Effect of quercetin supplementation on the growth, feed efficiency and serum hormone levels of New Zealand White rabbits

Meat rabbits could provide a new avenue for agricultural development in South Africa, and flavonoids may be able to improve their live performance. This study investigated the effects of quercetin dihydrate (0 and 2 g/kg feed) on the growth parameters and serum-free triiodothyronine (fT3), free thyroxine, somatotropin, and cortisol levels of growing rabbits. It also provides the first growth and feed conversion ratio (FCR) data for South African New Zealand Whites. Control (Ctrl) and quercetin-supplemented (Qrc) diets were provided to 34 (16 male, 18 female) and 32 (15 male, 17 female) rabbits, respectively, from 5 to 12 weeks old. Live performance was measured weekly, and serum hormone levels were determined at 11 weeks old. Overall, the rabbits performed well for live weight and growth rate, growing from 1052 ± 13.4 g to 3192 ± 45.3 g (5 - 12 weeks). Females had higher cortisol levels than males, as found for other species (female = 10.9 ng/mL, male = 3.89 ng/mL). Qrc rabbits tended to have a higher overall FCR than Ctrl rabbits (Ctrl = 3.83, Qrc = 4.01), possibly due to lower feed digestibility, and had smaller sex differences in growth and FCR than Ctrl rabbits, possibly owing to xenoestrogenic activity. They also tended to have higher fT3 levels than Ctrl rabbits (Ctrl = 3.62 ng/mL, Qrc = 4.98 ng/mL), possibly owing to the inhibition of binding to transthyretin. However, it does not seem that the provision of quercetin is commercially justified for improving the live performance of rabbits.Keywords: Cortisol, feed conversion ratio, flavonoid, growth, rabbit, somatotropin, thyroid hormone