| Five experiments were designed to study the effects of dietary incorporation of medium-chain triglyceride as a replacement for soybean oil on performance, carcass composition, meat quality, serum lipids and gene expression of key enzymes and transcription factors in male broilers. In Exp.1, a total of540, one-day-old, male Arbor Acres broilers were randomly allotted to1of5treatments with each treatment being applied to6replicates of18chicks. The basal diet (i.e.,100:0) was based on corn and soybean meal and was supplemented with1.5%soybean oil during the starter phase (d0to21) and3.0%soybean oil during the grower phase (d22to42). Four experimental diets were formulated by replacing25,50,75or100%of the soybean oil with coconut oil (i.e.,75:25,50:50,25:75, and0:100). The feeding trial showed that dietary coconut oil had no effect on weight gain, feed intake or feed conversion. On d42, serum levels of total cholesterol, low-density lipoprotein cholesterol, and low-density lipoprotein/high-density lipoprotein cholesterol were linearly decreased as the coconut oil level increased (P<0.05). Lipoprotein lipase, hepatic lipase, and total lipase activities were linearly increased as the coconut oil level increased (P<0.05). Abdominal fat weight/eviscerated weight, intermuscular fat width and subcutaneous fat thickness showed a significant quadratic relationship, with the lowest value at25:75(P≤0.05). Exp.2investigated the effects of dietary incorporation of coconut oil as a replacement for soybean oil on meat appearance, fatty acid composition and oxidative stability. The treatments design was the same with Exp.1. An increase in the inclusion of coconut oil produced a linear increase in yellowness, lauric (C12:0) and myristic (C14:0) acid content, and a linear decrease in pH, redness, drip loss, linoleic acid (C18:2n-6), n-6to n-3ratio and malondialdehyde production in breast muscle. Exp.3was conducted to investigate the effects of dietary coconut oil on hepatic transcription and gene expression in liver, abdominal fat and breast muscle related to lipid metabolism and meat quality in male broilers. The treatments design was the same with Exp.1. The liver adiponectin gene expression was linearly increased, and SREBP-I and FAS gene expression were linearly decreased as the coconut oil level increased (P<0.05). In abdominal fat, the adiponectin gene expression was linearly increased (P=0.05). CPT-I expression in100:0was significantly lower than in50:50,25:75and0:100treatments (P=0.03). In Exp.4, a total of540, one-day-old, male Arbor Acres broilers were randomly allotted to1of5treatments with each treatment being applied to6replicates of18chicks. The basal diet (i.e.,100:0) was based on corn and soybean meal and was supplemented with1.5%soybean oil during the starter phase (d0to21) and3.0%soybean oil during the grower phase (d22to42). Four experimental diets were formulated by replacing25,50,75or100%of the soybean oil with octyl and decyl glycerate (i.e.,75:25,50:50,25:75, and0:100). The feeding trial showed that the ADFI in25:75and0:100treatments were significantly lower than the other3treatments (P<0.02) while the feed/gain ratio was not affected. Abdominal fat content, abdominal weight/eviscerated weight, intermuscular fat width, pH, redness, yellowness, drip loss, linoleic acid (C18:2n-6) and PUFA to SFA ratio were linearly decreased in breast muscle (P<0.05). On d42, serum levels of total cholesterol changed quadratically with the lowest level in50:50treatment (P=0.04). Triglyceride increased from 25:75treatment (P=0.02). Lipoprotein lipase, hepatic lipase, total lipase activities and leptin changed quadratically with the lowest level in50:50treatment (P<0.05). Exp.5was conducted to investigate the effects of dietary octyl and decyl glycerate on hepatic transcription and gene expression in liver and abdominal fat related to lipid metabolism and meat quality in male broilers. The treatments design was the same with Exp.4. The liver ACC gene expression was linearly decreased (P<0.05). In abdominal fat, PPARy gene expression was linearly increased (P<0.05), adiponectin gene expression was not significantly different (P>0.05). These results demonstrated that both replacement of75%of the soybean oil in diets with coconut oil and replacement of50%of the soybean oil in diets with octyl and decyl glycerate could reduce fat deposition, favorably affect lipid profiles and improve meat quality without impairing performance in broilers, and influence the lipid metabolism by regulating the transcription factors, hepatic lipogenic gene and fatty acids oxidation gene expression. |
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