Replacing rapeseed meal with faba bean or lupin seeds in finishing diets for Holstein-Friesian bulls: Effects of tannins on beef quality and fatty acid composition

This study examined the effects of replacing rapeseed meal with faba bean seeds containing condensed tannins or with tannin-free white lupin seeds in finishing diets for Friesian bulls on beef quality and fatty acid composition. Thirty bulls were fed isoenergetic and isonitrogenous total mixed rations differing only in the protein source for 5 months, after which meat quality traits and the fatty acid profile of intramuscular fat were evaluated in the longissimus lumborum muscle. Although intramuscular fat content was similar among treatments (approximately 3%), the protein source markedly influenced the qualitative composition of muscle lipids. Diets containing faba bean resulted in a distinct fatty acid profile characterised by altered proportions of biohydrogenation intermediates, particularly trans C18:1 isomers, compared with rapeseed meal. The differences observed among dietary treatments may reflect combined effects of dietary fatty acid supply and diet-related changes in ruminal lipid metabolism. Although condensed tannins were present only in the faba bean diet, the similarity of several responses between faba bean and lupin indicates that the observed effects cannot be attributed specifically to tannins. Dietary protein source also affected selected sensory-related attributes of beef without altering colour after ageing, and selectively modified the concentrations of certain minerals and fat-soluble vitamins. Together, these results demonstrate that replacing rapeseed meal with legume seeds modifies beef quality primarily through changes in fatty acid composition rather than through differences in fat deposition, indicating that dietary protein source influenced lipid metabolism, with the observed responses likely reflecting a combination of differences in nutrient composition and possible effects of condensed tannins.