EFFECT OF OXIDATION STATE OF DIETARY SUNFLOWER OIL AND DIETARY ZINC AND α-TOCOPHERYL ACETATE SUPPLEMENTATION ON PERFORMANCE OF GROWING RABBITS

Twelve diets were formulated using the same raw materials and including 3% of sunflower oil at 3 different oxidation levels [fresh (F), peroxidised (P; 55 degrees C for 11 d; 83 meq O-2/kg oil) and highly-oxidised (O; 140 degrees C for 31 h; rho-anisidine value of 125)], with 2 levels of a-tocopherol supplementation (0 and 100 ppm), and 2 levels of Zn supplementation (0 and 200 ppm). A trial with 900 growing rabbits was carried out in order to study the effect of the oxidation and protection level of supplemented oil on the performance of animals from weaning (28 d) to 63 d of age. Another coetaneous trial was performed to study the effect of the oxidation level of sunflower oil (F, P and O) on caecal activity around weaning, using 120 suckling rabbits randomly re-allocated into 12 litters of 10 kits (4 litters per diet) from 17 to 44 d of age. Four rabbits per litter were slaughtered at 30 and 44 d (16 rabbits/treatment and age). Full gastro-intestinal tract and caecum were weighed and pH, dry matter (DM), ammonia nitrogen (NH3) and volatile fatty acids concentration (VFA) values in caecal content were measured. No effect was observed either in the mortality rate, body weight gain, feed intake or conversion rate throughout the growing period when peroxidised or oxidised oils were included in the diet, being on average 32%, 45.1 g/d, 107.6 g DM/d and 2.44, respectively. Dietary supplementation with a-tocopherol and/or Zn had no effect on the mortality rate, feed intake and performance of rabbits during the fattening period. Daily weight gain just after weaning (28 to 30 d of age) was higher for kits receiving the diet supplemented with F and O diets than those with the P diet (55, 50 and 35 g/d, respectively; P<0.05), but no further effect on performance was observed. Young rabbits fed with the P diet showed lower DM percentage in caecum at 30 d of age (-9.5%; P<0.05) than those with F or O diets. Caecum of young rabbits fed with the O diet presented lower NH3 content at 30 d of age that those given F diet (-38%; P<0.05) and higher total VFA and acetic acid concentration (+36 and +34 %, respectively; P<0.05). Therefore, and although many questions are still open, oxidised oils could be considered as a possible energy source for rabbit nutrition.