Evaluation of oregano leaves and plant bioactive lipid compounds as feed additives for growing rabbits: Effects on performance, nutrient digestibility, serum metabolic profile and carcass traits

This study evaluated oregano leaves and their plant bioactive lipid compounds (PBLC) as feed additives for fattening rabbits. A total of 200 30-day-old weanling California male rabbits (average body weight [BW] 543 +/- 15 g) were divided into two experimental groups and used in two separate experiments. Each experimental group included 100 animals which were assigned to five dietary treatments (n = 20 per treatment, each replicate consists of one animal) that included oregano leaves at concentrations of 0 (control group), 3, 6, 9, and 12 g/kg diet during the first experiment, whereas oregano PBLC concentrations during the second experiment were 0 (control), 46, 92, 138, and 184 mg/kg diet. The experiments lasted for 60 days. The PBLC concentration of oregano leaves was 15.3 g/kg and the dietary inclusion levels of PBLC were calculated to reflect their concentration in oregano leaves. Dietary oregano leaves and their PBLC improved BW, BW gain, and feed conversion ratio compared with the control group for both experiments. Furthermore, in other groups than the control group, the nutrient digestibility effectively responded to oregano leaves and their PBLC. Interestingly, faecal ammonia concentration, cholesterol blood concentration, urea and creatinine, enzyme activity of glutamic oxaloacetic transaminase, and glutamic pyruvic transaminase were decreased by supplemental oregano leaves and their PBLC to rabbits' diets compared with the control group. Oregano leaves and their PBLC improved the dressing percentages and decreased perirenal and scapular fat. Hence, our investigation demonstrates that oregano leaves and their PBLC can be used as an effective feed additve to improve growth performance, nutrient digestibility, carcass traits, and liver and kidney functions as well as reduce faecal ammonia concentration and serum cholesterol of growing rabbits. The best performance and health status were observed in growing rabbits that received oregano leaves at 9 g/kg and at oregano PBLC concentration of 138 mg/kg. The results suggest that oregano leaves can be included in growing rabbit diets at 9 g/kg without requiring the extra cost of PBLC extraction.

Automated summary

The study showed that oregano leaves and their PBLC can significantly improve the growth performance, nutrient digestibility, and organ functions of rabbits, while reducing fecal ammonia concentration and serum cholesterol levels.