The effect of dietary fat on the performance, carcass quality, fatty acid composition and storage stability of turkeys
Salmon, Raymond Edward
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The effect of the level and source of dietary fat on the performance of growing turkeys and on the finish, meat yield, composition and storage stability of the carcass was studied. Male turkeys were fed, from day-old to 24 weeks of age, diets of equal calorie: protein ratio containing either rapeseed or palm oil at either 2 or 11.4% of the diet, in comparison with a control diet which contained no added fat. Treatments were included in which the dietary fat was changed at 16 weeks from palm to rapeseed oil or vice versa, to permit observation of the effect of a change of the fat source on carcass composition and of the rate of change of carcass fatty acid composition following a change of dietary fat. Body growth was found to be depressed by 11.4% rapeseed oil but stimulated by 11.4% palm oil. Feed conversion was inversely proportional to the level of added fat. Increasing the dietary fat level improved carcass fat scores, increased the yield of skin, the fat content of breast and thigh meat and drip losses in cooking, and decreased the yield of breast meat, thigh meat and drumstick and volatile cooking losses. The initial addition of 2% fat to the diet had more effect on the carcass characteristics than a further increase from 2 to 11.4% fat. Volatile cooking losses decreased and drip losses increased with increasing carcass skin percentage. The source of dietary fat influenced the carcass fat score, carcass composition and cooking losses. Back fat score and back skin fat were more reliable indicators of overall finish as measured by carcass skin percentage than breast fat score and breast skin fat. The fatty acids of abdominal depot fat and thigh and breast meat were strongly influenced by the level and source of dietary fat. Birds fed no added dietary fat deposited palmitic, palmitoleic, stearic and oleic acids in greater proportions than were provided in the diet. Increasing the level of fat in the diet resulted in the deposition of fat that resembled the dietary fat in composition, the greatest similarity occurring at the higher level of added fat. Increasing levels of palmitoleic, stearic and oleic acids with age indicated that the rate of fatty acid biosynthesis increased as the birds approached maturity. Thigh meat contained a higher level of stearic acid than depot fat, and breast meat contained higher levels of stearic and arachidonic acids and fatty aldehydes than thigh meat. These differences reflected the greater proportions of phospholipids in thigh and breast meat, which were reflected also in decreased sensitivity of the meat lipids to changes in fatty acid composition in response to dietary fat. The average rate of change of fatty acid levels following a change of dietary fat at 16 weeks was such that half the total change in level took place in 2.4 weeks. Carcasses of birds fed 11.4% rapeseed oil were subject to rancidity, as measured by TBA value, when stored for eight months at a temperature of -12°C, but not when stored at -22°C. Carcasses of birds fed 11.4% palm oil were equally stable at both storage temperatures. The instability associated with dietary rapeseed oil was related to higher levels of linoleic and linolenic acids in the tissues as compared with those of birds fed palm oil.