Comparison of lipid profiles in the faeces of beef cattle fed three common temperate grass silage diets and their relevance to dietary composition

Faecal lipidome signatures may vary depending on diet. Analyzing 17 different lipidome compounds and calculating ratios between them, we analysed the composition of faecal lipidomes (fatty alcohols, stanols, and archaeol) of beef cattle fed different diets. In this study, we measured the faecal lipidome profiles of beef cattle fed three types of grass silage representative of United Kingdom grasslands by gas chromatography-mass spectrometry. The forage consisted of 1) permanent pasture (sown perennial ryegrass mixed with unsown species); 2) reseeded perennial ryegrass monoculture; and 3) reseeded mixture of perennial ryegrass and white clover (ca 80:20 fresh weight). The contents of three forages varied significantly in water-soluble carbohydrates, acid detergent fibre, neutral detergent fibre, modified acid detergent fibre, crude protein, metabolizable energy, and crude ash. Diet significantly affected the composition of the faecal lipidome. Apart from stigmasterol, sex and the diet-by -sex interaction did not affect the faecal lipidome. Further, the ratios of lipidome compounds in faeces were validated as biomarkers of diet composition. The 24-ethyl coprostanol, 5-stigmastanol, campesterol, and even chain fatty alcohols such as C18-OH (3-hydroxy stearoyl carnitine), C22-OH - alcohol fraction with 22 carbon residues, C24-OH - alcohol fraction with 24 carbon residues, C26-OH - alcohol fraction with 26 carbon residues, and various lipidome ratios differed significantly between diets on a univariate basis. Based on an analysis of the composition and ratios of faecal lipidomes, this study provides a means for predicting the diet composition of agricultural livestock and wild herbivores.