Thi Thuy Ngo, PhD candidate, Thesis Review Seminar, ‘Role of probiotic Bacillus amyloliquefaciens strain H57 in regulating the dietary preference of ruminants’

Thi Thuy’s advisors are Dr David McNeill, Dr Peter Dart, and A/Prof Athol Klieve

Abstract

Often a proportion of ruminants in a group refuse to eat an unfamiliar feed regardless of how nutritious it is for them and so can fall behind their peers in productivity and health. A probiotic feed inoculum, Bacillus amyloliquefaciens strain H57 (H57) has recently been shown to increase feed preference and feed intake in weaned calves and pregnant ewes. However, the mechanisms explaining the link between H57 and enhanced diet preference remains unclear. The aim of this PhD project was to investigate the signals from ruminal fermentation and food sensory characteristics that could explain why cattle increase their preference for feedlot pellets following the incorporation of H57 into the pellets.

H57 consistently improved feed preference of mature steers and weaned calves for feedlot pellets across the 4 studies conducted. In steers, H57 advantaged fermentation processes of the rumen by increasing ruminal pH and the concentrations of iso-butyrate or iso-valerate, and tended to improve ruminal ammonia and butyrate. However, these responses were not directly related to diet preference. By contrast, in weaned calves, preference for H57 inoculated feedlot pellets was associated with an apparent ability of the H57 to reduce the rate of microbial spoilage, as indicated by microbial VOC profile changes, over a 3 - 4 month storage at ambient temperature. Thus, the results are consistent with the hypothesis that H57 influenced preference by maintaining odours of H57 inoculated pellets. The candidate microbial VOCs that may act as pre-ingestive signals that should be considered in future experiments as drivers of feed preference.

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