Influence of free fatty acid content on the feeding value of yellow greasein finishing diets for feedlot cattle

Holstein steers (n = 96; 375 kg) were used in a 144-d growth-performance tr ial to evaluate influence of level (42, 28.5, and 15%) of FFA content on fe eding value of yellow grease. Two sources of yellow grease were compared: c onventional yellow grease (CYG), containing 15% FFA, and griddle grease (GG ), containing 42% FFA. Dietary treatments consisted of an 88% concentrate f inishing diet supplemented with either 1) 0% fat, 2) 5% GG, 33 2.5% GG and 2.5% CYG, or 4) 5% CYG. Fat supplementation increased ADG (11%; P < .05), f eed efficiency (9%; P < .05), diet NE (6.4%; P < .05), carcass weight (4%; P < .10), dressing percentage (1%; P < .10), and kidney, pelvic, and heart fat (20%, P < .05). Increasing the FFA in supplemental fat increased (linea r effect, P < .10) DM intake, ADG, and feed efficiency and decreased (linea r effect, P < .10) retail yield. These improvements in performance were pri marily due to increased DM intake. The NE, and NE, values of supplemental f ats were not affected by FFA content, averaging 4.98 and 3.85 Mcal/kg, resp ectively. Treatment effects on characteristics of ruminal and total tract d igestion were evaluated using four Holstein steers (180 kg) with cannulas i n the rumen and proximal duodenum. Supplemental fat did not influence (P > .10) ruminal or total tract digestion of OM, ADF, starch or N. Postruminal fatty acid digestion was less (P < .10) for fat-supplemented diets than for unsupplemented diets (73.0 vs 78.6%). The decrease in postruminal fatty ac id digestibility with fat supplementation was mainly due to a decreased (16 .7%; P < .05)digestibility of C 18:0. Postruminal digestibility of the supp lemental fat was 68%. There were no treatment effects (P > .10) on ruminal pH. Ruminal biohydrogenation of fatty acids was directly proportional to es timates of methane production. We conclude that the feeding value bf conven tional yellow grease and griddle grease is similar and that differences in the FFA content of yellow grease;will not negatively affect diet acceptabil ity and growth performance of feedlot cattle.