Effects of dietary inclusion of natural zeolite and flaxseed on broiler chickens ’ body fat deposition in an extended fattening period

Zeolites occur in nature in specific kinds of rocks, mostly of volcanic origin (DONGARE and SABDE, 1996). They are composed of a negatively charged crystalline hydrated aluminosilicate framework, including alkali and alkaline earth counter cations along with small amounts of various other elements (MUMPTON and FISHMAN, 1977). Because of their threedimensional pore structure, zeolites are able to absorb and trap molecules of proper size, analogous to a sieve, as well as selectively release, specific molecules by ion exchange (SHURSON et al., 1984). Zeolites are either natural or synthetic in origin having quite different compositions and therefore different physical properties (ELLIOT and EDWARDS, 1991). Evidence in the literature suggests that there is a growth promoting effect when zeolites are used as additives in animal nutrition (SWEENY et al., 1979; HEMKEN et al., 1984; OLVER, 1997; POND, 1984; BERGERO et al., 1997; POULSEN and OKSBIERG, 1995; TSERVENI-GOUSI et al., 1995; YANNAKOPOULOS et al., 1995; TSERVENI-GOUSI et al., 1997; YANNAKOPOULOS et al., 2000; CHRISTAKI et al., 2001). It should be mentioned here that zeolites per se have no nutritive value and the minerals they contain are not digestible. The beneficial effects of their addition to animal rations should be ascribed to the facilitation of digestion by slowing the passage of the digesta through the digestive tract (EVANS and FARRELL, 1993; OLVER, 1997). Flaxseed or linseed (Linum usitatissimum L.) is grown in the Northern United States and Southern Canada, and it is cultured as a source of linseed oil. There are studies on the addition of flaxseed in broiler chickens diets and most of them are related to birds performance or to the effects on the fatty acid composition of the broiler meat (AJUYAH et al., 1991; LEE et al., 1991; ROTH-MAIER and KIRCHGESSNER, 1995; RODRIGUEZ et al., 2001; ALZUETA et al., 2003). Flaxseed is a potentially valuable source of energy, protein and αlinolenic acid (LNA). There is evidence that LNA (C18: 3, n-3) has beneficial effects on human health, and particularly in vascular disorders prevention (HARRIS, 1997), or in early neural development (UAUY et al., 1996). Hence, the need for increase in the LNA and the other unsaturated fatty acids in foods of animal origin for human consumption has been emphasized (DEPARTMENT OF HEALTH NUTRITIONAL ASPECTS, LONDON, 1994). By changing the fatty acid content in broilers’ diets, the fatty acid composition of the broiler meat produced can be modified (YAU et al., 1991; CRESPO and ESTEVE-GARCIA, 2001). However, there are still very few studies about the effects of dietary fat saturation on body fat deposition in broiler chickens, although the lipid deposition control is an issue matter of particular research interest in poultry meat production (FISHER, 1984; HERMIER, 1997). It has been shown that the incorporation of saturated fatty acids in broilers’ diets results in higher intramuscular and abdominal fat accumulation in comparison to the incorporation of unsaturated fatty acids (SANZ et al., 1999; CRESPO and ESTEVE-GARCIA, 2001). The objective of the present study was to investigate the effect of the dietary inclusion of natural zeolite (a clinoptiloliterich tuff) in combination to flaxseed (source of polyunsaturated fatty acids), on body fat deposition of broiler chickens in an extended fattening period.