The hypothesis of this experiment was that a liquid rich in hydroxytyrosol (HT) obtained from “alperujo”, an olive oil by-product, could replace part of the added vitamin E (VE) as an antioxidant in poultry diets. There were five diets that differed exclusively in the substitution of supplemental VE (0 to 40 mg/kg, with differences of 10 mg/kg) by HT (30 to 0 mg/kg, with differences of 7.5 mg/kg). The basal diet was based on corn and soybean meal and provided 10 mg VE/kg. From 0 to 39 d of age, the growth performance of the birds was not affected by diet. The birds were slaughtered at 39 d of age to evaluate the quality of the breast, and malonaldehyde concentration, pH, color, and drip loss were measured. In terms of meat lipid oxidation, the combination of 22.5 mg HT/kg and 10 mg of added VE/kg equalized to a diet supplemented with 40 mg VE/kg. Meat color improved in broilers fed 7.5 mg HT/kg and 30 mg VE/kg. It is concluded that once the nutritional requirements of the birds in VE are satisfied, the dietary supplementation with the olive oil by-product rich in HT can be used as a strategy to spare VE in broiler diets.

This research aimed to evaluate the effects of an olive pomace extract (OE) and a fat-encapsulated extract composed of a blend of oleoresins from Capsicum sp., black pepper, and ginger (SPICY) on broiler chicken performance and antioxidant function. In total, 640 1-day-old male chicks were randomly assigned to five experimental diets (eight replicates/treatment, 16 birds/replicate). Diets included a basal diet with no added vitamin E (NC), NC plus 100 ppm of vitamin E (PC), NC plus 1250 ppm of OE, NC plus 250 ppm of (SPICY), and NC plus 1250 ppm OE plus 250 ppm of SPICY (SPIOE). Phytogenic additives were supplied by Lucta S.A., Spain. Compared to the NC, the PC significantly (p < 0.05) increased ADG from 8 to 14 days of age, with both OE and SPICY showing intermediate values between both controls. At the end of this trial, at 35 days of age, a significant (p < 0.05) increase in plasma GPx activity was observed in PC-fed birds compared to the NC, with no effects of malonyl dialdehyde (MDA) and total antioxidant capacity. Birds fed the OE and SPICY displayed intermediate values of GPx activity compared to both controls. The expression of heat shock protein 70 (HSP70) and glutathione S-Transferase Alpha 4 (GSTA4) was significantly lower (p < 0.05) in the jejunal mucosa of birds fed the OE compared to the NC. Moreover, the expression of HSP70 was significantly lower (p < 0.05) in birds fed the OE compared to SPICY but was not significantly different compared to the blend of both extracts (SPIOE). In conclusion, OE and SPICY were useful in maintaining growth performance in no vit E-supplemented diets, particularly in the case of OE mediated by its antioxidant action through HSP70.

The study examines the effect of replacing vitamin E (VE) with a liquid obtained from alpeorujo, an olive oil by-product rich in hydroxytyrosol (HT), as an antioxidant in broiler chicken feeds on the gene expression, lipid profile, and oxidation in the liver. There were five diets that differed only in the substitution of supplemental VE (0 to 40 mg/kg with differences of 10 mg/kg) by HT (30 to 0 mg/kg with differences of 7.5 mg/kg). A linear decrease (p < 0.05) in α-tocopherol concentration in the liver was observed with the replacement of VE by HT. There were no significant changes in triglyceride, cholesterol, or TBARS concentrations. The hepatic transcriptome showed 378 differentially expressed genes between broilers fed HT15 (20 mg/kg VE and 15 mg/kg HT) and HT0 (40 mg/kg VE) diets (p < 0.05 and fold change less or higher than 1.3). Significant changes in cell cycle, cell nucleus activity, neuroactivity, and necroptosis pathways and functions were observed. It is concluded that the olive oil by-product, rich in HT, could be used to spare VE as an antioxidant in broiler diets without affecting liver lipid and TBARS concentrations. The differential gene expression analysis showed a potential role of olive polyphenols in enhancing the chicken immune response.

The aim of this study was to test the in vivo antioxidant capacity in broilers of two phytogenic additives, one derived from olive pomace (OE) and an encapsulated product based on Capsicum sp., black pepper, and ginger (SPICY), in a challenge using oxidized lipids in the feed. A total of 720 one-day-old male Cobb 500 were allocated to 72 pens (8 treatments, 9 replicates, 10 birds/replicate). The treatments were arranged in a 2 × 2 × 2 factorial, the factors being: fat source (4% soybean oil or 4% peroxidized soybean oil); SPICY (0 or 250 ppm); and OE (0 or 3077 ppm). From 1 to 21 days (global period) no significant differences were observed on performance. Broilers fed peroxidized oil showed higher plasma ferric reducing antioxidant power (FRAP; P < 0.05) values and higher catalase (CAT) activity compared to those fed fresh oil except in those birds fed the OE which remained constant with both oil sources (P < 0.05 for the interaction). Broilers fed OE showed a significant lower CAT gene expression in the liver (P < 0.05). Moreover, the heat shock protein 70 (HSP70) gene expression was lower in birds fed fresh oil and OE compared to those fed fresh oil without OE but higher in birds fed peroxidized oil and OE compared to those fed peroxidized oil without OE (P < 0.05 for the interaction). By contrast, broilers fed SPICY upregulated CAT (P < 0.05) and downregulated HSP70 (P < 0.05) gene expression in the liver compared to those not supplemented with SPICY. In conclusion, feeding broilers with peroxidized soybean oil from 1 to 21 days of age did not affect the productive parameters. However, the presence of lipid peroxidation products in the feed triggered both non-enzymatic and enzymatic antioxidant responses to maintain the oxidant/antioxidant balance. In the case of birds fed the OE, the enzymatic antioxidant response was more attenuated, indicating a better control of oxidative stress, likely mediated by HSP70.

