Effects of dietary L-carnitine and dried distillers grains with solubles on growth, carcass characteristics, and loin and fat quality of growing-finishing pigs

A total of 1104 barrows and gilts (PIC 337 x 1050, Pig Improvement Company, Hendersonville, TN), weighing 36 +/- 1 kg were used in a 109-d study to evaluate effects of dietary L-carnitine and dried distillers grains with solubles (DDGS) on growth, carcass traits, and loin and fat quality. Pigs were blocked by BW and randomly assigned to 1 of 6 treatments, with 7 pens per treatment. Treatments were arranged as a 2 x 3 factorial, with main effects of DDGS (30% in Phases 1, 2, and 3, and 20% in Phase 4) and L-carnitine (0, 50, or 100 mg/kg). Overall (d 0 to 109), dietary L-carnitine tended to improve ADG (linear, P = 0.07). Pigs fed 50 mg/kg L-carnitine but no DDGS had greater G:F than pigs fed 0 or 100 mg/kg, whereas when diets containing DDGS were fed, 50 mg/kg of L-carnitine reduced G:F compared with pigs fed 0 or 100 mg/kg (quadratic DDGS x L-carnitine, P < 0.01). There was no effect of DDGS x L-carnitine for any carcass traits, but pigs fed increasing dietary inclusion levels of L-carnitine produced heavier HCW (quadratic, P = 0.03), greater carcass yields (quadratic, P = 0.07), and greater fat depths (quadratic, P = 0.04), with the greatest response observed in pigs fed 50 mg/kg dietary L-carnitine. Feeding L-carnitine increased purge loss (linear, P = 0.03), whereas feeding DDGS tended to decrease (P = 0.06) LM marbling scores. The LM from pigs fed 50 mg/kg L-carnitine and DDGS had lower shear force values compared with LM chops from pigs fed either 0 or 100 mg/kg; however, shear force values were similar across dietary L-carnitine levels in diets devoid of DDGS (quadratic DDGS x L-carnitine, P < 0.01). Furthermore, increasing L-carnitine in DDGS diets increased fresh LM color scores, but pigs fed DDGS-free diets produced LM chops with similar subjective color scores (linear DDGS x L-carnitine, P = 0.03). As expected, feeding DDGS increased (P < 0.001) iodine value (IV) in jowl fat samples, but dietary L-carnitine did not alter IV. The concentrations of C18:2n-6 and C20:2 were decreased with increasing L-carnitine in DDGS-containing diets, but not in diets without DDGS (linear DDGS x L-carnitine, P <= 0.04). Results of this study indicate that dietary DDGS did not affect growth, but led to more unsaturation of jowl fat, whereas feeding 50 mg/kg of L-carnitine improved HCW and reduced C18:2n-6 in jowl fat when fed in combination with DDGS.