Genetic parameters and mapping quantitative trait loci associated with tibia traits in broilers.

Abstract: Selection among broilers for performance traits is resulting in locomotion problems and bone disorders, once skeletal structure is not strong enough to support body weight in broilers with high growth rates. In this study, genetic parameters were estimated for body weight at 42 days of age (BW42), and tibia traits (length, width, and weight) in a population of broiler chickens. Quantitative trait loci (QTL) were identified for tibia traits to expand our knowledge of the genetic architecture of the broiler population. Genetic correlations ranged from 0.56 +/- 0.18 (between tibia length and BW42) to 0.89 +/- 0.06 (between tibia width and weight), suggesting that these traits are either controlled by pleiotropic genes or by genes that are in linkage disequilibrium. For QTL mapping, the genome was scanned with 127 microsatellites, representing a coverage of 2630 cM. Eight QTL were mapped on Gallus gallus chromosomes (GGA): GGA1, GGA4, GGA6, GGA13, and GGA24. The QTL regions for tibia length and weight were mapped on GGA1, between LEI0079 and MCW145 markers. The gene DACH1 is located in this region; this gene acts to form the apical ectodermal ridge, responsible for limb development. Body weight at 42 days of age was included in the model as a covariate for selection effect of bone traits. Two QTL were found for tibia weight on GGA2 and GGA4, and one for tibia width on GGA3. Information originating from these QTL will assist in the search for candidate genes for these bone traits in future studies.

Phytate-phosphorus and phytase contents on the relative weight of organs, intestinal morphometry and performance of broilers.

ABSTRACT: In order to evaluate the efficiency of phytase in diets with low and high phytate phosphorus (PP) content, as a consequence of wheat bran inclusion, on the relative weight of organs, intestinal morphometry and performance, three hundred and eighty-four male Cobb500 broilers were housed in metabolic cages. Animals were assigned into four treatments in a 2x2 factorial scheme in a randomized block design with eight replicates of 12 birds each. From 11 days of age birds received experimental diets, which consisted of: Diet low in PP; Diet low in PP with phytase (500FTU kg-1); Diet with a high PP and Diet with a high PP with phytase (500FTU kg-1). At 22 and 32 days of age two birds were slaughtered in order to collect gizzard, heart, liver, cecum, cloacal bursa, and at 32 days, a portion of the duodenum, jejunum and ileum was collected for morphometric evaluation. From 22 to 32 days of age average feed intake, average weight gain, average body weight and feed conversion ratio were also evaluated. Data were subjected to analysis of variance, fixed effects of diet and phytase and interaction between factors as well as the random block effects were tested. There was no significant interaction for the variables studied, concluding that phytase in diets with low or high phytate phosphorus content did not change the relative weight of organs, intestinal morphometrics and performance; only isolated effects were observed. RESUMO: Para avaliar a eficiência da fitase em dietas com baixo e alto teor de fósforo fítico (PP), em função da inclusão ou não do farelo de trigo, sobre o peso relativo de órgãos, morfometria intestinal e desempenho, foram alojados 384 frangos de corte, machos da linhagem Cobb500, em gaiolas metabólicas. Os animais foram distribuídos em quatro tratamentos em um arranjo fatorial 2x2 em delineamento de blocos casualizados com oito repetições e 12 aves por unidade experimental (UE). A partir de 11 dias de idade as aves receberam as dietas experimentais, que consistiram em: Dieta com baixo teor de PP; Dieta com baixo teor de PP com fitase (500FTU kg-1); Dieta com alto teor de PP e Dieta com alto teor de PP com fitase (500FTU kg-1). Aos 22 e 32 dias de idade foram abatidas duas aves por UE para coletar a moela, coração, fígado, ceco, bolsa cloacal, e aos 32 dias foi coletada uma porção do duodeno, jejuno e íleo para avaliação da morfometria. No período de 22 a 32 dias de idade foram avaliados o consumo médio de ração, ganho de peso médio, peso médio corporal e a conversão alimentar. Os dados foram submetidos à análise de variância, onde foram testados os efeitos fixos de dieta e fitase e a interação entre os fatores, bem como o efeito aleatório de bloco. Não foi observada interação significativa para nenhuma das variáveis estudadas, concluindo-se que a fitase em dietas com baixo ou alto de PP não altera o peso relativo dos órgãos, a morfometria intestinal e o desempenho, apenas efeitos isolados foram observados.