals were compared to cohorts not fed DFM. It is possible that the dose used here was not high enough to elicit treatment effects. Evaluation of other measures of performance, such as calf growth, may add further information on the efficacy of this DFM in periruminant calf diets. A higher dose of DFM may yield different effects.
dairy calf, rumen, direct fed microbial