Effects of alfalfa particle size and starch content in diets on feeding behaviour, intake, rumen parameters, animal performance and meat quality of growing lambs

Thirty-two crossbred Merino branco male lambs were randomly allocated to eight diets, combining two forms of alfalfa presentation (chopped or ground), with four barley grain levels (0%, 11.2%, 21.3% and 33% dry matter (DM)), balanced by low starch agro-industrial by-products (LSBP). The diets were supplemented with 6% soybean oil and included 40% of alfalfa in DM. The lambs were individually housed and the trial lasted six weeks. Intake of DM, average daily weight gain (ADG) and carcass weight were higher with ground alfalfa (P < 0.01). Replacing barley grain by LSBP reduced linearly DM intake and ADG (P < 0.001) but increased meat tenderness (P = 0.046). Regardless of the treatments, meat showed a healthy biohydrogenation fatty acid (FA) profile, with high proportions of t11-18:1, c9,t11-18:2 and a t10-18:1/t11-18:1 ratio clearly below 1. The reduction of barley in diet had a moderate positive impact on meat FA composition, decreasing t10-18:1, which was enhanced by the increase of forage particle size.