During their productive cycle, broiler chickens are exposed to multiple stressors that can increase reactive oxygen species production, causing an imbalance between prooxidant systems and endogenous antioxidants. This imbalance leads to oxidative stress, which negatively affects health, growth and immune function, increasing susceptibility to infectious and pathological processes. To counteract lipid peroxidation and other oxidative damages, synthetic antioxidants are added to the diet, with vitamin E ( tocopherol) as the reference compound due to its strong radical stabilizing capacity and protection of biological membranes. However, the high cost and price variability of synthetic vitamin E, together with the need for more sustainable poultry production, have encouraged the search for alternative antioxidants. Phytogenic feed additives (PFAs), rich in bioactive compounds, can improve antioxidant status, support immunity, act as biocides or enhance digestibility. Many PFAs also originate from agri food byproducts, contributing to circular economy strategies. Their use has therefore increased in recent years, although further research is needed to clarify their mechanisms of action and potential synergies with common additives such as vitamin E. This thesis addresses these aspects by studying the antioxidant effects of PFAs one derived from an olive oil byproduct and another based on a spice blend. Three experimental trials were conducted. Experiments 1 and 2, sharing the same design, compared these PFAs alone or combined with diets containing conventional vitamin E levels (experiment 1) or no synthetic vitamin E (experiment 2). Experiment 3 assessed their antioxidant capacity in feeds containing fresh or peroxidized soybean oil. In diets with 20 ppm of vit E, increasing the level to 100 ppm or the inclusion of PFAs did not affect productive performance or plasma antioxidant enzyme activity (experiment 1). However, when diets had no vit E added, productivity decreased during the first weeks compared to birds receiving 100 ppm (experiment 2). Phytogenic additives maintained the productivity, suggesting a positive effect on the control of oxidative stress at the critical starting period. In the second period, no significant differences were observed, highlighting that chickens can partially control oxidative stress even with low vit E levels. Comparing the mechanisms of actions of the vit E to those of the PFAs, a higher activity of glutathione peroxidase was observed in the plasma of the birds fed 100 ppm of vit E and the PFAs. Besides, the effects of the olive extracts seem to be mediated by the modulation of the heat shock protein 70 (HSP70). In experiment 3, the birds fed peroxidized fats did not show a significative loss of productivity. However, an enzymatic and non-enzymatic response was observed with broilers fed the peroxidized oil showing higher plasma FRAP, DPPH and catalase (CAT) activity. This response was more attenuated and controlled in those birds supplemented with the olive extract. In none of the experiments, synergies between the PFAs, nor the PFAs and the vit E were reported. In conclusion, although with limited effects on productive performance, the PFAs tested in the present thesis seem to help to the control of oxidative stress. In the case of the spice extract, the results are consistent with the concept of hormesis, involving low level activation of antioxidant enzymes such as GPx and CAT without an accompanying increase in HSP70, which is indicative of low stress conditions. In contrast, the olive extract appears to maintain very low HSP70 levels under standard conditions while simultaneously increasing or decreasing GPx and maintaining or decreasing CAT activity and gene expression. This response suggests a more effective control of the oxidative environment, potentially through direct regulation of HSP70 or by maintaining low levels of reactive oxygen species via direct radical scavenging. RESUMEN Durante su ciclo productivo, los pollos broiler están expuestos a múltiples estresores que aumentan la producción de especies reactivas de oxígeno, provocando un desequilibrio entre sistemas prooxidantes y antioxidantes endógenos. Este desequilibrio causa estrés oxidativo, que afecta negativamente la salud, el crecimiento y la función inmunitaria, incrementando la susceptibilidad a procesos infecciosos y patológicos. Para contrarrestar la peroxidación lipídica y otros daños oxidativos, se añaden antioxidantes sintéticos a la dieta, siendo la vitamina E (-tocoferol) el compuesto de referencia por su capacidad de estabilizar radicales y proteger membranas biológicas. Sin embargo, el alto coste y la variabilidad de precio de la vitamina E sintética, junto con la necesidad de una producción avícola más sostenible, han impulsado la búsqueda de antioxidantes alternativos. Los aditivos fitogénicos (PFAs), ricos en compuestos bioactivos, pueden mejorar el estado antioxidante, apoyar la inmunidad, actuar como biocidas o mejorar la digestibilidad. Muchos PFAs proceden de subproductos agroalimentarios, contribuyendo a estrategias de economía circular. Su uso ha aumentado en los últimos años, aunque se requiere más investigación para aclarar sus mecanismos de acción y posibles sinergias con aditivos como la vitamina E. Esta tesis estudia los efectos antioxidantes de dos PFAs: uno derivado de un subproducto del aceite de oliva y otro basado en una mezcla de especias. Se realizaron tres ensayos. Los experimentos 1 y 2, con el mismo diseño, compararon estos PFAs solos o combinados con dietas con niveles convencionales de vitamina E (experimento 1) o sin vitamina E sintética (experimento 2). El experimento 3 evaluó su capacidad antioxidante en piensos con aceite de soja fresco o peroxidado. En dietas con 20 ppm de vitamina E, subir a...