In vitro and in vivo characterization of galactomannanes extracted from fenugreek seeds (Trigonella foenum-graecum) for young rabbit nutrition.

Abstract

This thesis tackles the possible characterisation and utilisation of fenugreek (Trigonella foenum-graecum) seed gum (FSG) in the nutrition of young rabbits during the post-weaning period as an alternative to antimicrobials uses. The study was focussed on the behaviour of the extracted gum with different dietary fibre levels, both in vitro and in vivo. In a first trial, starting from a basal commercial rabbit diet, three experimental diets were formulated with gradual levels of inclusion of FSG (0, 0.25, 0.50 %) given to three groups of rabbits starting from weaning to slaughter age. On the other hand, five experimental diets were formulated containing 0, 0.125, 0.25, 0.50 and 100% of FSG that were submitted to in vitro incubation with rabbit caecal inoculum during 72h. Gas production and fermentation traits were measured. Apparent faecal digestibility and caecal fermentation parameters were not significantly affected by the in vivo inclusion of FSG excep a slight decrease in the cecal pH. Gradual dietary inclusion of FSG increased in vitro concentration of volatile fatty acids (VFA), while pure FSG increased the asymptotic gas production. In vitro incubation of pure FSG decreased pH value, lactic acid concentration and N-NH3 concentration and increased that of VFA. In a second trial, FSG was characterised determining its chemical composition, galactose and mannose content and prebiotic potential. Pure FSG and gradual levels of FSG (0, 5, 10, 15 and 20 g/kg), included both in diets rich in soluble fibre (SF) from beet pulp (included at 10%) or in diets rich in insoluble fibre (IF) from defatted grape seeds (included at 10 %), were evaluated. They were submitted to enzymatic digestion with pepsin and pancreatin and then their indigestible fractions were submitted to fermentation using caecal inoculum. The indigestible fractions after enzymatic digestion were measured, as well as the nonfermentable fractions and the fermentation traits after incubation time (48 h). FSG was mostly composed of galactose and mannose (630 g/kg) in 1:1 ratio and a moderate protein level (223 g/kg). Pure FSG was weakly affected by enzymatic digestion, only 145 g/kg was dissolved. However, it was almost entirely disappeared (984 g/kg) during the fermentation process. Consequently, FSG increased VFA concentration and decreased both pH value and N-NH3 concentration. In a last third trial, four diets were formulated according to 2 x 2 factorial design: a conventional rabbit diet (C), the same C diet supplemented by 10 g/kg of FSG, a low-risk diet (LR), and the same LR diet supplemented by 10 g/kg of FSG. C and LR diets differed in SF and crude protein levels (CP). Two hundred and sixteen weaned rabbits (28 days of age) of the LP line were allocated in individual cages and divided randomly between the four treatments and allowed free access to feed and water. Mortality, morbidity, health risk index (HRi), daily feed intake (DFI), average daily gain (ADG) and feed conversion ratio (FCR) were controlled, Coefficient of total tract apparent digestibility (CTTAD) of nutrients and caecal environment were measured. FSG dietary inclusion at 10 g/kg did not affect performance or CTTAD of nutrients but did slightly increased neutral-detergent fibre (NDF) and acid detergent fibre (ADF) digestibility in C diets. Similarly, caecal parameters were not affected by FSG except caproic acid concentration in C diets. Nevertheless, LR diets decreased mortality, HRi, DFI, ADG and CTTAD of organic matter and CP but increased FCR and CTTAD of NDF and ADF respect to C diets. Moreover, LR diets increased VFA concentration, the proportion of acetic, isobutyric and isovaleric while decreased the dry matter of the caecal content, N-NH3 and the proportion of butyric, caproic and valeric acids. To summarise, FSG perfectly responds to the two first conditions to be prebiotic, being not digestible by gastrointestinal enzymes before the caecum and highly fermented once reached the caecum.