Alfalfa polysaccharides improve the growth performance and antioxidant status of heat-stressed rabbits

Abstract

The study was conducted to evaluate the antioxidant properties of alfalfa polysaccharides (APS) extracted from alfalfa ( Medicago sativa L.) through 1,1-Diphenyl-2-picryl-hydrazyl (DPPH) radical-scavenging assay and the effects of the inclusion (0%, 0.1%, and 0.5%) of APS in the diet on the growth performance and antioxidant status in heat-stressed rabbits. 120 New Zealand male rabbits (average body weight 1123 g, 40 d old) were divided into three groups (40 rabbits per group) and were fed with a basal diet or the basal diet with 1 g or 5 g of APS/kg of diet. Rabbits had free access to diets and water in an environmentally controlled room at 30 ± 1 °C and 55% relative humidity during the entire period (21 d). On days 7, 14 and 21 of the trial, body weight and feed intake were measured and blood samples were collected for assay of antioxidant induces. Liver tissue samples were collected on day 21 for assay of antioxidant induces. Results in vitro showed the scavenging effect of APS on DPPH radicals increased ( P < 0.05) in a dose-dependent manner. The APS exerted an inhibitory effect on DPPH radical generation, with 66.3% inhibition at 100 µg/mL and 74.5% inhibition at 250 µg/mL. Results in vivo showed that APS 0.1% supplementation increased ( P < 0.05) average daily gain (ADG) and reduced ( P < 0.05) feed conversion rate (FCR) in the first week of trial. Compared with the control group, average daily feed intake (ADFI) was significantly ( P < 0.01) reduced by APS treatment. From days 8 to 14 of the trial, ADG of the APS 0.5% group was greater ( P < 0.05) than that of the control group. Compared with the control group, FCR was significantly ( P < 0.05) reduced by APS treatment. From days 15 to 21 of the trial, ADFI of the APS 0.1% group was greater ( P < 0.05) than that of the control group. For the overall period, APS 0.5% supplementation had a significantly ( P < 0.05) positive effect on ADG. ADFI and FCR were lower ( P < 0.05) with APS than without APS. Furthermore, on day 7, the inclusion of APS reduced significantly MDA ( P < 0.01). The rabbits fed with APS 0.1% had significantly ( P < 0.01) lower cortisol and greater ( P < 0.05) T-AOC, SOD, and GSH-Px than the control group. On day 14, addition of APS increased T-AOC ( P < 0.01) and reduced MDA ( P < 0.05). The APS 0.5% group showed lower ( P < 0.05) cortisol and greater ( P < 0.05) GSH-Px than the control group. On day 21, the rabbits fed with the APS 0.5% diet had greater ( P < 0.05) GSH-Px and T-AOC compared with the control rabbits. In contrast, the opposite was true for cortisol ( P < 0.05) and MDA ( P < 0.05). On day 21, MDA was lower ( P < 0.01) with APS than without APS in the liver tissue. Hepatic GSH-Px activity of rabbits fed with the APS 0.5% diet was greater ( P < 0.05) than those of other groups. APS supplementation seemed to have a positive influence on the growth performance and antioxidant status of heat-stressed rabbits.