Chromium-methionine and zinc-l-selenomethionine in diets of broiler chickens subjected or not to cyclic heat stress

Abstract

In this study, four experiments were conducted to evaluate the effects of graded inclusions of chromium-methionine (CrMet) or zinc-l-selenomethionine (Zn-L-SeMet) in diets of broiler chickens from 1 to 42 days of age subjected or not to cyclic heat stress (CHS) conditions and its effects on growth performance, cloacal temperatures, mortality, carcass and parts yield, liver and fat pad relative weights, plasma metabolites, enzymes, and hormones. Additionally, the study assessed the scores of incidence and severity of wooden breast (WB) and white striping (WS) myopathies in the breast muscle as well as breast meat quality, lipid peroxidation, chemical composition, and insulin-like growth factor and growth hormone receptor gene expression. For this purpose, two experiments were carried out (one for each mineral) where the animals were reared under thermoneutral (TN) conditions from 1 to 42 days of age, and another two experiments (one for each mineral) from 1 to 42 days of age, subjecting the animals to CHS conditions from 22 to 42 days of age. For each experiment, a total of 1,000 one-day-old male Cobb 500® broiler chicks were distributed in a completely randomized design composed by 5 dietary treatments and 10 replicate pens (experimental units) with 20 animals per pen. The animals received food and water ad libitum throughout the experimental period. The experimental diets involving CrMet were formulated with similar inclusion levels for both TN and CHS experiments as follows: 0 (basal diet without CrMet inclusion); 0.25 (basal diet + 0.25 mg/CrMet/kg of feed); 0.50 (basal diet + 0.50 mg/CrMet/kg of feed); 1.0 (basal diet + 1.0 mg/CrMet/kg of feed); and 2.0 (basal diet + 2.0 mg/CrMet/kg of feed). Similarly, the experimental treatments regarding Zn-L-SeMet were formulated with similar inclusion levels for both TN and CHS conditions as follows: 0 (basal diet without Zn-L-SeMet inclusion); 0.13 (basal diet + 0.13 mg/Zn-L-SeMet/kg of feed); 0.23 (basal diet + 0.23 mg/Zn-L-SeMet/kg of feed); 0.47 (basal diet + 0.47 mg/ Zn-L-SeMet/kg of feed); and 1.30 (basal diet + 1.30 mg/Zn-L-SeMet/kg of feed). Based on the results of the experiments, for broilers reared under TN conditions the inclusion of 2.0 mg/CrMet/kg is recommended to improve FI and BWG from 1 to 42 days of age and reduce breast meat lightness, while inclusions of 1.04 and 1.0 mg/CrMet/kg reduced redness and total ash in the breast muscle, respectively. Considering the experiment evaluating Zn-L-SeMet, inclusions of 0.64, 0.78, and 1.05 mg/Zn-L-SeMet/kg are recommended to improve FI, BWG, and FCR from 1 to 42 days of age, respectively. In addition, the inclusion of 0.61 mg/Zn-L-SeMet/kg reduces blood creatinine, while TA content in the breast linearly decreases as Zn-L-SeMet levels increase. For broilers reared under CHS, the inclusion of 0.75 and 0.88 mg/CrMet/kg are recommended to improve FCR from 1 to 21 and 1 to 42 days of age, respectively. The inclusions of 0.25 and 2.0 mg/CrMet/kg are recommended to reduce mortality rate and blood triglycerides, respectively. Finally, the inclusion of 0.71 mg/Zn-LSeMet/kg is recommended to improve growth performance from 1 to 42 days of age and reduce the mortality rate.