Citrus aurantium flavonoid extract improves concentrate efficiency, animal behavior, and reduces rumen inflammation of Holstein bulls fed high-concentrate diets

One hundred fourty-four bulls (164.8 ± 5.91 kg BW and 135 ± 7.2 d of age) were randomly allocated to one of 8 pens and assigned to control (C) or citrus flavonoid (BF) treatments (Citrus aurantium, 0.4 kg per ton of concentrate of Bioflavex CA, > 20% naringin; BF). Each pen had one drinker, one separate five-space straw feeder, and one separate three-space feeder where mash concentrate containing mostly corn, barley, DDG and wheat was offered. Concentrate intake was recorded daily, whilst BW and animal behavior were recorded fortnightly. Animals were slaughtered after 168 d of study (12 periods of 14 d), and HCW and carcass quality were recorded, and rumen papillae samples were collected. Final BW (437.9 ± 1.85 kg), HCW (238.7 ± 2.02 kg), and concentrate intake (7.1 ± 0.13 kg/d) were not affected by treatment. Concentrate feed conversion ratio (kg of concentrate/ kg of BW) tended (P < 0.10) to be lesser in BF than in C bulls (5.11 vs. 5.36 ± 0.108 kg/kg). Percentage of animals eating concentrate during visual scan was greater (P < 0.01) in BF compared with C bulls (10.02 % vs. 7.97 % ± 0.512). Oral non-nutritive behaviors, agonistic interactions (fighting, butting, and chasing) and sexual behaviors (flehmen, attempted and complete mounts) were greater (P < 0.01) in C than in BF bulls. In the rumen epithelium, gene expression of bitter taste receptor 7, bitter taste receptor 16, bitter taste receptor 38 and bitter taste receptor 39 was greater (P < 0.05) in C compared with BF bulls, as well as was gene expression of free fatty acid receptor 2, pancreatic polypeptide receptor 1, cholecystokinin receptor 4, cytokine IL-25, Toll-like receptor-4 and β-defensin1. In conclusion, supplementation with flavonoids extracted from Citrus aurantium in bulls fed high-concentrate diets tends to improve efficiency, and reduces oral non-nutritive behaviors, agonistic interactions and sexual behavior. Moreover, flavonoid supplementation modifies the expression of genes in the rumen epithelium that could be related with eating and animal behavior regulation.