Stefan Yerby, James Huntington, Nicholas N Jonsson, Helen Warren
Abstract This Research Paper tested the hypothesis that the dietary inclusion of a fermentation product of Aspergillus niger (ANP), alone, or in combination with a mannan-rich fraction (MRF) derived from Saccharomyces cerevisiae cell wall, would enhance dairy calf performance and rumen variables. Thirty Holstein–Friesian bull calves (age 19 ± 5 days) were obtained from a single farm and randomly assigned according to days of age to one of three dietary treatment groups and one of two cull dates, experimental day 27 (immediately prior to weaning) or experimental day 70. Dietary treatment groups were: CTRL, no treatment; ANP, 3 g/day ANP; MRF, 3 g/day ANP and 2 g/day MRF. Calves were housed and fed individually and had ad libitum access to starter concentrates, water, and straw. Throughout the trial, ANP calves consumed a greater quantity of solid starter feed than CTRL and MRF calves. Body weight, average daily gain, apparent total tract dry matter digestibility and faecal scores were unaffected by treatment. Calves fed ANP and MRF had improved feed conversion efficiency compared with CTRL in some weeks, but this was not consistent throughout the pre-weaned and weaned periods. Calves fed MRF had a decreased acetate to propionate ratio compared with CTRL pre-weaning, and ANP had a lower acetate to propionate ratio and higher propionate proportion of total VFA compared with CTRL post-weaning. At both culling timepoints, ANP and MRF had thicker stratum basale, stratum spinosum and stratum granulosum in their rumen papillae compared with CTRL. The inclusion of ANP and ANP + MRF could favourably alter rumen fermentation and increase the metabolic and absorptive capacity of papillae in transition stage dairy calves but no consistent effects of treatment on calf growth or feed efficiency were observed in this trial.