1- Agricultural Sciences and Natural Resources University of Khuzestan
Abstract: (23 Views)
Introduction and Objective: Thyroid hormones play a crucial role in regulating metabolism and physiological processes in broiler chickens. These hormones, primarily thyroxine (T4) and triiodothyronine (T3), directly affect the growth rate of the chickens because they regulate the enzymatic activities involved in converting food components into energy and muscle proteins, thus helping the body grow faster. Increased levels of thyroid hormones can stimulate growth by enhancing muscle tissue development, thereby improving overall production performance. This accelerated growth and muscle development is a major goal in broiler production, as it leads to higher meat yield within a shorter period. On the other hand, a deficiency in these hormones leads to a decrease in metabolic rate, resulting in slower growth and potential weight gain deficits. Chickens may fail to gain adequate weight, negatively affecting meat production. Thyroid hormones also assist in improving digestion and nutrient absorption from food. In hypothyroidism, the efficiency of converting food into energy decreases, which can lead to stunted growth and reduced production performance. Given these essential roles, the aim of this study was to examine the effects of induced hypothyroidism and hyperthyroidism on the growth performance of broiler chickens, to better understand the impact of changes in thyroid hormone levels on growth rate, food consumption, and food conversion efficiency to body weight. Given the crucial role of thyroid hormones in poultry metabolism, understanding how to manipulate these hormone levels could have significant practical applications in the poultry industry. This research could also inform future studies on hormone regulation and feed management, paving the way for more sustainable and efficient poultry production practices.
Materials and Methods: In this study, broiler chickens were subjected to various treatments to induce hypothyroid and hyperthyroid conditions. The hypothyroid group was treated with the thyroid inhibitor, propylthiouracil (PTU), while the hyperthyroid group received the thyroid-stimulating hormone, levothyroxine. The effects of these treatments on various growth parameters, including body weight, feed intake, and feed conversion efficiency, were investigated. A total of 216 one-day-old Ross 308 broiler chicks were used for a 35-day trial. Three experimental groups (6 replications, 12 chicks per replication) were set up in a completely randomized design as follows: 1) control group (Tc) with a basal diet without any drug supplementation, 2) basal diet + 50 µg levothyroxine per kg of diet to induce hyperthyroidism (from day 7 to 35; TL), and 3) basal diet + 5 mg PTU per kg of diet to induce hypothyroidism (from day 7 to 21) + 50 µg levothyroxine to compensate for hypothyroidism (from day 21 to 35; TPL). Experimental diets were formulated using UFFDA software, based on the nutritional requirements of Ross broiler chickens (2021). Metabolizable energy (ME) and crude protein (CP) levels were kept constant across all treatment levels in each phase. Performance parameters, including feed intake, feed conversion ratio (FCR), and body weight gain, were evaluated and recorded weekly from day 7 to the end of the experiment (35 days). To determine the average weight gain for each experimental group, all birds in each group were weighed at the end of every week. The average weight gain (in grams per period) was then calculated using the chick-day method. The FCR was calculated by dividing the average feed intake by the average body weight gain for each experimental unit during each period.
Results: During the first week of recording, which included days 7 to 14, no significant differences were observed in any of the parameters (P > 0.05). In days 14 to 21 of the trial, the TPL treatment group showed the highest feed intake and feed conversion ratio compared to the other groups (P < 0.05). This increased feed intake and high feed conversion ratio may be due to reduced metabolic efficiency caused by hypothyroidism. In fact, with decreased thyroid hormone levels, the metabolism of the chicks slowed down, and the body required more feed to compensate for this metabolic reduction. In the fourth week, after discontinuing PTU as the thyroid inhibitor and adding levothyroxine as a thyroid stimulant, the highest feed intake and feed conversion ratio were still observed in the TPL group (P < 0.05). This indicates that even with hormonal changes and the inclusion of levothyroxine, the negative effects on feed performance and its conversion to body weight were not completely eliminated, and the TPL group still showed high feed intake and feed conversion ratio. This may be due to the time required for metabolic recovery following the treatment. In other words, the effects of hypothyroidism may persist for a while even after the introduction of levothyroxine. In the fifth week (days 28-35), although feed intake in the TPL group was significantly higher than in the other groups, there were no significant changes in the feed conversion ratio.
Conclusion: The present study concludes that hormonal changes at the thyroid level affect the growth and feed efficiency in broiler chickens. Although hyperthyroidism does not significantly affect the growth performance of Ross broiler chickens under normal conditions, hypothyroidism in normal breeding environments can significantly increase feed consumption and feed conversion ratio, thereby reducing their economic efficiency.
Materials and Methods: In this study, broiler chickens were subjected to various treatments to induce hypothyroid and hyperthyroid conditions. The hypothyroid group was treated with the thyroid inhibitor, propylthiouracil (PTU), while the hyperthyroid group received the thyroid-stimulating hormone, levothyroxine. The effects of these treatments on various growth parameters, including body weight, feed intake, and feed conversion efficiency, were investigated. A total of 216 one-day-old Ross 308 broiler chicks were used for a 35-day trial. Three experimental groups (6 replications, 12 chicks per replication) were set up in a completely randomized design as follows: 1) control group (Tc) with a basal diet without any drug supplementation, 2) basal diet + 50 µg levothyroxine per kg of diet to induce hyperthyroidism (from day 7 to 35; TL), and 3) basal diet + 5 mg PTU per kg of diet to induce hypothyroidism (from day 7 to 21) + 50 µg levothyroxine to compensate for hypothyroidism (from day 21 to 35; TPL). Experimental diets were formulated using UFFDA software, based on the nutritional requirements of Ross broiler chickens (2021). Metabolizable energy (ME) and crude protein (CP) levels were kept constant across all treatment levels in each phase. Performance parameters, including feed intake, feed conversion ratio (FCR), and body weight gain, were evaluated and recorded weekly from day 7 to the end of the experiment (35 days). To determine the average weight gain for each experimental group, all birds in each group were weighed at the end of every week. The average weight gain (in grams per period) was then calculated using the chick-day method. The FCR was calculated by dividing the average feed intake by the average body weight gain for each experimental unit during each period.
Results: During the first week of recording, which included days 7 to 14, no significant differences were observed in any of the parameters (P > 0.05). In days 14 to 21 of the trial, the TPL treatment group showed the highest feed intake and feed conversion ratio compared to the other groups (P < 0.05). This increased feed intake and high feed conversion ratio may be due to reduced metabolic efficiency caused by hypothyroidism. In fact, with decreased thyroid hormone levels, the metabolism of the chicks slowed down, and the body required more feed to compensate for this metabolic reduction. In the fourth week, after discontinuing PTU as the thyroid inhibitor and adding levothyroxine as a thyroid stimulant, the highest feed intake and feed conversion ratio were still observed in the TPL group (P < 0.05). This indicates that even with hormonal changes and the inclusion of levothyroxine, the negative effects on feed performance and its conversion to body weight were not completely eliminated, and the TPL group still showed high feed intake and feed conversion ratio. This may be due to the time required for metabolic recovery following the treatment. In other words, the effects of hypothyroidism may persist for a while even after the introduction of levothyroxine. In the fifth week (days 28-35), although feed intake in the TPL group was significantly higher than in the other groups, there were no significant changes in the feed conversion ratio.
Conclusion: The present study concludes that hormonal changes at the thyroid level affect the growth and feed efficiency in broiler chickens. Although hyperthyroidism does not significantly affect the growth performance of Ross broiler chickens under normal conditions, hypothyroidism in normal breeding environments can significantly increase feed consumption and feed conversion ratio, thereby reducing their economic efficiency.
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