Native chicken breeding station of Mazandaran was established in 1988 with two main objectives: genetic improvement through selection programs and dissemination of indigenous Mazandarani birds. (Co)variance components and genetic parameters for economically important traits were estimated using (bi) univariate animal models with ASREML procedure in Mazandarani native chicken. The data were from 18 generations of selection (1988-2009). Heritability estimates for body weight at different ages [at hatch (bw1), 8 (bw8), 12 (bw12) weeks of ages and sex maturation (wsm)] ranged from 0.24 ± 0.00 to 0.47 ± 0.01. Heritability for reproductive traits including age at sex maturation (asm); egg number (en); weight of first egg (ew1); average egg weight at 28 (ew28), 30 (ew30), and 32 (ew32) weeks of age; their averages (av); average egg weight for the first 12 weeks of production (ew12); egg mass (em); and egg intensity (eint) varied from 0.16 ± 0.01 to 0.43 ± 0.01. Generally, the magnitudes of heritability for the investigated traits were moderate. However, egg production traits showed smaller heritability compared with growth traits. Genetic correlations among egg weight at different ages were mostly higher than 0.8. On the one hand, body weight at different ages showed positive and relatively moderate genetic correlations with egg weight traits (ew1, ew28, ew30, ew32, ew12, and av) and varied from 0.30 ± 0.03 to 0.59 ± 0.02. On the other hand, low negative genetic correlations were obtained between body weight traits (bw1, bw8, bw12, and wsm) and egg number (en). Also, there is low negative genetic correlation (-24 ± 0.04 to -29 ± 0.05) between egg number and egg weight. Therefore, during simultaneous selection process for both growth and egg production traits, probable reduction in egg production due to low reduction in egg number may be compensated by increases in egg weight.

The anatomical structure and function of beaks, bills and tongue together with the mechanics of deglutition in birds have contributed to the development of a taste system denuded of macrostructures visible to the human naked eye. Studies in chickens and other birds have revealed that the avian taste system consists of taste buds not clustered in papillae and located mainly (60 %) in the upper palate hidden in the crevasses of the salivary ducts. That explains the long delay in the understanding of the avian taste system. However, recent studies reported 767 taste buds in the oral cavity of the chicken. Chickens appear to have an acute sense of taste allowing for the discrimination of dietary amino acids, fatty acids, sugars, quinine, Ca and salt among others. However, chickens and other birds have small repertoires of bitter taste receptors (T2R) and are missing the T1R2 (related to sweet taste in mammals). Thus, T1R2-independent mechanisms of glucose sensing might be particularly relevant in chickens. The chicken umami receptor (T1R1/T1R3) responds to amino acids such as alanine and serine (known to stimulate the umami receptor in rodents and fish). Recently, the avian nutrient chemosensory system has been found in the gastrointestinal tract and hypothalamus related to the enteroendocrine system which mediates the gut-brain dialogue relevant to the control of feed intake. Overall, the understanding of the avian taste system provides novel and robust tools to improve avian nutrition.

To study the efficiency of Bacillus spp. probiotics administered via different routes and doses, a 6-week grow-out trial was conducted using a total of 378 day-old mixed-sex ROSS308 broiler chickens in a completely randomized block design. Six experimental diets included probiotics added at two different inclusion rates into the feed (250 g/ton; PRO250, or 500 g/ton; PRO500), or in the drinking water (25 g/L; PRO-WS), or as a feed synbiotic (250 g probiotic + 250 g/ton prebiotic; SYN), compared to a negative (NC; without additives) and positive control (PC; with antibiotics) diets. The PRO-WS enhanced feed intake (p < 0.05) and tended to improve average daily gain and final body weight (p = 0.14). Broiler gut morphology in the duodenum including the villus height (p = 0.04), villus width (p = 0.05) and crypt depth (p = 0.02) were improved by PRO500. Firmicutes was the most abundant phylum, followed by Bacteroidetes. Streptococcaceae, Lachnoospiraceae, Peptostreptococcaceae, Ruminococcaceae, and Erysipe-lotrichaceae were the top five most abundant families. Antibiotic inclusion in PC reduced microbial beta-diversity and increased similarity compared to probiotic inclusion (p = 0.05). Probiotic inclusion reduced the relative abundance of Bacteroides fragilis, which is a commonly isolated pathogen and is considered as a marker for antimicrobial resistance. Overall, probiotic supplementation via feed or water may potentially improve the production performance of the broiler chickens, and water-soluble probiotics are potentially more effective. Probiotics, especially when added to water, suggest a promising feed additive to support gut microbial maturation and diversity, and may reduce resistant bacteria in broiler chickens. However, it is suggested that the best route for the administration of probiotics be further examined under commercial conditions to find the most effective and practical application method that yields the most consistent results.