BACKGROUND
Bovine colostrum (BC) is the first mammary secretion after birth and contains macronutrients, micronutrients, and bioactive compounds with reported antioxidant properties. It includes enzymatic antioxidants such as catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx), as well as non-enzymatic antioxidants such as vitamins E, A, and C, lactoferrin, and selenium. Because rabbit meat contains a high proportion of poly-unsaturated fatty acids, the authors considered antioxidant nutrition potentially relevant for rabbit production. Prior studies in piglets and calves suggested beneficial antioxidant effects of BC, but the authors stated that no studies had evaluated its effects on antioxidant status in rabbits. The aim of this study was therefore to test whether dietary BC supplementation at 2.5% or 5.0% alters plasma antioxidant enzyme activity and tissue gene expression of antioxidant enzymes in rabbits.
METHODS
The investigators studied 30 post-weaning New Zealand White male rabbits aged 37 days with an average body weight of 550 ± 24 g. Rabbits were randomly assigned to 3 diets: a control diet without BC (CON), the control diet plus 2.5% liquid bovine colostrum (BC-2.5), or the control diet plus 5.0% liquid bovine colostrum (BC-5). The colostrum was collected from multiparous Holstein–Friesian cows during the first milking and was classified as high quality at >23% Brix. Rabbits were fed ad libitum with free access to water and kept under the same management, hygienic, and environmental conditions. After 37 days of feeding, the animals were slaughtered at a body weight of 1977 ± 26 g. Fasting blood was collected, and liver and longissimus dorsi (LD) muscle samples were harvested for molecular analyses.
The antioxidant characteristics of BC and the diets were measured before biologic testing. Total phenol content (TPC) was measured by the Folin-Ciocalteu method. Antioxidant activity was assessed by DPPH, ABTS, and ORAC assays and expressed as Trolox equivalent antioxidant capacity. Plasma CAT, GPx, and SOD activities were measured using commercial Cayman Chemical assay kits. For tissue analyses, total RNA was extracted from liver and LD samples, converted to cDNA, and analyzed by real-time quantitative PCR. The target genes were CAT, GPx, and SOD, with GAPDH and ACTB as reference genes. Relative gene expression was calculated using the 2^−ΔΔCt method. Statistical analysis was performed in SPSS 26.0. Data were expressed as means ± SD, normality was assessed with the Kolmogorov–Smirnov test, and treatment and tissue effects were analyzed by ANOVA, with significance set at p < 0.05.
KEY RESULTS
The BC itself had a TPC of 0.084 ± 0.005 mg GAE/mL. Its antioxidant activity values were 0.34 ± 0.05 μmol/TE by DPPH, 2.00 ± 0.13 μmol/TE by ABTS, and 3.92 ± 0.19 μmol/TE by ORAC. In the diets, TPC did not differ significantly: 3.85 ± 0.15 mg GAE/g in CON, 4.09 ± 0.27 mg GAE/g in BC-2.5, and 3.84 ± 0.08 mg GAE/g in BC-5. DPPH also did not differ significantly: 11.13 ± 0.20, 11.14 ± 0.19, and 11.16 ± 0.17 μmol TE/g, respectively. ABTS was likewise not significantly different at 36.42 ± 1.84, 34.88 ± 0.23, and 36.12 ± 0.42 μmol TE/g. In contrast, ORAC increased across diets and was significantly different: 113.00 ± 3.8 μmol TE/g in CON, 136.3 ± 4.5 μmol TE/g in BC-2.5, and 150.70 ± 5.8 μmol TE/g in BC-5, with p < 0.001.
Despite this higher measured antioxidant capacity in the diets, plasma antioxidant enzyme activities were not significantly altered by supplementation. Plasma CAT was 11.68 ± 1.86 U/mL in CON, 9.82 ± 1.75 U/mL in BC-2.5, and 7.66 ± 2.11 U/mL in BC-5, with p = 0.347. Plasma GPx was 196.21 ± 16.67 U/mL, 253.46 ± 33.39 U/mL, and 237.27 ± 21.85 U/mL, with p = 0.265. Plasma SOD was 91.72 ± 8.69 U/L, 87.38 ± 7.83 U/L, and 77.82 ± 6.85 U/L, with p = 0.449.
Gene expression analyses in liver and LD muscle also showed no significant diet-related effects. For CAT, liver expression was 2.067 ± 0.79 in CON, 1.995 ± 0.56 in BC-2.5, and 1.786 ± 0.35 in BC-5, while LD values were 1.568 ± 1.08, 2.659 ± 1.28, and 2.459 ± 1.18; the diet effect was p = 0.237 and the tissue effect was p = 0.257. For GPx, liver expression was 1.439 ± 0.72, 1.244 ± 0.61, and 0.997 ± 0.24, while LD expression was 0.739 ± 0.31, 0.806 ± 0.35, and 0.886 ± 0.31; the diet effect was p = 0.606, but the tissue effect was significant at p = 0.001. For SOD, liver expression was 1.384 ± 1.25, 0.722 ± 0.15, and 0.657 ± 0.15, while LD expression was 1.086 ± 0.40, 1.315 ± 0.44, and 1.449 ± 0.37; the diet effect was p = 0.471 and the tissue effect was significant at p = 0.022. The authors summarized this as a significant tissue-related effect, with SOD mRNA levels higher in LD and GPx mRNA levels higher in liver.
CLINICAL IMPLICATIONS
Under the conditions tested, dietary BC supplementation at 2.5% and 5.0% did not improve systemic antioxidant enzyme activity or induce significant diet-related changes in hepatic or muscle antioxidant gene expression in healthy rabbits. The study suggests that a measurable increase in feed antioxidant capacity, particularly by ORAC, does not necessarily produce detectable in vivo antioxidant effects in the absence of oxidative stress. For rabbit farming and veterinary nutrition, the practical implication is that BC at these doses and for 37 days may not be sufficient to enhance antioxidant defenses in healthy post-weaning rabbits. The authors propose that lack of stress exposure, limited bioavailability after digestion and biotransformation, or insufficient dose or duration may explain the null findings. They conclude that future studies should examine higher doses, longer supplementation periods, or combinations with synergistic factors to better define whether BC has useful nutraceutical value in rabbits.