Abstract
A two level factorial experiment (3 × 3) was designed to evaluate the effect of dietary inclusion level of probiotic and breed on productive performance, immune status and egg quality characteristics in laying hens reared under high ambient temperature. A total of 216, 32-week-old laying hens representing three different breeds (White Leghorn, Saudi black and Saudi brown) were randomly assigned to three dietary treatments (0, 200 and 400 g/t feed) in a 90-d experiment. The current results indicated that the inclusion of probiotics in layer diets did not appear to cause any adverse effects on egg production traits compared with non-treated hens. Dietary supplementation with probiotics at 400 ppm level significantly (p < .05) increased shell thickness compared to non-treated laying hens. Moreover, an improvement in eggshell quality and breaking strength in hens fed a diet containing probiotics was observed under high ambient temperature. Also, plasma cholesterol and triglyceride were reduced in laying hens fed a diet supplemented with probiotics. Furthermore, probiotic inclusion significantly increased IgM immunoglobulin concentration in laying hens fed a diet containing either 200 or 400 ppm compared with untreated hens. Concerning breed effect, Saudi black laying hens recorded significantly (p < .02) higher egg mass compared with the other breeds. Also, both Saudi chicken breeds exhibited significantly higher cell-mediated response and IgM concentration compared with Leghorn hens.