The use of frozen equine faeces to assess the nutritional quality of forages using an in vitro gas production technique

Abstract

The in vitro gas production technique (IVGPT) is used to evaluate the nutritional quality for forages. The methodology for the IVGPT uses freshly collected microbial inoculum as an alternative to caecal fluid, but freshly voided faces cannot always be obtained. Using frozen faeces as inocula for the IVGPT would provide flexibility to this technique. However, information on using frozen inocula in gas production (GP) studies is limited. The aim of this study was to evaluate the use of frozen equine faeces as inocula for an IVGPT to assess the nutritional quality of forages. Two in vitro experiments were conducted. In experiment 1, high-temperature dried alfalfa (HTA) and mature grass hay (GH) were incubated with a faecal inoculum prepared either fresh (Fr) or following storage at -20 °C for 7 days (F7). In experiment 2, HTA, GH, high-temperature dried grass (HTG), and unmolassed sugar beet pulp (SB) were incubated with an inoculum prepared either fresh (Fr) or following storage at -20 °C for 24 hours (F24). In both experiments, GP values revealed an interaction (P<0.05) between inocula and substrate. GP from HTA was less affected by inocula source compared to all other substrates. In experiment 1, total GP was reduced by 33% for GH inoculated with F7, compared to 3% for HTA, whilst in experiment 2, total GP was reduced by 47, 37, 14 and 8% for GH, HTG, SB and HTA, respectively when inoculated with F24 compared to fresh faeces. The rate of GP was also affected by inocula source in both experiments. The use of frozen feaces as source of inocula affects the extent and rate of substrate fermentation in vitro, which appears to be dependent upon the nature of substrate assessed.