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Introduction
The comb is an ornamental organ in chicken which can be used as an indicator of health and sexual maturity. Red jungle fowl are the ancestors of domestic chickens, and are highly sexually dimorphic, with the male possessing a red fleshy comb and wattles as well as bright plumage, while the female is relatively drab (Zuk et al., 1990a; 1990b). The scientific name for the chickens, Gallus domesticus (Bálint et al., 2011), reflects the importance of the comb, as Gallus means comb (Anderson, 2011). The variety of chicken combs in the world today can be traced back to only two types of genes; pea comb and rose comb genes. The American Poultry Association recognises nine different kinds of combs; pea, rose, single, carnation or king's, buttercup, cushion, strawberry, silkie and walnut (Anderson, 2011).
Comb colour and size in birds is an indicator of cell mediated immunity (Mougeot et al., 2004; Mougeot, 2008) and a healthy comb is generally an indicator of health status, disease resistance and nutritional status in the flock (Zuk et al., 1990a; 1990b; Johnson et al., 1993). Chicken comb is used for sexual selection in all types of conditions (Rydmel, 2010), and is an important secondary sexual characteristic which indicates the bird's hormone status. A lengthy comb indicates a male and a less developed comb indicates a female in chickens. Comb type is the result of gene interaction but comb size is associated with gonadal development (North and Bell, 1990). Hamilton and Zuk (1982) proposed the immuno-competence handicap theory and reported that well developed secondary sexual characters are an indicator of freedom from or resistance to parasites or diseases. As a result, a longer redder comb in red jungle fowl cockerels is chosen preferentially by hens (Zuk et al., 1995; Johnsen and Zuk, 1996). The aim of this review is to describe the relationship of productive and reproductive responses with the comb size of dam and sire in the flock and also use this indicator (comb) for the selection of different traits in poultry breeding.
Morphology and development of the comb
The comb of birds is generally vacillated during different behaviours (Rintamaki et al., 2000). In male Gallus...