Productive and physiological responses of feedlot cattle receiving different sources of Ca salts of fatty acids in the finishing diet.

This study evaluated productive and physiological responses in feedlot cattle receiving a finishing diet that included Ca salts of palm oil (CSPALM), or a blend of Ca salts of palm, cottonseed, and soybean oils (CSMIX). Ninety yearling steers were housed in 15 pens equipped with Calan-gate feeders (6 steers/pen). Steers within each pen were stratified by shrunk body weight (BW; 410 ± 3.3 kg across pens) on d 0 and assigned to receive a total-mixed ration (TMR) containing (dry matter basis) 2.2% of CSPALM (n = 30), 2.2% of CSMIX (n = 30), or no supplemental fat (CON; n = 30). Individual TMR intake was evaluated weekly. Blood samples were collected on d 0, 28, 56, 91, 119, and 147. Samples of the Longissimus muscle (LM) were collected on d 84 via biopsy. Upon slaughter on d 148, hot carcass weight (HCW) was recorded to estimate final BW (63% dressing), and one LM steak sample (2.54 cm thickness) was removed from the right side of each carcass. Steer ADG was greater (P = 0.02) for CSMIX compared with CSPALM and tended to be greater (P = 0.09) for CSMIX compared with CON. The gain:feed ratio was greater (P ≤ 0.05) for CSMIX compared with CSPALM and CON, and carcass LM area was less (P = 0.01) for CSPALM compared with CSMIX and CON. No treatment effects were detected (P ≥ 0.21) for TMR intake, final BW, and other carcass merit traits including marbling. Mean plasma cholesterol concentrations were greater (P < 0.01) in CSMIX and CSPALM compared with CON, and mRNA expression of adipocyte fatty acid binding protein in the LM on d 84 was greater (P ≤ 0.04) in CSPALM compared with CSMIX and CON. No treatment effects were detected (P ≥ 0.15) for plasma concentrations of glucose, insulin, insulin-like growth factor I, and leptin, nor for other LM genes associated with marbling and muscle growth. Concentrations of total fatty acids (FA) in plasma and LM steak samples were greater (P < 0.01) in CSMIX compared with CSPALM and CON, and greater (P < 0.01) in the LM samples of CSPALM compared with CON. Steers receiving CSMIX had greater (P < 0.01) concentrations of polyunsaturated and ω-6 FA in plasma and LM steak samples compared with CSPALM and CON. Supplementing CSMIX improved gain efficiency and FA profile in the LM of feedlot steers compared with the CON diet, but the same responses were not observed when CSPALM was offered. Perhaps the advantages from CSMIX supplementation resulted from increasing the supply of polyunsaturated and ω-6 FA to the finishing diet.