Effects of conjugated linoleic acid (CLA) on growth and carcass characteristics when fed for differing amounts of time and when fed with high oil corn (HOC) to growing-finishing swine
Two experiments were conducted to determine the effects of CLA on growth, carcass quality and pork quality. In the first experiment, 92 four-way cross barrows were fed 0.75% CLA for differing periods of weight gain. ADG and ADFI were not affected by feeding CLA. Gain:feed ratio over the entire experiment increased quadratically (P < 0.05) in response to length of feeding CLA. Backfat (BF) depth decreased linearly (P < 0.05) and loin muscle area (LMA) decreased linearly (P < 0.01) in response to increased days of feeding CLA. However, there were also strong trends for quadratic responses for BF and LMA. These quadratic responses were indicative of diminishing effects as period of feeding CLA lengthened. Marbling (P < 0.03) and firmness (P < 0.07) scores increased linearly with increased length of CLA feeding. In summary, all responses to CLA were near maximum if fed for the last 58 kg of BW gain before slaughter. In the second experiment 48 PIC barrows were fed diets containing normal corn (NC), NC and CLA (NC+CLA ), high oil corn (HOC), HOC and CLA (HOC+CLA), NC and choice white grease (CWG) (NC+CWG) or NC, CWG and CLA (NC+CWG+CLA). NC and NC+CLA diets (low energy, LE) contained 3.3 Mcal ME/kg, whereas all other diets (high energy, HE) contained 3.5 Mcal ME/kg. For the first 42 d, pigs fed HE had greater (P < 0.05) gain/feed (GF) than pigs fed LE. For the overall trial there was no difference in GF between pigs fed diets containing HOC and pigs fed LE. However, pigs fed diets containing CWG did have a greater (P < 0.05) GF than pigs fed diets containing HOC. For the overall trial, pigs fed CLA had reduced (P < 0.05) GF. Carcasses of pigs fed LE diets had less (P < 0.04) BF than those of pigs fed HE. Bellies from pigs fed CLA were firmer (P < 0.001) than bellies from those fed other treatments. Bellies of pigs fed the HOC diets were softer (P < 0.03) compared with bellies of pigs fed the NC diets, but the pigs fed HOC+CLA had bellies that were slightly firmer (P < 0.13) than those from pigs fed NC diet but less (P < 0.03) firm than those from pigs fed NC+CLA. In summary, CLA increased belly firmness, correcting the negative effect caused by feeding a high level of polyunsaturated fatty acids that is found in HOC, but did not improve growth performance.