Catia Chilanti Pinheiro

Effects of the reduction of dietary heat increment on the performance, carcass yield, and diet digestibility of broilers submitted to heat stress

This experiment aimed at verifying the effect of different diets and thermal environments on the performance, carcass yield, and diet digestibility of 21 to 42-day-old broilers. A total number of 288 21-dayold male Ross broilers were distributed in a 2 x 2 + 2 factorial arrangement, with six replicates, including the following factors: two environments (TNE – thermoneutral: 21-25°C and 73% RH; CHS – cyclic heat stress: 25-32°C and 65%RH), and two diets (control: 2.4% soybean oil and 19.5% protein; summer: 4.0% soybean oil and 18.5% protein). In TNE, two additional treatments were included with feed restriction of birds fed both the control and summer diets (pair-feeding), thereby maintaining the same feed intake level for both types of diet. Diet did not influence performance, dry matter and protein digestibilities, or carcass and part yields. TNE birds had better performance (p<0.001) as compared to CHS birds, but FCR was not different. CHS birds had lower breast yield (p<0.0001), and higher thigh yield (p<0.02) than TNE birds. In the pair-feeding treatments, environment did not influence performance, but dry matter digestibility was significantly lower in CHS (p<0.03), whereas protein digestibility was not affected. The difference in feed intake was the main responsible factor for the variation in the performance of heat-stressed birds.

Effect of the supplementation of vitamins and organic minerals on the performance of broilers under heat stress

The objective of this experiment was to evaluate the effect of diet supplementation with vitamins C and E and organic minerals Zn and Se on the performance of 1 to 35 day-old broilers from, kept under cyclic heat stress (25 to 32°C). Four levels of vitamin-mineral supplementation were used (T1-control diet (60/30 IU of vit E for starter and growing diet, respectively, zero vit. C, 80 ppm of inorganic Zn, 0.3 ppm of inorganic Se); T2-control diet + 100 UI vit E and 300 ppm vit C/kg; T3control diet + 40 ppm Zn and 0,3 ppm Se/kg; T4-control diet + T2 and T3 levels) and two environments - thermoneutral and cyclic heat stress (TN and HS) from 14 to 35 days of age. In the period when part of the birds was submitted to HS, from 14 to 35 days, it was observed lower feed intake (FI) and better feed conversion (FC) for HS birds receiving supplementation compared to the group without supplementation. Evaluating the total period, all the types of supplementation provided lower FI and better FC than the control treatment, but not affected weight gain (WG). The supplementation of vitamins C and E and/or organic minerals Zn and Se improved the performance of birds due to a lower FI resulting in better FC, independently on the environment.

Effect of vitamin E levels on the cell-mediated immunity of broilers vaccinated against coccidiosis

Studies on the relationships between animal nutrition and immunity have sought reliable methodologies to measure responses. Cellmediated immune response is similarly studied in humans. The cutaneous basophil hypersensitivity test (CBH) is one of the methods to measure that response and consists in the infiltration of inflammatory cells, particularly of lymphocytes and basophils, as result of the application of substances capable of inducing cell proliferation in determined sites, such as wings, wattle, and interdigital space in birds. CBH is considered a simple and fast method and can be applied in birds of different ages. In immunocompetence studies with poultry, phytohemagglutinin-P (PHA-P) is a commonly used substance, despite the variability of the response related to the method of application (intradermal injection) and the antigens used. In the present experiment, PHA-P was used to observe the cell-mediated immune response of 216 chicks fed three dietary levels of vitamin E from 1 to 36 days of age. All birds were immunologically challenged by vaccination against coccidiosis at three days of age and against Newcastle Disease (NCD) at 14 and 30 days of age. At 36 days of age, birds were submitted to the CBH test according to the methodology of Corrier & DeLoach (1990). Birds fed 65mg/kg of vitamin E presented lasting cell reaction (p £0.08), which indicates that this vitamin E level improved cell immune response of birds due to its antioxidant and immunomodulating properties. The use of this vitamin E level can be considered by nutritionists under practical conditions, aiming to improve broiler immunity.