Effect of diet on the partitioning of amino acids between body components of growing beef cattle fed at similar level of metabolisable energy intake

Eighteen Hereford × Friesian steers were reared from approximately 155 to 250, 350 and 500 kg live weight on either grass silage alone or a mixture of grass silage and concentrate (60:40 on metabolisable energy basis) in a comparative slaughter experiment designed to determine the amounts of individual amino acids (AA) accreted in different body components during growth. The dissected and bulked fractions were: head, hide, feet and tail; heart and lung; intestinal tissues; liver and gall bladder; non-carcass fat depots; bladder and kidney; and carcass. Nitrogen (N) accretions in the empty body weight between 250-500 kg were linear and no significant differences between diets were detected for total body-N at each slaughter point. This was reflected in a linear accretion of total and essential AA in the EBW in each fraction. The main difference between feeding all forage, silage compared to silage and concentrate was to increase the rate of tissue accretion, but it did not influence the accretion of AA in the total body or in various organs and tissues at selected empty body weights.