|dc.description.abstract||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 -12Â°C, but not when stored
at -22Â°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.||en_US