UC Davis

Lipid supplements are commonly used to increase the energy density of finishing diets, but their effects depend on how fatty acids interact with the basal diet and rumen environment. This thesis reviews the effects of lipid source, physical form, inclusion level, and basal diet on ruminant performance, carcass traits, meat quality, and meat fatty acid profile. It also evaluated relationships between trans(t)-10-shifted ruminal biohydrogenation and carcass fatness in feedlot-finished lambs and the effects of dietary induction of a t-10 shift. In the first experiment, 232 commercial lamb carcasses were evaluated, with backfat fatty acid profiles determined in 80 carcasses representing USDA Yield Grades 2-5. Backfat t10-18:1 (r = −0.50), trans-10,cis-12 CLA (t10,c12-CLA; r = −0.30), and the t10-18:1/trans-11 18:1 ratio (t10/t11; r = −0.54) were negatively correlated with Yield Grade, whereas t11-18:1 (r = 0.33) and cis-9,trans-11 CLA (r = 0.34) were positively correlated (P < 0.01). Based on these associations, a subsequent feeding trial was designed to experimentally induce a t-10 shift and examine potential cause-and-effect relationships between increased t-10 biohydrogenation intermediates, lipid metabolism, and carcass fatness. Twenty-four lambs were fed grain-based diets containing no added fat (CTL), 6% corn oil (COR), or 6% high-palmitic acid fat (PAL) for 35 days. The COR diet induced a pronounced t-10 shift, increasing t10-18:1 by ~400% in backfat and longissimus lumborum muscle and t10,c12-CLA by ~300% in backfat (P < 0.05). This treatment also reduced fatty acid synthase (FAS) mRNA expression in backfat (P < 0.05), indicating an effect on adipose lipogenic regulation. The COR diet reduced dry matter intake compared with CTL and PAL and improved feed efficiency compared with PAL (P < 0.05), without affecting weight gain or final body weight. Hot carcass weight was also increased in COR compared with CTL and dressing percentage compared with CTL and PAL (P < 0.01) but did not affect backfat thickness or Yield Grade. Dietary treatments also did not affect instrumental color, cooking loss, Warner-Bratzler shear force, or lipid oxidation (P > 0.10). Collectively, the survey identified an association between a greater t-10 shift and lower carcass fatness, whereas the controlled feeding trial demonstrated that dietary induction of a t-10 shift markedly altered tissue fatty acid composition and some aspects of lipid metabolism without reducing carcass fatness. The relatively short 35-d treatment period may have limited the time available for changes in lipid metabolism to translate into measurable differences in carcass fatness. Longer-term studies are warranted to determine whether sustained exposure to a t-10 shift and its biohydrogenation intermediates can ultimately influence carcass fat deposition.