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The present work was performed to study the effect of dietary inclusion of different fatty acid combinations (saturated, n-3 and n-6 polyunsaturated fatty acids; PUFA) on caecal fermentation activity, feed intake, growth rate and feed efficiency of young rabbits around weaning (17 to 44 d) and fattening rabbits (28 to 63 d of age). Five diets were formulated using the same raw materials and including 3% of lard (A diet, rich in saturated fat), sunflower oil (S diet, rich in n-6 PUFA), linseed oil (L diet, rich in n-3 PUFA), sunflower oil and lard at 1:1 rate (SA diet), or linseed oil and lard at 1:1 rate (LA diet). In the first trial, the effect of the 5 diets on rabbit performance was evaluated in a fattening period from 28 to 63 d of age, with 490 rabbits allocated in individual cages; mortality rates were measured with 1670 rabbits (750 allocated in individual cages and 920 in collective cages, 8 rabbits/cage). In the second trial, 120 young rabbits were used from 17 to 44 d of age, weaned at 28 d, allocated in collective cages and randomly fed with A, S or L diets, evaluating performance and gut weight and caecum fermentation activity. The use of animal fat or vegetable oil and the richness in n-3 or n-6 PUFA of vegetable oils had no significant effect on the feed intake (130 g dry matter/d) and growth rate of fattening rabbits (45.5 g/d), but the inclusion of sunflower oil in diet improved feed conversion rate (2.79 for S diet vs. 2.87 for the rest of diets; P<0.01). Mortality rate was lower when vegetable oils were included in diet (34 and 37% for S and L diets respectively vs. 45% for A diet; P<0.05). Feed intake and growth rate increased quickly from 17 to 44 d, but only small occasional differences were recorded in growth rate of young rabbits, in favour of rabbits receiving animal fat from 17 to 21 d (P<0.05) or sunflower oil from 28 to 30 d (P<0.05). Caecal traits of rabbits at 30 and 44 d of age were similar for the different dietary groups, although butyric acid concentration in caecum content at 44 d was the lowest (P<0.05) with L diet.

ABSTRACT:The effects of the dietary inclusion of fats with different origin (lard or vegetal oil), fatty acid profi le (linseed or sunfl ower), oxidation level (fresh, peroxidised: 11 d at 55ºC or oxidised: 31 h at 140ºC) and vitamin E supplementation (0 or 100 ppm) on the rabbit diet apparent digestibility were studied. Digestibility coeffi cients of dry matter, organic matter, crude protein, ether extract and gross energy were determined in eight diets using 58 rabbits aged 49 d. Contrast analysis between groups of diets showed that lard, characterised by a greater saturated fatty acid content, compared with vegetal oils, rich in unsaturated fatty acid, reduced the apparent digestibility of ether extract (62.3 vs. 68.4%; P=0.0329). However, there were no signifi cant differences in the nutrient digestibility when linseed or sunfl ower oils (rich in ω-3 or in ω-6 polyunsaturated fatty acids, respectively) were compared. The oxidation degree of the sunfl ower oil and the supplementation with 100 ppm of vitamin E to the diets did not modify the apparent digestibility values of any dietary fraction.

The in vitro gas production technique was used to evaluate the fermentation kinetics of 125 whole citrus fruits samples (WCF). Six models were tested to describe the fermentation characteristics of this product characterized by high sugar and pectin and low protein content: 487, 195 and 64.7 g/ kg dry matter, respectively. The models were: exponential with and without lag (EXP 0 and EXP L , respectively); generalized Mitscherlich (GEXP L ); and one, dual and three pool logistic models (OLOG L, DLOG L and TLOG L , respectively). EXP 0 had the highest residual standard deviation (RSD=9.0 ml), the lowest being for the TLOG L (5.93 ml). TLOG L model obtained the best values fitting individual curves with a mean prediction error of 0.25 ml. Significant correlations were observed between the three different fractions of the TLOG L model and the chemical composition: quickly fermentable fraction with sugars (+0.43; P<0.001), high fermentable fraction with pectins (+0.23; P<0.05) and slow fermentable fraction with fibres (+0.38 and +0.34 for NDF and ADF, respectively; P<0.01), which could indicate the presence of three main fractions in WCF with different fermentation rates.