Health of Holstein Bull Calves Fed a Fermentation Extract of Aspergillus Oryzae
The objective was to determine whether dietary inclusion of a fermentation extract of the fungus Aspergillus oryzae, commonly used as a direct fed microbial, would improve measures of health in Holstein bull calves (n=52) from birth thru 1wk post weaning. Calves were randomly assigned to a slaughter age, 4 wk (n = 16) or 8 wk (n = 36) and treatment, control (CON; n = 27) or direct fed microbial (DFM; n = 25). Calves averaged 43.2 ± 1.0 kg BW and 2.8 ± 0.3 days of age at the beginning of the experiment. Calves were housed and fed individually; no bedding was used. Calves assigned to DFM were fed 2 g of DFM daily. Liquid DFM was delivered in milk replacer for the first 4 wk of the trial; solid DFM was top-dressed on texturized grain thereafter. Calves were fed non-medicated milk replacer twice daily (22.0% CP, 20.0% fat DM basis; 680 g/d) and were weaned upon consumption of 0.91 kg of grain (20% CP, 2.0% fat; medicated with decoquinate) for 3 consecutive days or on d 45 of the study, whichever came first. Calves had ad libitum access to grain and water throughout the trial. Calf fecal scores were recorded daily then averaged across treatment. On a weekly basis, DFM calves scoured more frequently than CON. All medical interventions (including oral electrolytes) were recorded. Treatment for respiratory ailments were more frequent in CON than DFM. Medical costs were calculated on a calf basis then averaged by treatment. Medical costs for calves from 0 thru 4wk ($43.01±2.40) and 5 thru 8wk ($11.18±2.40) did not differ by treatment. For 8wk calves, jejunal lymph nodes were collected upon slaughter for flow cytometric analysis of CD4 and CD8 T cell populations as a measure of immune function. The CD4 cell population as a percentage of total observed cells was greater in DFM calves. Treatment did not affect CD8 cell population as a percentage of total observed cells. Flow cytometric results indicate that DFM may affect the adaptive immune system through effects mediated by CD4 positive cells. In conclusion, calves fed DFM scoured more frequently, but a lesser percentage of DFM calves were treated for respiratory ailments leading to no effect on medical costs. Interestingly, CD4 cell population of jejunal lymph nodes was greater in DFM calves, which warrants further research.
Keywords: dairy calf, direct fed microbial, T cells