Nutritive value of dehydrated sainfoin (Onobrychis viciifoliae) for growing rabbits, according to the harvesting stage

In rabbit production, the use of dehydrated sainfoin, a Legume containing phenols and condensed tannins (CT), has received recent attention because of its nutraceutical properties. Here, we aimed to compare the nutritive value of dehydrated Perly cultivar sainfoin for a first cut (SC1: crude protein = 200 g/kg, Acid detergent fiber (ADFom) = 208 g/kg, CT = 11.8 g/kg), or a third cut (SC3: crude protein = 159 g/kg, ADFom = 228 g/kg, CT = 17.5 g/kg). The digestibility of two sets of 4 diets, made either with SC1 or with SC3, and containing either 0, 120, 240, or 360 g/kg of dehydrated sainfoin (DS0, DS120, DS240, DS360) in dilution with a basal mixture was compared based on a regression statistical procedure. A direct measure of the nutritive value of SC1 was performed with a supplemental diet containing 980 g/kg (DS980) of SC1. In trial 1, four groups of 12 growing rabbits received SC3 diets. In the trial 2, five groups of 8–9 rabbits received SC1 diets. Rabbits were allotted at weaning (35 days), housed individually in metabolism cages and fed ad libitum during six weeks. Sainfoin digestibility was measured for both trials in 6 weeks old rabbit, and in 8 weeks old rabbit only for trial 2. The digestibility of energy and particularly that of protein linearly decreased with the increase in SC3 incorporation in diets (P < 0.001). Using a regression procedure, SC3 digestible energy (DE) and protein (DP) concentrations were respectively 6.70 ± 0.15 MJ DE/kg and 53 ± 4 g DP/kg as fed, corresponding respectively to a 40 % and 33 % digestibility coefficient. On the contrary energy digestibility was relatively stable from 0 to 360 g/kg SC1 incorporation in diets, in both 6 wks. and 8 wks. old rabbits whereas the digestibility of protein decreased linearly with SC1 incorporation in diets (P < 0.001) as observed with SC3 incorporation. SC1 DE and DP concentration were respectively 8.84 ± 0.25 MJ DE/kg, corresponding to an energy digestibility of 58 %, and 79 ± 5 g DP/kg corresponding to a protein digestibility coefficient of 40 %. Nitrogen retention coefficients slightly decreased with SC3 incorporation. With SC1 incorporation, nitrogen retention coefficients were stable. With SC3 incorporation level the protein digestibility decreased sharper (P < 0.05) than for SC1. The DE content of SC1 calculated by regression gave similar results than a direct measurement (DS980), while the DP content was lower by regression compared to the direct measure (74 vs 92 g/kg). Thus for future assays of sainfoin nutritive value the use of a direct measure could be recommended for DE estimation.