Use of olive pomace extracts in broiler chicken diets: effects on growth performance and gut health

Abstract

The need to find alternatives to the use of antibiotic growth promoters in poultry has led to an active research during the last years with the aim to develop different management and nutritional strategies to improve animal performance. In this context, feed additives such as phytochemicals are gaining interest as they promote growth and health because of their antioxidant, antimicrobial and anti-inflammatory effects. The positive properties of phytochemicals are related to certain components present in plants such as phenolic compounds, flavonoids or terpenoids. Olive oil from Olea europaea is an integral ingredient of the Mediterranean area with known health promoting effects. Bioactive compounds of olive fruit and olive oil include polyphenols (oleuropein and hydroxytyrosol) and triterpenes (oleanolic and maslinic acids) among others. Different extracts derived from olive mill wastes have shown positive effects on growth performance and intestinal health in food-producing animal species. However, the potential positive effects of bioactive extracts derived from olive oil industry in poultry are scarcely identified and remain to be investigated. The main objective of this Doctoral Thesis is to evaluate the effects of supplementing broiler chicken diets with a bioactive olive pomace extract from Olea europaea (OE) rich in polyphenols and triterpenes on animal growth performance and gut health. Three experiments were conducted with the following objectives: 1) study the effects of supplementing grower diets with OE on broiler performance and gut health; 2) evaluate the effects of supplementing starter and grower diets with the OE on performance and gut health after a challenge of intestinal permeability induced by a short-term fasting period; 3) investigate an experimental procedure of coccidial vaccine challenge in battery cages and the anticoccidial effect of the OE in broiler chickens. In trial 1 animals were fed with a standard non-medicated starter diet for 21 d, and from 22 to 42 d of age with their respective experimental diet: a negative control with no additives (Control), a positive control with 100 ppm of Monensin and the basal diet supplemented with 750 ppm of an OE (Lucta S.A., Spain) containing 2% of polyphenols and 10% of triterpenes. From 21 to 42 d of age, no significant differences in average daily feed intake (ADFI) were observed among dietary treatments; however, lower average daily gain (ADG) and higher feed conversion ratio (FCR) (P < 0.05) was observed in birds fed the Control compared to Monensin and OE groups. No significant changes on bacterial composition and diversity at a family level were observed in the caeca of birds fed the experimental diets. Moreover, no significant differences on plasma and intestinal bile acid composition were observed among treatments. Birds fed the OE showed a significant decrease of interleukin 8 (IL-8) expression in the ileum (P < 0.05). Additionally, the expression of transforming growth factor beta 4 (TGF-β4), and chicken B-cell marker (Bu-1) was significantly upregulated (P < 0.01) in broilers fed the OE and Monensin diets compared to those fed the Control. In conclusion, the inclusion of 750 ppm of the OE improved animal growth likely as result of its anti-inflammatory properties. In trial 2, treatments included a control diet with no additives (CF), and diets supplemented with 100 ppm of monensin (MF) or with 500 (OE500F) or 1500 ppm (OE1500F) of an OE (Lucta S.A., Spain) containing 1% of polyphenols and 6% of triterpenes. At 14 d, all birds were submitted to a 15.5 h short-term fasting period to induce intestinal permeability (IP) increase. In addition, a control group was included, fed the control diet and no challenged with the fasting period (CNF). No significant differences were observed in ADG, ADFI and FCR among treatments before fasting period (from 1 to 14 d of age). Fasting increased (P < 0.05) lactulose/mannitol ratio and Alpha 1 Acid Glycoprotein concentration in plasma and reduced (P < 0.001) duodenum villus/crypt ratio (VH/CD). Moreover, a down-regulation of Claudin-1 (P < 0.05), an up-regulation of toll-like receptor 4 (TLR4) and IL-8 (P < 0.05) ileal gene expression was observed in CF birds compared to CNF. The OE500F treatment reduced duodenal crypt depth compared to CF (P < 0.05; OE linear effect). Mannitol concentration and ileal IL-8 expression were reduced in OE500F compared to CF and OE1500F (P = 0.05). Fasting challenge induced an increase in IP triggering an inflammatory response. Supplementation of OE up to 1500 ppm did not affect growth performance in birds fed the extract up to 32 days of age but alleviated some of the negative effects of the fasting challenge. In trial 3, broiler chickens were randomly assigned to 5 experimental treatments. One group was fed the control diet without any additives and no challenged (NCU). The other 4 groups were challenged and fed the control diet with no additives (NCC), or supplemented with 500 ppm of coccidiostat (PCC) or with 500 (OE500C) and 1500 ppm (OE1500C) of OE (Lucta S.A., Spain) containing 1% of polyphenols and 6% of triterpenes. At 0, 7 and 14 d, all birds, except NCU group, were challenged with an oral gavage of a live Eimeria spp oocyst vaccine at 1x, 4x, and 16x of the manufacturer’s recommended dose, respectively. Coccidial vaccine challenge depressed body weight (P < 0.05) throughout the trial, as well as a reduction (P < 0.05) of FI and BWG except from 20 to 28 d, and FCR from 0 to 7, 0 to 14 and 0 to 20 d. Birds in the NCC group had higher (P < 0.05) oocyst counts and lower (P < 0.05) carotenoid plasma concentration and VH/CD ratio in duodenum and jejunum compared with NCU birds. Overall, coccidia challenge caused the expected reductions in growth performance and gut integrity. While the coccidiostat reduced oocysts excretion, dietary OE or coccidiostat had no effects on performance or gut integrity. The attenuated inflammatory response observed for all the treatments following the third infection can be attributed to the adaptation or immunization to the repetitive exposure to Eimeria spp. In summary: a) Feeding broiler diets supplemented with an olive pomace extract under standard conditions did not affect performance up to 32 days of age. However, in the grower-finisher phase (from 35 to 42 days of age) the addition of 750 ppm of the extract providing 15 ppm polyphenols and 75 ppm triterpenes improved ADG and FCR.; b) The positive effects of the olive pomace extract on animal growth might be related to the anti-inflammatory properties of the olive triterpenoids and polyphenols reflected by the immunosuppressant effect on IL-8 pro-inflammatory interleukin and the increase of anti-inflammatory expression of TGF-β4; c) A single short-term fasting period of 15.5 h in birds housed in floor pens induced an increase in intestinal permeability triggering an inflammatory response; d) The addition of 500 ppm of the olive pomace extract providing 5 ppm polyphenols and 30 ppm triterpenes alleviated some of the negative effects of increased permeability associated with the short-term fasting challenge.; e) The experimental model of coccidial vaccine challenge used induced growth depression and gut integrity reduction as indicated by increased oocyst excretion, reduced plasma carotenoid concentration, and intestinal morphology alteration.; f) Under the experimental coccidiosis challenge, the inclusion of 500 ppm or 1500 ppm of the olive pomace extract providing up to 15 ppm of polyphenols and 90 ppm of triterpenes showed no effects on performance or gut integrity. This suggests that the potential anticoccidial effects of olive pomace extracts depend on the concentration and type of the bioactive compounds and/or the Eimeria strain.