Two experiments were carried out to evaluate the inclusion of vegetable oils with different fatty acid content in starter and pre-starter broiler diets. In Experiment I 480 1-to 9-day-old male Ross 308 broilers were fed diets containing corn oil (CO), acid corn oil (ACO), linseed oil (LO) or coconut fat (CoF). Chicks were distributed according to a factorial 2x2x2arrangement (2 free fatty acids -FFA ) x (2 n6:n3 ratios) x (2 medium-chain fatty acids levels -AGMC). Performance responses and dry matter (DMM), crude protein (CPM), and crude fat (CFM) metabolizability were evaluated. In Experiment II, 480 1-to 20-day-old male Ross 308 broilers were offered the free choice of 2 different diets: with no fat addition, or with 10% addition of the following fat sources: CO, LO, CoF, soybean soapstock (SBS), acid soybean oil (ASO), or acid cottonseed oil (ACtO). Performance responses and diet selection were evaluated. In experiment I, there were no significant effects of the diets on performance, DMM, or CPM; however, the inclusion of FFA depressed CFM. In experiment II, there was a marked preference of birds of the diets with fat inclusion, leading to the selection of diets with more than 3100 kcal/kg ME in the period of 1 to 20 days, independently of fat source. The broilers selected the high fat and energy diets since the first days of age, which resulted in better bird performance.
INTRODUCTIONThe inclusion of fats in feeds positively influences broiler performance (Vieira et al., 2002;Pucci et al., 2003), and enhances feed palatability (NRC, 1994). The composition of the fatty acids added to diets affects body fat composition in broilers (Waldroup & Waldroup, 2005), and therefore body fat growth pattern can be modified by dietary fat (Crespo & Esteve-Garcia, 2002).Birds fed diets with high saturated fatty acids from animal origin deposit relatively more mesenteric and abdominal fat as compared to other sites of the body (Crespo & Esteve-Garcia, 2002). The increase in the proportion of saturated fatty acids in broiler diets causes weight gain depression and worse feed conversion ratio, as well as reductions in fat and fatty acids digestibility and energy metabolizability (Zollitsch et al., 1997;Dänicke et al., 2000). On the other hand, diets with high polyunsaturated fatty acid content promote lower body fat deposition (Crespo & Esteve-Garcia, 2002).The physiological capacity of birds during the first post-hatching days limits fat absorption (Carew et al., 1972), and the limited fat digestion seems to be caused by insufficient secretion of bile salts and lipase (Krogdahl et al., 1985). Fat digestibility in chicks is 6% lower than that of adult roosters (Freitas et al., 2005). In general, apparent fat metabolizability decreases as the proportion of dietary saturated fatty
