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Effectiveness of betaine, taurine, and myo-inositol in normalizing the antioxidant status of laying hens under heat stress

D. B. Perederiy

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Institute of Animal Biology NAAS, 38 V. Stusa str., Lviv, 79034, Ukraine

Heat stress is a critical factor in the adaptation of animals to changing environmental temperature conditions and can significantly impact their health. Elevated ambient temperatures induce considerable stress, potentially leading to various adverse effects in poultry, including impairments in the antioxidant system. The imbalance between antioxidant and pro-oxidant processes can result in the excessive formation of free radicals, which harm cells and may contribute to the development of diseases. This study investigates the effects of artificially induced heat stress on the antioxidant system and lipid peroxidation products in the blood of laying hens. Laying hens, as commercial poultry lines selected for high egg productivity, are particularly vulnerable to high ambient temperatures due to their intensive metabolism, increased energy demand for egg production, and limited thermoregulatory capacity compared to other bird species. In intensive poultry farming, where bird density is high, these factors can exacerbate heat stress. The study aimed to identify changes in specific indicators of the antioxidant system and the content of lipid peroxidation products in the blood of chickens under the influence of betaine, taurine and myo-inositol. Analyzing parameters such as lipid hydroperoxides (LOOH), reduced glutathione (GSH), glutathione peroxidase (GSH-Px), glutathione reductase (GR), catalase (CAT), and superoxide dismutase (SOD) provides insights into the antioxidant defense system and oxidative stress levels under heat stress conditions. The study involved 15 laying hens housed in the vivarium of the Institute of Animal Biology NAAS, and was conducted in two phases. During the first phase, hens were kept at an ambient temperature of 20°C for three weeks. During the second phase, heat stress conditions were simulated by raising the temperature to 30°C for 6 hours daily over 7 days. Birds were divided into two groups: the control group (fed a standard diet) and the experimental group (supplemented with 0.5 g/kg betaine, 5 g/kg taurine, and 2 g/kg myo-inositol). Results showed that with increased ambient temperature in the control group, the content of LOOH decreased by 63% (P<0.05), while the activities of CAT, SOD, GSH-Px, and GR decreased by 28% (P<0.001), 49% (P<0.01), 15% (P<0.01), and 30% (P<0.01), respectively, compared to thermoneutral conditions. Conversely, GSH content increased by 37% (P<0.01). In the experimental group supplemented with betaine, taurine, and myo-inositol, CAT, GSH-Px, and GR activities decreased by 14% (P<0.01), 30% (P<0.001), and 23% (P<0.05), respectively, under thermoneutral conditions. Under heat stress conditions, LOOH content decreased by 59% (P<0.05), and GSH-Px activity decreased by 15% (P<0.01), while SOD and CAT activities increased by 55% (P<0.001) and 11% (P<0.05), respectively, compared to the control. The findings indicate the positive effects of betaine, taurine, and myo-inositol on the antioxidant system of laying hens under heat stress. The results highlight the potential of these supplements as effective strategies to maintain poultry health and productivity during heat stress.

Key words: laying hens, heat stress, oxidative stress, antioxidant defense system