Fatty acid and energy metabolism in broiler chickens fed diets containing either beef tallow or an oil blend.

The hypothesis tested was that the feeding of n-6 polyunsaturated fatty acids (PUFA) results in more whole-body fatty acid oxidation than the feeding of saturated fatty acids (SFA). It was reasoned that the increased fatty acid oxidation would be associated with enhanced whole-body energy expenditure and stimulated de novo fatty acid synthesis. To put the hypothesis to the test, broiler chickens were fed diets containing either beef tallow as source of SFA or an oil blend as source of n-6 PUFA. The broilers either had free access to their diet or were fed a restricted amount. Seven-day-old, male broiler chickens were used; they were kept individually in cages from 1 to 4 weeks of age. In the birds fed ad libitum, the n-6 PUFA diet reduced average daily feed intake (ADFI), but did not significantly affect average daily weight gain (ADG) and the feed:conversion ratio (FCR). The lower ADFI on the n-6 PUFA diet was associated with a higher apparent digestibility of total fatty acids. The ratio of deposition in the body to intake of digestible total PUFA, which reflected n-6 PUFA, was significantly decreased by the n-6 PUFA diet, pointing at preferentially increased n-6 PUFA oxidation on the n-6 PUFA diet. The ratio for n-9 monounsaturated fatty acids (MUFA) was higher than 1.0, which agrees with net de novo synthesis, but the n-6 PUFA diet induced a lower value than did the SFA diet. Feeding either the n-6 PUFA or SFA diet did not influence energy expenditure expressed as percentage of energy intake. This study supports the idea that dietary n-6 PUFA instead of SFA are preferentially oxidized, but no proof was obtained for enhanced energy expenditure and contrary to the hypothesis put forward, the n-6 PUFA diet depressed de-novo fatty acid synthesis.